|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
Lecture notes, cheat sheets
Materials Science. Cheat sheet: briefly, the most important
Directory / Lecture notes, cheat sheets Table of contents
1. The subject of materials science; modern classification of materials, main stages in the development of materials science Materials science studies the composition, structure, properties and behavior of materials depending on environmental influences. The impact can be thermal, electrical, magnetic, etc. Any component of structures or structures is subjected to loads both from other components and from the external environment. Classification of materials: metallic, non-metallic and composite materials. Metal materials are divided into non-ferrous metals, powder materials. Non-metallic materials: rubber, glass, ceramics, plastics, glass-ceramics. Composite materials are composite materials, which include two or more materials (fiberglass). There is a classification of materials depending on the type of semi-finished products: sheets, powders, granules, fibers, profiles, etc. The technique of creating materials is the basis for the classification by structure. Metallic materials are divided into groups according to the component that underlies them. Ferrous metallurgy materials: steel, cast irons, ferroalloys, alloys in which the main component is iron. Non-ferrous metallurgy materials: aluminum, copper, zinc, lead, nickel, tin. The basis of modern technology is made up of metals and metal alloys. Today, metals are the most versatile class of materials in terms of application. In order to improve the quality and reliability of products, new materials are required. Composite, polymeric, powder materials are used to solve these problems. Metals are substances that have malleability, luster, electrical conductivity and thermal conductivity. In engineering, all metallic materials are called metals and are divided into two groups. Base metals - metals that have a small amount of impurities of other metals. Compound metals - metals that are combinations of a simple metal as a base with other elements. Three quarters of all elements in the periodic table are metals. Materials science or the science of materials has been developed since ancient times. The first stage in the development of materials science begins with the specialized manufacture of ceramics. A special contribution to the development of materials science in Russia was made by M.V. Lomonosov (1711-1765) and D.I. Mendeleev (1834-1907). Lomonosov developed a course in physical chemistry and chemical atomistics, confirmed the theory of the atomic and molecular structure of matter. Mendeleev is credited with the development of the periodic table of elements. Both scientists paid considerable attention to the problem of glass production. In the XNUMXth century contribution to the development of materials science was made by F.Yu. Levinson-Lessing, E.S. Fedorov, V.A. Obruchev, A.I. Fersman, N.N. Belelubsky. New materials are being produced: Portland cement, new gypsums, cement concretes, polymeric materials, etc. In mechanical engineering, metals and metal alloys are widely used, which is why metal science is an important part of materials science. Metal science as a science arose in Russia in the XNUMXth century; it is the scientific basis for the development of new optimal technological processes: heat treatment, casting, rolling, stamping, welding. The combination of high strength and hardness with good ductility, toughness and machinability, not found in other materials, was the reason for the use of metals as the main structural material in all areas of technology. For the first time, the existence of a connection between the structure of steel and its properties was established by the outstanding Russian scientist P.P. Anosov (1799-1851), who revealed the long-lost secret of making and obtaining by the ancient masters of the East damask steel, which is used for the production of blades. Anosov's damask steel was famous all over the world and was even exported abroad. The blades that were made from this steel were distinguished by high hardness and toughness. P.P. Anosov is considered the "initiator" of the production of high-quality steel, he was the first to use a microscope to determine the structure of steel and initiated the study of the regular relationship between the structure and properties of alloys. The founder of scientific metallurgy D.K. Chernov (1839-1921), who discovered phase transformations in steel in 1868. Discovery of D.K. Chernov critical points a and b (according to the modern designation A1 and A3) revolutionized the knowledge of the nature of metal alloys and made it possible to explain a number of "mysterious" phenomena that occur during the heat treatment of steels. A huge contribution to the development of the science of metals was made by N.S. Kurnakov, A.A. Baikov, N.T. Gudtsov, A.A. Bochnar, G.V. Kurdyumov, S.S. Shteyiberg, A.P. Gulyaev, as well as other Soviet scientists. Of great importance in the development of metal science and heat treatment were the works of Osmond (France), Seitz, Bain and Meil (USA), Tammann and Hahnemann (Germany). In the XNUMXth century, major achievements were made in the theory and practice of materials science, high-strength materials for tools were created, composite materials were developed, the properties of semiconductors were discovered and used, methods for strengthening parts by thermal and chemical-thermal treatment were improved. 2. Grain structure of metals. Grain and subgrain boundaries Metals are polycrystalline bodies, they consist of small crystals. They are characterized by metallic properties and make up 50% of all chemical elements. The structure of metals and their alloys is crystalline. In the process of crystallization, the crystals acquire an irregular shape. They are called grains. Each grain has its own crystal lattice orientation, which differs from the orientation of neighboring grains. The grain size of a metal affects its mechanical properties. These properties, toughness and plasticity, are much higher if the metal has a fine grain. Grain interfaces are called grain boundaries, which can be: inclined when the axis of rotation is located in the same plane as the boundary; twisted with the axis perpendicular to the plane. Such a piece of metal is a polycrystal. The grain boundaries are determined by the points of contact between adjacent crystals. The size, structure and nature of the structure of the grains can be judged from the fractures of the metal. In polycrystalline materials, the grain size is from 1 to 1000 microns. The grains are disoriented, rotated one relative to the other up to tens of degrees. Boundaries are the main defect in metals. At the boundaries between the grains, the atoms do not have the correct arrangement. There is a transition region several atomic diameters wide, in which the lattice of one grain passes into the lattice of another grain with a different orientation. The structure of the transition layer (boundary) contributes to the accumulation of dislocations in it, since when passing through the boundary, neither the slip plane nor the Burgers vector remain unchanged. Violation of the correct arrangement contributes to the fact that at the grain boundaries the concentration of those impurities that lower the surface energy is increased. Inside the grains, the correct crystalline structure is disturbed. The boundaries of subgrains are less disturbed. All metals have common properties: ductility, high thermal and electrical conductivity, specific metallic luster, increase electrical resistance with increasing temperature. A single crystal grows from a liquid melt, which is a single crystal. The sizes of single crystals are small, they are used in laboratories to study the properties of any substance. Metals and alloys, which are obtained under the most ordinary conditions, consist of a large number of crystals, they have a polycrystalline structure. The study of the structure of metals using X-ray diffraction analysis and an electron microscope made it possible to establish that the internal crystalline structure of the grain is not correct. In the crystal lattices of real metals, there are various defects (imperfections) that break bonds between atoms and affect the properties of metals. All lattice defects are violations of the stacking of atoms in the lattice. The arrangement of atoms in the lattice can be in the form of a centered cube (b- and c-iron, b-titanium, chromium, molybdenum, tungsten, vanadium), a cube whose faces are centered (r-iron, aluminum, copper, nickel, lead, c -cobalt) or hexagonal, or in the form of a cell (magnesium, zinc). Grains in polycrystals are not monolithic, but consist of separate subgrains, which are rotated relative to each other by a small angle. A subgrain is a polyhedron containing either a small number of dislocations or none at all. The main characteristics of subgrains: type, location, structure, dislocation density. Many dislocations are formed as a result of mechanical shear. The boundaries of subgrains and grains in metals are divided into low-angle and high-angle ones. Low-angle boundaries are observed between subgrains and have a dislocation structure. A low-angle boundary can be represented by a series of parallel edge dislocations. The formation of subgrains with low-angle dislocations is called polygonization. The structure of high-angle boundaries is more complex. Subboundaries are formed by certain systems of dislocations. Depending on what material and what effect the environment has on it, the location of dislocations is located. If the metal is slightly deformed, then the slip planes are the place of accumulation of dislocations. If, however, metals such as aluminum and iron are subjected to severe deformation, then dislocations are presented in the form of complex plexuses: spaces, networks. The structure, in which the subgrains are misoriented relative to each other at an angle of 15-300, is block or mosaic. The density of dislocations in a metal increases with an increase in the misorientation angle of subgrains and a decrease in their size. The atoms located at the grain boundaries and the atoms on the crystal surface, due to the uncompensated forces of interatomic interaction, have a higher potential energy compared to the atoms in the volume of subgrains. The presence of dislocations affects the strength properties of metals. According to theoretical calculations, the elastic limit of pure metals is 1000 times higher than the real one, and the elastic limit of steel is 100 times higher. 3. Light microscopy; quantitative characteristics of the microstructure A wide variety of methods are used to study the internal structure of alloys, most of which are based on physical principles. The study of the structure of metals begins with the help of a simple and common method in scientific and industrial laboratories - light microscopy (metallographic method). For the first time, the study of metals using a microscope was carried out by P.P. Anosov. He was engaged in the study of damask steel. Light microscopy is used to study the size, shape, arrangement of grains, defects in the crystalline structure (twins, dislocations), and it is also used to predict the behavior of metals under operating conditions. All metals are opaque substances (to visible light). The shape of the crystals, their size and location are studied on specially made microsections. In this case, a metal cut is made in the plane of interest to the researcher, the resulting plane is ground and polished. You can apply both coarse and fine grinding, in order to eliminate the unevenness of the surface of the section. Grinding is carried out before polishing. To obtain a flat surface, it is necessary to change the direction of movement of the samples by 90° when changing the abrasive. Grinding should be continued until the disappearance of the risks from the previous operation. According to the results of grinding, the surface roughness should be less than 0,08 microns. Polishing is carried out in order to obtain a mirror surface of the sample. Polishing can be mechanical, electrochemical and chemical-mechanical. Mechanical grinding is carried out using a machine with a rotating wheel, which is covered with polishing material. Abrasive particles are applied to this material. Chemical-mechanical polishing is carried out using abrasive particles and chemical elements. Electrochemical polishing is carried out in an electrolyte bath. Current is used to smooth the surface. During mechanical grinding and polishing, plastic deformation of the sample surface occurs. Depending on the hardness of the material, the depth of surface deformation can reach up to 25 microns. After grinding and polishing, the processed sample is immersed in water, then in alcohol, after which it is dried with filter paper. To reveal the structure, a relief is created or the structural components are painted in different colors, which is achieved by chemical etching. When etching, the acid acts on the grain boundaries, because there are places with a defective structure, which will become depressions in the etched section; the light falling on them is scattered and in the field of view of the microscope they will appear dark, and the body of the grain - light. To examine microsections in the study of the microstructure of metals, special microscopes are used in which the beam from the light source, reflected from the section, passes through the objective and the eyepiece, giving an appropriate magnification. The total magnification of a microscope is equal to the product of the magnifications of the objective and the eyepiece. Under a microscope on a microsection after polishing, you can see microcracks and non-metallic inclusions (graphite in cast irons, oxides). To reveal the very microstructure of the metal, the surface of the thin section is etched, i.e., it is treated with special reagents, the composition of which depends on the composition of the metal. The detection of the microstructure during etching is based on the fact that different phases are etched differently and colored differently. As a result of etching microsections of pure metals, it is possible to reveal the shape and size of individual grains. Microanalysis makes it possible to establish the size, shape and orientation of grains, individual phases and structural components, changes in the internal structure of metals and alloys depending on the conditions for their production and processing. In order to examine the details of the structure, an electron microscope is used, where the image is formed using a stream of fast-flying electrons. There are direct and indirect methods for studying the structure. Indirect methods are based on a special technique for preparing thin film impressions that reflect the relief of an etched section. By examining the resulting replica, the details of the structure are observed, their minimum size is 2–5 nm. Direct methods make it possible to study thin metal foils up to 300 nm thick in transmission using high-resolution electron microscopes (microscopes UEMV-100, UEMV-100A, UEMV-100V). An optical microscope is not an apparatus that can detect a crystal of any size. Quantitative metallography faces certain difficulties. Thus, the problem of determining the quantitative parameters of a three-dimensional object by studying its two-dimensional section is solved in several ways. Using the comparative method and the method of the average length of the segment crossing the grain, the size of the metal grains is determined. Today, an automated system for studying microsections of metals is used, which includes the use of a microscope, a video camera, a video blaster, and a personal computer. 4. Unit cell; coordination number; syngony Crystallographic directions and planes, anisotropy; interplanar distances A crystal lattice is an ordered arrangement of atoms. The unit cell of a crystal is the minimum volume of a crystal that completely preserves all its properties. The atoms in the lattice are arranged differently. The unit cell repeats itself in three dimensions and forms a crystal lattice. The structure of a crystal is determined by the position of the atoms in the unit cell. Coordination number - the total number of neutral molecules and ions that have a bond with the central ion in the complex. 1. The elements of the fourth group have a covalent saturated and directed bond, and each atom has four neighbors. The number of nearest neighbors is the coordination number. The elementary lattice is a tetrahedron with one atom in the center and four atoms at the vertices. 2. When an ionic bond is formed, the crystal lattices are more compact, the coordination number reaches 6 due to the unsaturation of the ionic bond. Example: the crystal lattice of NaCI is a primitive cube with chloride and sodium ions at the vertices. 3. Metal bonds make crystal lattices more compact. Coordination numbers reach values of 8 and 12. Three types of crystal lattices are formed in metallic materials: body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (HP). Syngony - one of the divisions of crystals on the basis of the symmetry of their elementary cell with the same systems of coordinate axes. Syngony characterizes the symmetry of three-dimensional structures with translational symmetry in three directions. Seven axial systems are distinguished depending on the length of the segments cut off on the crystallographic axes and the relative position of these axes. 1. Cubic syngony. Three equal axes intersect at right angles. 2. Tetragonal syngony. Two segments of the axis of the same length intersect at a right angle, the third axis is perpendicular to them, and the segment cut off on it is of a different length. 3. Rhombic syngony. Three axes of different lengths intersect at right angles. 4. Monoclinic syngony. Two axes of different lengths intersect at an oblique angle, the third axis makes a right angle with them. 5. Triclinic syngony. Three axes of different lengths intersect at oblique angles. 6. Trigonal syngony. Three segments of the axes of equal length intersect in one plane at an angle of 60 °C, the third axis is perpendicular to this plane, and the segment cut off on it has a different length. 7. Hexagonal syngony. The position of the axes is similar to their position in the trigonal syngony. The ordering of the arrangement of atoms in the crystal lattice makes it possible to single out individual crystallographic directions and planes. Crystallographic directions - direct rays coming from any reference point, along which atoms are located. The reference points are the vertices of the cube. Crystallographic directions - edges and diagonals of cube faces. There may be other directions. Crystallographic planes are planes on which atoms lie. Crystallographic directions and planes are characterized by Miller indices, which determine their various positions. Parallel planes in the crystal lattice, built identically, have the same indices. In order for the indices to be obtained from simple integers, the plane can be shifted in parallel. The position of any node of the crystal lattice relative to an arbitrarily chosen origin is determined by setting the coordinates x, y, z. For one elementary cell, these coordinates are equal to the lattice parameters a, b, c, respectively. To determine the index, find the coordinates of the atom closest to the reference point, lying in this direction, expressed in terms of the lattice parameter. All physical, including strength, properties of metals along different crystallographic directions depend on the number of atoms located in the mentioned directions. There are different numbers of atoms in the crystal lattice in different directions. In crystalline substances, anisotropy should be observed, i.e., unequal properties along different directions. Anisotropy - the result of an ordered arrangement of atoms in crystalline bodies, manifests itself within a single crystal. Real metals are polycrystalline bodies, including numerous grains arbitrarily oriented towards each other by their crystallographic directions and planes. The anisotropy of mechanical properties is observed when testing specimens cut along different crystallographic directions. Real metals have an average isotropy and are called quasi-isotropic or pseudo-isotropic bodies Interplanar distance - the shortest distance separating parallel and equally spaced nodal planes. 5. Classification of defects in the crystal structure. Point defects, dependence of their concentration on temperature. Edge and screw dislocations A single crystal can be grown from a liquid melt. A monocrystal is a piece of metal from a single crystal. Metals and alloys, which are obtained under normal conditions, consist of a large number of crystals and have a polycrystalline structure. These crystals are called grains and they are irregular in shape. Each grain has its own crystal lattice orientation, and it differs from the orientation of neighboring grains. The internal crystal structure of the grain is not correct. There are defects (imperfections) in the crystal lattices of metals that break bonds between atoms and affect the properties of metals. All lattice defects are violations of the stacking of atoms in the lattice. Surface imperfections are the boundaries of metal grains. The following structural imperfections are distinguished: lattice defect, point, small, linear, flat. Crystal defects significantly change the physical, mechanical, chemical, and technological properties of metals. Point defects include vacancies (empty sites), foreign interstitial atoms. The higher the temperature, the more defects. Impurity atoms are one of the most common imperfections in the crystal structure (vacancies, dislocated atoms). Vacancies are an empty node of the crystal lattice, which is formed due to various reasons. Sources of vacancies are grain boundaries in which the correct arrangement of atoms is violated. The number of vacancies and their concentration depend on the processing temperature. The number of vacancies increases with increasing temperature. Single vacancies are encountered when moving through the crystal and combine into pairs, forming divacancies, while their total surface decreases, the stability of the paired vacancy increases, and the formation of trivacancies and entire chains is possible. Dislocated atoms are atoms that have left the node of the crystal lattice and have taken a place in the interstices. Refers to point defects. Impurity atoms occupy the place of the main atoms in the crystal lattice or are introduced into the cell (a kind of point defects). If the correctness of the crystal structure around vacancies, dislocated atoms and impurity atoms is violated, then the balance of the force fields of atoms in all directions is also violated. All changes are no more than a few atomic diameters. Point defects interact with each other. There is an interaction of point defects and with linear defects - dislocations. Linear defects are small in two dimensions, in the third they are larger, which can be commensurate with the length of the crystal. Linear defects include chains of vacancies, interstitial atoms, and dislocations. Dislocations can be quite extended in one direction, and have a small extension in the opposite direction. The strength and ductility of metals directly depend on the presence of dislocations. Linear imperfections - dislocations, they are a special kind of imperfections in the crystal lattice. A characteristic of the dislocation structure is the density of dislocations. At present, various mechanisms of dislocation formation are known. Dislocations can arise during the growth of grains, during the formation of subgrains. It has been experimentally established that the boundaries of grains and blocks have a high density of dislocations. During crystallization from a melt, it is energetically favorable when the nucleus grows with the formation of a screw dislocation on its surface. Promote the formation of dislocations and segregation of impurities. In a solidified metal, dislocations arise as a result of the accumulation of vacancies. The region of crystal imperfection around the edge of the extraplane is called an edge (linear) dislocation. An edge dislocation represents a rapidly decaying field of elastic stresses in the crystal lattice around the edge of the extraplane, which is caused by the fact that above this edge the lattice parameters are somewhat compressed, and below, respectively, they are stretched. In one dimension, the length of the dislocation has a macroscopic character (a dislocation can break off only at the crystal boundary - it is the boundary of the shear zone). The motion of the edge dislocation is conservative. If the extraplane is in the upper part of the crystal, then the dislocation is called positive; if the extraplane is in the lower part of the crystal, then it is called negative. Screw dislocations are formed if two parts of the crystal are shifted towards the plane of the accumulation of vacancies. If a screw dislocation is formed by clockwise rotation, then it is called right, if counterclockwise - left. The vacancy and interstitial atoms do not flow to the screw dislocation. The formation of partial and mixed dislocations is also possible. The formation of dislocations increases the energy of the crystal. Dislocations contribute to an increase in internal stress in metals. The use of polarized light makes it possible to reveal the stress fields that arise around dislocations. 6. Diffusion in metals Diffusion is the transfer of matter due to the random thermal movement of diffusing particles. When a gas diffuses, its molecules change their direction of motion when they collide with other molecules. The main types of motion during diffusion in solids are random periodic jumps of atoms from a crystal lattice site to a neighboring site or vacancy. The development of the diffusion process leads to the formation of a diffusion layer, which is understood as a layer of the material of the part near the saturation surface, which differs from the initial one in chemical composition, structure and properties. The diffusion motion of any atom is a random walk due to the large amplitude of oscillations, which does not depend on the motion of other atoms, nor on the previous motion of this atom. Temperature-independent vibrations of atoms around the equilibrium position usually occur with a frequency of ~1013 с-1 The question of determining the diffusion mechanism is very complex. A major role in solving this problem was played by the works of Ya.I. Frenkel, which shows the enormous influence of defects in the crystal lattice, especially vacancies, on the process of diffusion movement of atoms. The most difficult is the simple exchange mechanism of diffusion, and the most probable is the vacancy mechanism. Each diffusion mechanism corresponds to a certain activation energy Q, i.e., the value of the energy barrier that an atom must overcome when moving from one position to another. Movement under the crowdion diffusion mechanism is similar to the propagation of a wave: each atom is displaced by a small amount, and the perturbation propagates rapidly. For diffusion, vacancies and their associations (bivacancies, vacancy-impurity atom complexes), as well as defects that are their sources (linear and surface) are of great importance. The main mechanism of self-diffusion and diffusion in substitutional solid solutions is the vacancy mechanism. In interstitial solid solutions, the main mechanism for the movement of small impurity atoms is interstitial. If two well-connected pieces of pure metals A and B are annealed for a long time, then mutual penetration of metals and a shift of the initial interface marked by inert marks (oxide particles or tungsten wires) by a value Δx will be observed, which is directly proportional to the square root of the annealing time. If DА > DВ, then component A penetrates into B at a faster rate than B into A, as a result of which part B of the sample increases in volume. Diffusion metallization is the process of diffusion saturation of the surface of products with metals or metalloids. Diffusion saturation is carried out in a powder mixture, gaseous medium or molten metal (if the metal has a low melting point). Boriding - diffusion saturation of the surface of metals and alloys with boron to increase hardness, corrosion resistance, wear resistance is carried out by electrolysis in molten boron salt. Boriding provides a particularly high surface hardness, wear resistance, increases corrosion resistance and heat resistance. Boron steels have high corrosion resistance in aqueous solutions of hydrochloric, sulfuric and phosphoric acids. Boriding is used for cast iron and steel parts operating under friction conditions in an aggressive environment (in chemical engineering). Chrome plating - diffusion saturation with chromium is carried out in powdered mixtures of chromium or ferrochrome with the addition of ammonium chromium (1%) and aluminum oxide (49%) at a temperature of 1000 ... 1050 ° C with an exposure of 6 ... 12 hours. Chrome plating is used for parts that work for wear in steam-water and aggressive environments (fittings, valves). During chromium plating of low-carbon steel products, the hardness increases and good corrosion resistance is acquired. Aluminizing is a process of diffusion saturation of the surface layer with aluminum, carried out in powdered mixtures of aluminum or in molten aluminum. The goal is to obtain high heat resistance of the surface of steel parts. Aluminizing is carried out in solid and liquid media. Siliconization - diffusion saturation with silicon is carried out in a gaseous atmosphere. The silicon-saturated layer of the steel part has not very high hardness, but high corrosion resistance and increased wear resistance in sea water, nitric acid, hydrochloric acid in sulfuric acid. Siliconized parts are used in the chemical, pulp and paper and oil industries. To increase the heat resistance, siliconization is used for products made of alloys based on molybdenum and tungsten, which have high heat resistance. In materials science, macro- and microscopic theories of diffusion are being developed. In macroscopic theory, emphasis is placed on formalism, that is, on thermodynamic forces and parameters. The microscopic theory uses mechanisms based on the theory of atomic jumps. 7. Phase transitions of the first and second kind The components in the liquid state (components A) are soluble indefinitely, the components in the solid state (components B) do not form chemical compounds and are insoluble. State diagrams represent a graph in the coordinates of the alloy - temperature, which reflects the products formed as a result of the interaction of the alloy components with each other under conditions of thermodynamic equilibrium at different temperatures. These are substances that, depending on temperature and composition, have a certain state of aggregation, a specific nature of the structure and certain properties, they are called phases. A phase is a homogeneous part of the alloy, which has the same composition, structure and properties. The liquid phase is a solution of molten components. Solid phases are grains that have a certain shape, size, composition, specific structure and properties. These are solid solutions, chemical compounds, as well as grains of pure components that do not form either solid solutions or chemical compounds with other components. The state diagram, which displays the limit state of alloys, can be divided into areas. Separate areas consist of one phase, and some - of two, they have different compositions, structures and properties. State diagrams contain information that is necessary to create and process alloys. State diagram of the first kind. Segment rule. This diagram covers alloys whose components form mixtures of their practically pure grains with negligible mutual solubility. The phase structure of the alloys in the diagram depends on the temperature. With the thermodynamic action of the components on each other, the temperature of their transition to the liquid state decreases. An alloy of two components that melt at a minimum temperature is called a eutectic or eutectic. The eutectic is a uniform mixture of simultaneously crystallized small grains of both components. The temperature at which both components melt simultaneously is called the eutectic temperature. The transition of alloys from a liquid state to a solid state during crystallization occurs in the temperature range lying between the liquidus line and the eutectic temperature, which corresponds to the solidus line. All quantitative changes in alloys during crystallization are subject to the rule of segments. Depending on the composition, all alloys are divided into hypoeutectic and hypereutectic. Hypoeutectic alloys contain component A over (100-Ve)%. In them, it is a redundant component. In hypereutectic alloys, component B is redundant (its amount exceeds Be). The amount of each structural component is calculated according to the rule of segments in relation to the eutectic temperature. State diagram of the second kind. Dendritic segregation. With unlimited solubility of components in each other, which have the same types of lattices and a similar structure of the outer electron shells, diagrams of the second kind are obtained. There are three phase regions in the diagram: 1. Above the liquidus line ADB is the region of the liquid phase G. 2. Below it, up to the solidus line ADB, there is a two-phase region b + G. Phase b is a solid solution of components A and B, the grains have a single crystal lattice. However, for alloys of different compositions, the number of atoms of components A and B in the unit cells of the lattice is different. 3. The area located under the solidus line is single-phase (phase b). Unlike alloys of mixtures of grains of practically pure components, each of the solidified alloys on the phase diagram represents a set of phase grains that do not differ from each other outwardly. In the case of accelerated cooling of the alloy during crystallization, diffusion processes do not have time to complete, and the central part of each grain is enriched with a more refractory component, and the peripheral part is enriched with a fusible component (A). This phenomenon is called dendritic segregation, which reduces the strength properties of alloys. Its prevention is possible due to the slow cooling of the alloy, which ensures its equilibrium crystallization. If dendritic segregation occurs, it is eliminated by prolonged diffusion annealing of the alloy. The diffusion processes that take place in this case equalize the chemical composition in the grains. During plastic deformation of a metallic material, an external force must overcome the resistance to the movement of dislocations, which is determined by the value of the Peierls-Nabarro force. This force depends on the intensity of interatomic interaction in the crystal lattice of the alloy. The atoms of the soluble component in the lattice of the solid solution form a stronger metallic bond with the atoms of the solvent component than in the lattices of both pure components. Because of this, the resistance to plastic deformation of a solid solution with an increase in the content of another component dissolved in it should increase according to a curvilinear law. 8. Melting of metals and structure of melts Melting is the physical process of the transition of a metal from a solid to a liquid molten state. Melting is a process that is the reverse of crystallization, occurs at a temperature above the equilibrium, i.e., during overheating. Since liquid metal has more internal energy than solid metal, heat is released during crystallization. There is a certain relationship between the heat Q and the crystallization temperature Tk. The degree of overheating during the melting of metals does not exceed a few degrees. In the liquid state, the atoms of a substance move randomly due to thermal motion, in the liquid there are groups of atoms of a small volume, within them the arrangement of atoms is similar to the arrangement in the crystal lattice. These groupings are unstable, they dissolve and reappear in the liquid. When the liquid is supercooled, some large groups become stable and capable of growth. These stable groups of atoms are called crystallization centers (nuclei). To carry out the melting process, it is necessary to have some overheating above the equilibrium temperature, i.e., a thermodynamic potential. Above the equilibrium temperature, a liquid metal is more stable, it has a smaller supply of free energy. Below this temperature, the solid metal is more stable. At equilibrium temperature, the free energies of the liquid and solid states are the same, therefore, at this temperature, both phases (liquid and solid) can coexist simultaneously and, moreover, for an infinitely long time. The equilibrium temperature is very close to the melting point Tm, with which it is often compared. Upon cooling, the transition from a liquid to a solid state is accompanied by the formation of a crystal lattice, i.e., crystallization. To induce crystallization, the liquid metal must be supercooled to a temperature below its melting point. Liquids at a temperature close to the melting point are called melts. Melts are metallic, ionic, semiconductor, organic and high polymer. Depending on what chemical compounds form melts, salt, oxide, oxide-silicate and other melts are isolated. Most melts contain skew-hedral particles. In the process of melting, chemical bonds in melts undergo modification. In semiconductors, the formation of metallic conductivity is observed; in some halides, instead of ionic conductivity, a decrease in electrical conductivity occurs due to the formation of a melt with a molecular composition. The temperature level also affects the type of bonding in melts. The average coordination number and interatomic distances are also characteristics of melts. In the process of melting metals, the coordination number decreases by about 10-15%. At the same time, the interatomic distances remain the same. When semiconductors are melted, their coordination number increases by a factor of 1,5, and the distance between atoms also increases. Multicomponent melts are characterized by non-equilibrium, metastable states, which are related to the structure of the initial solid phases. In many cases, there is a lag (hysteresis) in the properties of melts in the process of temperature change. The properties and structures of melts are influenced by the following factors: temperature, holding time, temperature fluctuation rate, the material from which the container is made, and the presence of impurities. The composition of the melts is distinguished by its complexity. Ionic melts can contain simple or complex ions, undissociated and polymeric molecules, as well as free volumes. Silicate melts may contain isolated silicon-oxygen tetrahedra and the chains, rings, networks, and frameworks they form. An unambiguous model of the structure of melts is rather difficult to form, since melts contain different types of particles and bonds. The main function of the models is the definition and interpretation of the properties of melts, as well as the calculation of properties. Melts in the metallurgical field are divided into intermediate, by-products and final products. Using melts as electrolytes, metals are produced and refined in metallurgy, as well as coatings are applied. Many alloys form as melts. Single crystals and epitaxial films are grown from melts. It is customary to use metal, salt and oxide melts as catalysts. Salt melts are used in annealing and hardening baths, high-temperature fuel cells, as heat carriers, fluxes in the process of soldering and welding metals, reaction media in inorganic and organic synthesis, as well as absorbers, extractants, etc. Some melts are used to obtain silicate , fluoride and other special stacks and amorphous metals. 9. Crystallization of metals; nucleation of crystals, critical germ; homogeneous and heterogeneous nucleation of crystals; crystal growth. Curves Tamman Crystallization is the process of transition of a metal from a liquid to a solid state with the formation of a crystalline structure. In nature, all spontaneous transformations, crystallization and melting, are due to the fact that the new state under new conditions is energetically more stable and has a smaller energy reserve. The transition of a metal from a liquid or vapor state to a solid state with the formation of a crystalline structure is called primary crystallization. The formation of new crystals in a solid crystalline substance is called secondary crystallization. The crystallization process consists of two simultaneous processes of nucleation and growth of crystals. Crystals can nucleate spontaneously - spontaneous crystallization or grow on existing ready-made crystallization centers - non-spontaneous crystallization. You can trace the process of metal crystallization using a time counter and a thermoelectric pyrometer. Two dissimilar wires, which are soldered at the ends, are immersed in molten metal and the resulting thermal current is proportional to the temperature of the metal, and the millivoltmeter needle deviates, it indicates the temperature on a specially graduated scale. The pyrometer readings are recorded in time and, according to the data obtained, cooling curves are built in the temperature-time coordinates. The critical point is the temperature that corresponds to any transformation in the metal. Upon cooling, the transition from a liquid to a solid state is accompanied by the formation of a crystal lattice, i.e., crystallization. In order to induce crystallization, the liquid metal must be supercooled to a temperature below its melting point. During solidification and during allotropic transformation in the metal, crystallization centers are first formed, around which atoms are grouped, forming the corresponding crystal lattice. The crystallization process consists of two stages: the formation of crystallization centers and the growth of crystals. In each of the emerging crystals, the crystallographic planes are randomly oriented, in addition, during primary crystallization, the crystals can rotate, since they are surrounded by liquid. Adjacent crystals grow towards each other, and their collision points define the boundaries of crystallites (grains). Amorphous substances have smooth cooling curves, without areas and ledges: it is clear that these substances cannot have allotropy. The mechanism of metal crystallization is that with a corresponding decrease in temperature inside the crucible with liquid metal, small crystals begin to form, called crystallization centers or nuclei. To start the growth of liquid metal crystals, it is necessary that the free energy of the metal decreased. If, as a result of the formation of a nucleus, the free energy of the metal increases, then the nucleus dissolves. The minimum size of a germ capable of growth is called the critical size of the germ, and such a germ is called stable. The greater the degree of supercooling, which lowers the free energy of the metal, the smaller the critical size of the nucleus. Crystals begin to grow around the formed centers. As crystals grow in the metal, which is still in the liquid state, new centers of crystallization continue to appear. Each of the growing new crystals is randomly oriented in space. Irregularly shaped crystals are called grains or crystals. Solids, including metals, consisting of a large number of grains, are called polycrystalline. D.V. Chernov established that the crystallization process consists of two elementary processes: the nucleation of crystallization centers and the growth of crystals from these centers. Much later, Tamman, studying the process of crystallization, established the dependence of the number of crystallization centers and the rate of crystal growth on the degree of supercooling. While the formed crystals grow freely, they have a more or less regular geometric shape. However, when growing crystals collide, their regular shape is violated, since the growth of faces stops in these areas. Growth continues in those directions where there is free access to the "feeding" fluid. As a result, growing crystals, which initially have a geometrically regular shape, after solidification, acquire an irregular external shape and are therefore called crystallites or grains. The growth of nuclei occurs as a result of the transition of atoms from a supercooled liquid to crystals. The crystal grows in layers, each layer has a one-atom thickness. There are two elementary processes of crystal growth. Formation of a two-dimensional embryo. Growth of a two-dimensional nucleus by supply of atoms from a supercooled liquid. After the formation of a two-dimensional nucleus on a flat face, further growth of a new layer proceeds relatively easily, since regions appear that are convenient for fixing atoms passing from the liquid. The size of the grains formed during crystallization depends not only on the number of spontaneously generated crystallization centers, but also on the number of particles of insoluble impurities that are always present in the liquid metal, which play the role of ready-made crystallization centers. 10. Ingot structure and amorphous alloys The structure of a steel ingot was first given in 1878 by D.K. Chernov. The structure of the cast ingot consists of three main zones. The first zone is the outer fine-grained crust, which consists of disoriented small crystals - dendrites. The second zone of ingots is the zone of columnar crystals. After the formation of the crust itself, the conditions for heat removal change, the temperature gradient decreases and the degree of steel supercooling decreases. The third zone of the ingot is the zone of equiaxed crystals. The crystals that form during the solidification of the metal have a different shape depending on the cooling rate, the nature and amount of impurities. More often, during the crystallization process, branched (tree-like) crystals are formed, which are called dendrites because of their shape, which resemble the shape of a tree. This form of crystals is explained by the fact that the nuclei that have arisen in the liquid metal grow in the direction with a minimum distance between atoms. This is how the axes of the first order are formed. Simultaneously with elongation of first-order axes, second-order axes nucleate and grow on their edges perpendicular to them at certain angles, from which third-order axes already grow and, ultimately, crystals in the form of dendrites are formed. The dendritic structure is revealed after special etching of thin sections, since all the gaps between the branches of the dendrites are filled, and usually only the junctions of the dendrites are visible in the form of grain boundaries. The correct shape of the dendrites is distorted as a result of the collision and accretion of particles in the later stages of the process. The dendritic structure is characteristic of the macro- and microstructure of cast metal (alloy). In contact with the cold wall of the mold, a zone of small equiaxed crystals is formed. The volume of solid metal is less than liquid, therefore, an air gap appears between the wall of the mold and the solidified metal; the wall itself heats up from contact with the metal. As a result, the rate of cooling of the metal decreases, the growth of crystals acquires a directional character - they grow from the wall of the mold to the center in the direction of heat removal and a zone of columnar crystals is formed. This phenomenon, as it were, of germination by long crystals of the thickness of the ingot is called transcrystallization. The resulting zone slows down the heat transfer to the outside, the cooling rate decreases and a zone of large unoriented crystals is formed. The liquid metal contains a certain amount of dissolved gases, therefore, in the volume of the ingot, when it is cooled, for metals that have a tendency to overcool, only ascending branches of the curves for the number of crystallization centers and the crystal growth rate are found. The size of the grains formed during crystallization depends not only on the number of spontaneously generated crystallization centers, but also on the number of particles of insoluble impurities that are always present in the liquid metal, which play the role of ready-made crystallization centers. Such particles can be oxides, nitrides, sulfides. Crystallization centers in a metal or alloy can be solid particles that have a small difference in the size of atoms with atoms of the base metal, their crystal lattice should be close in structure and parameters to the lattice of the crystallizing metal. The walls of molds and other forms where liquid metal crystallization occurs have irregularities and roughness. These irregularities affect the crystallization process by increasing the rate of crystallization. If the steel is not sufficiently deoxidized (the so-called boiling steel), then gas bubbles will form throughout the entire volume of the ingot. If the steel is well deoxidized (quiet steel), then it is cast into molds with an insulated profitable extension. In this place, the last portions of the liquid metal will crystallize. This is where gases will collect. This creates a large void, called a shrinkage cavity. Near the shrinkage cavity, the metal will be less dense, loose. Therefore, after rolling ingots of calm steel, the upper (profitable) part of the ingot (about 15-20% of the length of the ingot) is cut off. During rolling, the shape of the primary crystals of the cast metal changes. The dendrites are deformed, stretched along the direction of the metal flow, and turn into fibers. The joints of the crystals have a lower strength, therefore, along the fibers, the deformed steel has greater strength and toughness than across. Amorphous alloys are quite often brittle in tension, but relatively ductile in bending and compression, and can be subjected to cold rolling. Soft magnetic amorphous alloys come in three groups. 1. Based on iron (Fe81Si3 5B13 5C2) with high values of magnetic induction and low coercive force. 2. Based on cobalt (CO66Fe4(Mo, Si, B)30having a relatively low saturation induction, but high mechanical properties, low coercive force and high magnetic permeability. 3. Iron-nickel alloys (Fe40Ni40P14B6) with average magnetic induction and lower coercive force than iron alloys. Soft magnetic amorphous alloys are used in electrical engineering and the electronics industry. 11. Modification of metals. Standard tests for tensile, compression, bending, hardness, impact strength Modifiers can be added to the liquid metal in order to obtain the desired structure of the metal in castings. This is the modification process. According to the mechanism of influence on the crystallization process, modifiers can be divided into two groups: 1) modifiers, which are additional centers of crystallization; 2) modifiers - surfactants. These modifiers dissolve in the liquid metal. The crystallization process depends on the available crystallization centers. These centers are particles of refractory non-metallic inclusions, oxides, intermetallic compounds formed by impurities. By the beginning of the crystallization process, the centers are in the liquid metal and have the form of solid inclusions. During crystallization, metal atoms are deposited on the activated impurity surface. This crystallization is called heterogeneous, in which the walls of the mold play the role of nuclei. Upon solidification, the presence of ready-made centers of crystallization leads to a decrease in the size of the crystals. The effect of structure refinement increases when the structural and dimensional correspondence of the impurity phase with the base metal is observed, which contributes to the conjugation of their crystal lattices. The liquid metal contains dissolved impurities that cause structure refinement. Being adsorbed, they reduce the surface tension at the liquid-solid interface and the linear growth rate of crystals. The refinement of the structure contributes to the improvement of the mechanical properties of the metal. To refine the structure of alloys, a technological operation is used - modification. This operation consists in introducing special additives - modifiers into the liquid alloy before pouring. For this, surfactants are used, as well as elements that form refractory fine particles. Modifiers are added to alloys. An increase in the temperature of the liquid metal before pouring leads to coarsening of the grain during crystallization and, conversely, a decrease in the grain size occurs as a result of cooling the metal. Chilling is effective in the presence of modifiers that form phases together with structural and dimensional correspondence with the base metal. Standard tests Static tensile testing is a method of mechanical testing of metals. For static tests, round specimens of the tested metal or flat specimens for sheet materials are made. The samples consist of a working part and heads, which are designed to be fixed in the grips of a tensile testing machine. Sample sizes are standardized. When stretched, the specimen elongates. Some metal alloys have a linear expansion coefficient close to zero (used for the manufacture of precision instruments, radio tubes). A round or flat sample of standard sizes is installed in the clamps of the tensile testing machine, and increasing the load, the change in its length is monitored. The writing device of the machine records the stretch diagram, which determines the mechanical properties. Hardness - the property of a material to resist contact deformation, the ability of a material to resist penetration into its surface of a solid body - an indenter. Indenter - diamond tip in the form of a cone. Hardness testing is the most accessible type of mechanical testing. Hardness tests are carried out quickly and do not require complex samples; they allow one to judge other mechanical properties of metals (for example, tensile strength). Hard tip indentation methods are common. Determination of hardness by the Rockwell method. A steel or diamond cone with an angle of 120° or a steel hardened ball with a diameter of 1,59 mm is pressed into the surface of the test specimen, and the hardness of the material is estimated from the depth of penetration into the surface. Three scales are applied on the Rockwell hardness tester: A (black) - the test is carried out with a diamond cone, hardness is indicated by HRA; B (red) - the test is carried out with a ball, the hardness is indicated by H13B; C (black) - the test is carried out with a steel cone, the hardness is indicated by HRC. Determination of hardness by the Vickers method. A tetrahedral diamond pyramid is pressed into the surface of the sample, and the hardness is determined along the diagonal of the imprint. The Vickers method makes it possible to measure the hardness of soft and hard metals and alloys and the hardness of thin surface layers. Impact tests measure the ability of a metal to resist impact loads that machine parts are subjected to during operation. Impact tests are carried out on standard-shaped specimens on instruments called pendulum impact testers. Impact strength - the work spent on the impact fracture of the sample and related to its cross-sectional area at the notch. Impact testing is carried out to assess the propensity of materials to brittle fracture. Bending is a softer way of loading than tension. Low-plastic materials are tested for bending. Tests are carried out on samples of large length, cylindrical or rectangular shape. They are installed on two supports. The determined characteristics are tensile strength and deflection. 12. Phase transformations in the solid state A phase is a homogeneous part of the system, which is separated from another part of the system (phase) by an interface, when passing through which the chemical composition or structure changes abruptly. During the crystallization of a pure metal, there are two phases in the system: liquid (molten metal) and solid (grains of solidified metal). In hard alloys, phases can be pure metal grains, solid solution grains, and chemical compound grains. Many metals in the liquid state dissolve one into another in any ratio. As a result of dissolution, a homogeneous liquid solution is formed with a uniform distribution of atoms of one metal among the atoms of another metal. Due to this interaction, in practice, in order to uniformly distribute the substances in the alloy, they resort to their melting. Some metals, which differ greatly in atomic size, do not dissolve in the liquid state, while other metals dissolve in the liquid state to a limited extent. In the formation of alloys during their solidification, various interactions of the components are possible. If in the process of crystallization the force of interaction between homogeneous atoms is greater than the force of interaction between heterogeneous atoms, then after crystallization a mechanical mixture is formed, consisting of grains of pure metals. In this case, grains of one pure metal and next to them grains of another pure metal will be present in the hard alloy. This form of interaction occurs when there is a large difference in the properties of the metals included in the alloy. Another form of interaction between the substances that make up the alloy is the formation of solid solutions. Solid solutions are solid phases in which the ratios between the components can change. In a solid solution, just as in pure metals, the atoms in space are regularly arranged and form a crystal lattice. This is what distinguishes them from liquid solutions. In a solid solution, one of the substances that make up the alloy retains its crystal lattice, and the second substance, which has lost its crystal structure, is distributed in the form of individual atoms in the crystal lattice of the first. The first substance is a solvent, and the second is soluble. Depending on the nature of the distribution of atoms of a soluble element, solid solutions of interstitial, substitution, and subtraction are distinguished; regardless of the type of solid solution, they have in common that they are single-phase and exist in a range of concentrations. Solid solutions are characterized by a metallic type of bond. Some metalloids - hydrogen, nitrogen, carbon, boron, which form interstitial solid solutions with metals - have the smallest atomic sizes. But even for these elements, the size of atoms somewhat exceeds 12b the size of interatomic gaps in the crystal lattice of metals, therefore, when interstitial solid solutions are formed, the lattice is distorted and stresses arise in it. In this case, the concentration of the interstitial solid solution cannot be high. It rarely exceeds 1-2%. In substitutional solid solutions, the atoms of the soluble element take the place of the atoms of the base metal. Foreign atoms can replace the atoms of the solvent in any place, so such solutions are called disordered solid solutions. The sizes of the atoms of a soluble element always differ from the sizes of the solvent atom (they are larger or smaller), therefore, when a substitutional solid solution is formed, the crystal lattice of the solvent metal is distorted without losing its basic structure. Substitution solid solutions can be limited and unlimited. One of the conditions for unlimited solubility is the size factor. The greater the difference in atomic radii, the lower the solubility. With a decrease in temperature in substitutional solid solutions, a process of redistribution of atoms occurs, as a result of which the atoms of the dissolved element will occupy strictly defined places in the solvent lattice. Such solid solutions are called ordered solid solutions, and their structure is called a superstructure. Some elements modify their crystalline structure depending on changes in external conditions - temperature and pressure. In the solid state, lithium and molybdenum have a body-centered cubic lattice; aluminum, silver, gold, platinum - face-centered, and magnesium, zirconium - hexagonal. When the temperature changes, it may turn out that for the same metal a different lattice will be more stable than the one that was at a different temperature. This phenomenon is called polymorphism. Each type of lattice represents an allotropic modification or modification. In polymorphic transformations of metals, temperature is of primary importance. The transformation of one allotropic form into another occurs at a constant temperature, called the polymorphic transformation temperature, and is accompanied by a thermal effect, similar to the phenomena of melting-solidification or evaporation-condensation. This is due to the need to spend a certain amount of energy on the rearrangement of the crystal lattice. 13. Elastic and plastic deformation of metals Deformation is a change in the shape and size of the body, deformation can be caused by the influence of external forces, as well as other physical and mechanical processes that occur in the body. Deformations include such phenomena as shear, compression, tension, bending and torsion. Elastic deformation is a deformation that disappears after the load is removed. Elastic deformation does not cause residual changes in the properties and structure of the metal; under the action of the applied load, an insignificant reversible displacement of atoms occurs. When a single crystal is stretched, the distances between atoms increase, and when compressed, the atoms approach each other. When the atoms are displaced from the equilibrium position, the balance of the forces of attraction and electrostatic repulsion is disturbed. After the load is removed, the displaced atoms, due to the action of attractive or repulsive forces, return to their original equilibrium state and the crystals acquire their original dimensions and shape. The deformation can be elastic, disappearing after the load is removed, and plastic, remaining after the load is removed. The smallest stress causes deformation, and the initial deformations are always elastic and their magnitude is directly dependent on the stress. The main mechanical properties are strength, plasticity, elasticity. Plasticity is important, it determines the possibility of manufacturing products by various methods of pressure treatment. These methods are based on the plastic deformation of the metal. Materials that have increased plasticity are less sensitive to stress concentrators. For this, a comparative assessment of various metals and alloys is carried out, as well as their quality control in the manufacture of products. The physical nature of the deformation of metals Under the action of stresses, a change in the shape and size of the body occurs. Stresses arise when external forces of tension, compression act on the body, as well as as a result of phase transformations and some other physicochemical processes that are associated with a change in volume. A metal that is in a stressed state, under any kind of stress, always experiences normal and tangential stresses, deformation under the action of stresses can be elastic and plastic. Plastic occurs under the action of shear stresses. Elastic - this is such a deformation, which, after the termination of the action that caused the stress, disappears completely. During elastic deformation, there is a change in the distances between atoms in the crystal lattice of the metal. With an increase in interatomic distances, the forces of mutual attraction of atoms increase. When the stress is removed under the action of these forces, the atoms return to their original position. The lattice distortion disappears, the body completely restores its shape and dimensions. If the normal stresses reach the value of the forces of interatomic bonding, then brittle fracture will occur by separation. Elastic deformation is caused by small tangential stresses. Plastic deformation is the deformation that remains after the termination of the action of the stresses that caused it. During plastic deformation in the crystal lattice of a metal, under the action of tangential stresses, an irreversible displacement of atoms occurs. At low voltages, the atoms are slightly displaced and, after the stress is removed, they return to their original position. With an increase in shear stress, an irreversible displacement of atoms by the lattice parameter is observed, i.e., plastic deformation occurs. With an increase in shear stresses above a certain value, the deformation becomes irreversible. When the load is removed, the elastic component of the deformation is eliminated. Part of the deformation, which is called plastic, remains. During plastic deformation, the structure of the metal and its properties change irreversibly. Plastic deformation is carried out by slip and twinning. Sliding in the crystal lattice proceeds along planes and directions with dense packing of atoms, where the shear resistance is the lowest. This is explained by the fact that the distance between adjacent atomic planes is the greatest, i.e., the connection between them is the smallest. The sliding planes and the sliding directions lying in these planes form a sliding system. In metals, one or several slip systems can act simultaneously. Metals with a cubic crystal lattice (fcc and bcc) have high plasticity, sliding in them occurs in many directions. The sliding process should not be represented as the simultaneous movement of one part of the crystal relative to another, it is carried out as a result of the movement of dislocations in the crystal. The displacement of a dislocation in the slip plane MM through the crystal leads to a displacement of the corresponding part of the crystal by one interplanar distance, and a step is formed on the right side of the crystal surface. 14. Types of fracture: concepts of ductile and brittle fracture Fatigue is the destruction of metals under the action of repeated loads. It occurs at the springs of automation. Most part failures are caused by material fatigue. Fatigue failure develops in parts operating at stresses less than the yield strength of the material. Elastic-plastic deformation, when sufficiently high stresses are reached, can result in the destruction of the body. The destruction process consists of several stages: the initiation of microcracks, the formation of macrocracks, and the propagation of a macrocrack over the entire section of the body. In general, a distinction is made between ductile and brittle fractures. The type of destruction depends on many factors: the composition of the metal, its structural state, loading conditions and temperature. The type of fracture, ductile or brittle, is determined by studying fractures. Brittle fracture is characterized by a brook fracture. Ductile fracture occurs by shearing under the action of shear stresses and is accompanied by significant plastic deformation. Ductile fracture is characterized by a fibrous (matte) fracture of a part or sample. Brittle fracture occurs under the action of normal tensile stresses, causing separation of one part of the body from another without noticeable traces of macroplastic deformation. Brittle fracture is characterized by a crystalline (shiny) fracture. Brittle fracture is preceded by plastic deformation until a critical size crack is reached and then by brittle dislocation-free fracture. Brittle fracture is a spontaneous process. The occurrence of microcracks in ductile and brittle fractures occurs through the accumulation of dislocations in front of grain boundaries or other obstacles (non-metallic inclusions, carbide particles, interphase boundaries), which leads to stress concentration. When analyzing the microstructure, transcrystalline (along the body of the grain) and intercrystalline (along the grain boundaries) destruction are distinguished. The destruction of metal under the operating conditions of structures and machines can be not only ductile or brittle, but also mixed - ductile-brittle. Materials are destroyed differently in cases of fatigue and under single loads. Fracture is characterized by the absence of external signs of plastic deformation in a fracture, i.e., in general, a fatigue fracture has the character of a brittle fracture. However, in microvolumes and thin layers of the cross section of a loaded sample, there may be plastic deformations that lead to the initiation of cracks. These cracks, gradually developing and propagating, lead to the final destruction of the material. In the case of fatigue loading, the onset of plastic deformation caused by the motion of dislocations can be at stresses below the yield point. With an increase in the number of loading cycles, the density of dislocations increases, primarily in the surface layers. Thin slip lines on the surface turn into characteristic stripes, the profile of which is presented in the form of protrusions and depressions. The depth of the cavities, depending on the test time, can reach 10-30 µm. During the formation of stable slip bands, regions with high and low dislocation densities alternate. Fatigue cracks originate in surface depressions. One of the possible mechanisms for the formation of protrusions and cavities is associated with the circular motion of screw dislocations. A screw dislocation moves from one plane to another along a closed contour with the help of transverse slip. As a result, the dislocation reaches the surface, on which protrusions and depressions are formed. Microcracks under cyclic loading are nucleated at the initial stage of testing due to the influx of vacancies and subsequent formation and coalescence of micropores. A large number of microcracks can form in the sample. But in the future, not all microcracks develop, but only those that have the sharpest peaks and are most favorably located in relation to the acting stresses. The longest, sharpest and deepest crack, which propagates over the sample cross section, leads to the final destruction of the sample: the presence of a zone of progressively growing crack and a zone of final fracture is typical for the fatigue fracture of the sample. In the zone of a progressively growing crack, stripes in the form of curved lines are observed. The bands are formed as a result of jerks and delays in the movement of a crack due to hardening of the metal at its base and expansion of its front. The process of destruction under cyclic loads is significantly affected by stress concentrators. Stress concentrators can be constructive (sharp transitions from section to section), technological (scratches, cracks, risks from the cutter), metallurgical (pores, shells). Regardless of their origin, stress concentrators to some extent reduce the endurance limit at the same level of alternating stresses. To assess the effect of a stress concentrator on fatigue, smooth and notched specimens are tested under a symmetrical stress cycle. The incision on the sample is made in the form of a sharp circular undercut. 15. Electrical properties of conductor materials Pure metals and metal alloys are used as conductor materials. Pure metals have the highest conductivity, with the exception of mercury. Winding, installation, installation cables and wires are made from copper and aluminum. Aluminum belongs to the group of light metals. Its density is 2,7 g/cm3. Availability, high conductivity, and resistance to atmospheric corrosion have allowed aluminum to be widely used in electrical engineering. The disadvantages of aluminum are low mechanical tensile strength and increased softness even in hard-drawn aluminum. Aluminum is a silver-colored or silver-white metal. Its melting point is 658-660 °C. Bare aluminum wires can work for quite a long time due to the fact that aluminum is covered with a thin oxide film in a short time. This serves as protection against oxygen. The oxide film on aluminum wires has a significant electrical resistance, and therefore large transient resistances are formed at the junctions of aluminum wires. The joints are cleaned using petroleum jelly to prevent the effect of oxygen on aluminum. When wetting the junctions of aluminum wires with other wires from other metals (copper, iron) obtained mechanically (bolted connections), galvanic pairs are formed with a certain electromotive force. In this case, the aluminum wire under the influence of local current will be destroyed. In order to prevent the formation of galvanic vapors in a humid atmosphere, the junctions with other wires made of other metals must be carefully protected from moisture by varnishing and other methods. Nitrogen oxides (NO), chlorine (Cl), sulfur dioxide (SCy, hydrochloric and sulfuric acids and other agents) cause direct corrosion of aluminum. Reliable wire connections to each other, as well as to wires from other metals, are carried out using cold or hot welding. The higher the chemical purity of aluminum, the better it resists corrosion.Therefore, the purest grades of aluminum with a pure metal content of 99,5% are used for the manufacture of electrodes in electrical capacitors, for the manufacture of aluminum foil and winding wires of small diameters of 0,05-0,08 mm Conductive aluminum is used, containing at least 99,7% pure metal. Aluminum is used for the manufacture of wire with a pure metal content of at least 99,5%. Aluminum wire is produced by drawing and rolling. There are three types of aluminum wire: AM (soft annealed), APT (semi-hard) and AT (hard unannealed). The wire is produced with a diameter of 0,08 to 10 mm. Semiconductors make up a vast area of materials that differ from each other in a wide variety of electrical and physical properties, as well as a large variety of chemical composition, which determines various purposes in their technical use. According to their chemical nature, semiconductors can be divided into the following four main groups. 1. Crystalline semiconductor materials built from atoms and molecules of one element. 2. Oxide crystalline semiconductor materials, that is, materials from metal oxides. 3. Crystalline semiconductor materials based on compounds of atoms of the third and fifth groups of the system of elements of the periodic table. 4. Crystalline semiconductor materials based on compounds of sulfur, selenium, copper, lead - they are called sulfides, selenides. Silicon carbide belongs to the first group of semiconductor materials and is the most common single-crystal material. This semiconductor material is a mixture of many small crystals, randomly soldered to each other. Silicon carbide is formed at high temperature when graphite and silicon are combined. It is used in photocells, diodes. The possibility of increasing the operating temperature of the insulation is very important for practice. In electrical machines and apparatuses, an increase in heating, which is usually limited precisely by electrical insulation materials, makes it possible to obtain more power with the same dimensions, or, while maintaining power, reduce the size and cost of the product. GOST provides for the division of electrical insulating materials for electrical machines, transformers and apparatus into heat resistance classes, for which the highest permissible operating temperatures are fixed when these materials are used in general-purpose electrical equipment that operates for a long time under normal operating conditions for this type of electrical equipment. At these temperatures, reasonable service life of electrical equipment is ensured. Class Y includes fibrous materials based on cellulose and silk (yarn, fabrics, tapes, papers, cardboards, wood, etc.), unless they are impregnated and immersed in a liquid electrical insulating layer. 16. Methods for determining electrical properties Metals with high electrical conductivity (copper, aluminum) are used in electrical engineering, for the installation of power lines, and alloys with high electrical resistance - for incandescent electric heaters. Thermal properties of dielectrics: heat resistance, cold resistance, thermal conductivity, thermal expansion. Heat resistance - the ability of electrical insulating materials and products without harm to them for some time to withstand exposure to high temperatures. The heat resistance of inorganic dielectrics is determined by the beginning of a significant change in electrical properties. And the heat resistance of organic dielectrics is determined by the onset of mechanical tensile or bending deformations, the immersion of the needle into the material under pressure when heated, and by electrical characteristics. Thermal aging of insulation is a deterioration in the quality of insulation, determined by prolonged exposure to elevated temperatures. The aging rate is affected by the temperature at which the insulation of electrical machines and other electrical insulating structures operates. The rate of aging is also influenced by changes in air pressure or oxygen concentration, the presence of ozone, chemical reagents that slow down or accelerate aging. Thermal aging is accelerated by exposure to ultraviolet rays, by exposure to an electric field, mechanical stress. GOST provides for the division of electrical insulating materials for electrical machines, transformers and apparatuses into heat resistance classes. At acceptable temperatures, reasonable service life of electrical equipment is ensured. Class Y: Cellulose and silk based fibrous materials not impregnated or immersed in a liquid electrical insulating layer. Class A: organic fibrous materials working with impregnated varnishes and immersed in liquid electrical insulating material, i.e. protected from atmospheric oxygen. Class E: plastics with organic filler and thermosetting binder such as phenol-formaldehyde and similar resins, insulation of enameled wires on polyurethane and epoxy varnishes. Classes Y, A, E include purely organic electrical insulating materials. The dielectric strength is determined by the breakdown voltage related to the dielectric current at the breakdown site. The breakdown of liquid dielectrics occurs as a result of ionization thermal processes. The main breakdown factor is the presence of foreign impurities. The presence of impurities makes it difficult to create a breakdown theory for these substances. Therefore, the ideas of the theory of electrical breakdown are applied to liquids that are maximally purified from impurities. At high electric field strengths, electrons can be ejected from the metal of the electrodes and the molecules of the liquid itself can be destroyed due to impacts with charged particles. In this case, the greater dielectric strength of liquid dielectrics compared to gaseous dielectrics is explained by the significantly shorter electron mean free path. The breakdown of liquids containing gas inclusions is explained by local overheating of the liquid (due to the energy released in relatively easily ionized gas bubbles), which leads to the formation of a gas channel between the electrodes. The presence of water in a liquid dielectric reduces its dielectric strength. Water at normal temperature is contained in the dielectric in the form of tiny droplets. Under the influence of an electric field, the droplets are polarized and create chains with increased conductivity between the electrodes, along which an electrical breakdown occurs. A peculiar dependence of the electrical strength of a liquid dielectric containing water on temperature is observed. As the temperature rises, water passes into the state of a molecular solution, in which it has little effect on the electrical strength. The electrical strength of the liquid dielectric increases to a certain maximum. A further decrease in electrical strength is explained by the phenomena of liquid boiling. An increase in the electrical strength of transformer oil at low temperatures is associated with an increase in the viscosity of the oil and lower values of the dielectric constant of ice compared to water. Solid inclusions (soot, fibers) distort the electric field inside the liquid and also lead to a decrease in the electrical strength of dielectric liquids. Purification of liquid dielectrics from impurities significantly increases the dielectric strength. For example, unrefined transformer oil has an electrical strength of approximately 4 MV/m; after thorough cleaning, it rises to 20-25 MV / m. The breakdown of liquid dielectrics, as well as gases, is affected by the shape of the electrodes: with an increase in the degree of inhomogeneity of the electric field, the breakdown voltage at the same distances decreases. In inhomogeneous electric fields, as well as in gases, there may be an incomplete breakdown - a corona. Long-term corona in liquid dielectrics is unacceptable, since it causes decomposition of the liquid. The frequency of the current affects the dielectric strength. 17. Heat capacity and thermal conductivity of metals and alloys Heat capacity is the ability of a substance to absorb heat when heated. Its characteristic is the specific heat capacity - the amount of energy absorbed by a unit of mass when heated by one degree. The possibility of cracks in the metal depends on the magnitude of thermal conductivity. If the thermal conductivity is low, then the risk of cracking increases. Thus, alloyed steels have a thermal conductivity that is five times less than that of copper and aluminum. The size of the heat capacity affects the level of fuel consumed to heat the billet to a certain temperature. For metal alloys, the specific heat capacity is in the range of 100-2000 J / (kg * K). For most metals, the heat capacity is 300-400 J / (kg * K). The heat capacity of metallic materials increases with increasing temperature. Polymeric materials, as a rule, have a specific heat capacity of 1000 J/(kg·K) or more. The electrical properties of materials are characterized by the presence of charge carriers of electrons or ions and their freedom of movement under the action of an electric field. The high energies of covalent and ionic bonds impart dielectric properties to materials with these types of bonds. Their weak electrical conductivity is due to the influence of impurities, and under the influence of moisture, which forms conductive solutions with impurities, the electrical conductivity of such materials increases. Materials with different types of bonds have different temperature coefficients of electrical resistance: for metals it is positive, for materials with covalent and ionic bonds it is negative. When metals are heated, the concentration of charge carriers - electrons does not increase, and the resistance to their movement increases due to an increase in the amplitudes of atomic vibrations. In materials with a covalent or ionic bond, when heated, the concentration of charge carriers increases so much that the effect of interference from an increase in atomic vibrations is neutralized. Thermal conductivity is the transfer of thermal energy in solids, liquids and gases with macroscopic immobility of particles. Heat transfer occurs from hotter particles to colder ones and obeys the Fourier law. Thermal conductivity depends on the type of interatomic bond, temperature, chemical composition and structure of the material. Heat in solids is transferred by electrons and phonons. The mechanism of heat transfer is primarily determined by the type of bond: in metals, heat is transferred by electrons; in materials with a covalent or ionic type of bond - phonons. Diamond is the most thermally conductive. In semiconductors, at a very low concentration of charge carriers, thermal conductivity is carried out mainly by phonons. The more perfect the crystals, the higher their thermal conductivity. Single crystals conduct heat better than polycrystals, since grain boundaries and other defects in the crystal structure scatter phonons and increase electrical resistance. The crystal lattice creates a periodic energy space in which the transfer of heat by electrons or phonons is facilitated compared to the amorphous state. The more impurities the metal contains, the finer the grains and the more distorted the crystal lattice, the lower the thermal conductivity. The larger the grain size, the higher the thermal conductivity. Doping introduces distortion into the crystal lattices of solid solutions and lowers the thermal conductivity compared to pure metal - the basis of the alloy. Structural components representing dispersed mixtures of several phases (eutectics, eutectoids) reduce thermal conductivity. Structures with a uniform distribution of phase particles have a lower thermal conductivity than the alloy base. The limiting type of such a structure is a porous material. Compared to solids, gases are thermal insulators. Graphite has a high thermal conductivity. When heat is transferred parallel to the layers of carbon atoms of the basal plane, the thermal conductivity of graphite exceeds the thermal conductivity of copper by more than 2 times The branched graphite plates in gray cast iron have a single crystal structure and therefore it has a high thermal conductivity. Ductile cast iron with nodular graphite with the same volume fraction of graphite has a thermal conductivity of 25...40 W/m*K, which is almost half that of gray cast iron. When heated, the thermal conductivities of steels of different classes converge. Glass has a low thermal conductivity. Polymeric materials conduct heat poorly; the thermal conductivity of most thermoplastics does not exceed 1,5 W/(mOK). The thermal conductivity can change in the same way as the electrical conductivity if the electronic thermal conductivity of the metal is le. Then any changes occurring in the chemical and phase composition and structure of the alloy affect the thermal conductivity as well as the electrical conductivity (according to the Wiedemann-Franz rule). As the composition of the alloy moves away from the pure components, the thermal conductivity decreases. The exception is, for example, copper-nickel alloys, in which the opposite phenomena occur. 18. Dilatometry. Magnetic properties of metals and alloys. Methods of determination Dilatometry - branch of physics; main task: study of the influence of external conditions (temperature, pressure, electric, magnetic fields, ionizing radiation) on the dimensions of bodies. The main subject of study: the thermal expansion of bodies and the resulting anomalies. dilatometric method. When metals and alloys are heated, the volume and linear dimensions of the body change - thermal expansion. If these changes are due only to an increase in the energy of atomic vibrations due to an increase in temperature, then when the temperature returns to the previous level, the original dimensions of the body are also restored. If phase transformations occur in the body during heating (or cooling), then the changes in size can be irreversible. Changes in the size of bodies associated with heating and cooling are studied on special devices - dilatometers. The dilatometric method is a method by which the critical points of metals and alloys are determined, the processes of decomposition of solid solutions are studied, and the temperature intervals for the existence of hardening phases are established. The advantage of these instruments is their high sensitivity and independence of readings from the rate of temperature change. The high sensitivity of electrical measurement methods is widely used in the study of phase transformations, fine structure defects, and other phenomena occurring in metals and alloys that cannot be studied by other research methods. Electrical resistance is measured using various bridge circuits, as well as compensation methods. Various methods of magnetic analysis are used in the study of processes associated with the transition from the paramagnetic state to the ferromagnetic state (or vice versa), and it is possible to quantify these processes. Magnetic analysis is widely used in solving problems of practical metallurgy, such as studying the effect of heat treatment, deformation, and alloying on the structure. It is also possible to use magnetic analysis to solve some more complex problems of physical metallurgy. The method of internal friction is based on the study of irreversible energy losses of mechanical vibrations inside a solid body. Using this method, it is possible to calculate diffusion coefficients with high accuracy, including at low temperatures, where no other method is applicable; determine the change in the concentration of solid solutions; distribution of impurities; obtain information about phase and polymorphic transformations and changes in the dislocation structure. Hard magnetic steels and alloys are used to make permanent magnets. For permanent magnets, high-carbon steels with 1% C, alloyed with chromium (3%) EX3, as well as simultaneously with chromium and cobalt, EX5K5, EX9K15M2, are used. Alloying elements increase the coercive and magnetic energy. Alnico-type alloys are widely used in industry. Alloys are hard, brittle and not deformable, so magnets are made from them by casting, then grinding is carried out. Materials are divided into diamagnets, paramagnets and ferromagnets, depending on the degree of their magnetic susceptibility and what their sign is. Diamagnets have a negative magnetic susceptibility. Their magnetization is directed opposite to the applied magnetic field. This leads to a weakening of this field. Semiconductors (Si, Ge), dielectrics (polymers), some non-transition metals (Be, Cu, Ag, Pb) are diamagnets. Paramagnets have low magnetization, which occurs under the influence of an external field. Paramagnets are K, Na, Al and transition metals Mo, W, Ti. Ferromagnets are characterized by high magnetic susceptibility. These include: iron, cobalt, nickel and gadolinium. Characteristics: residual induction Vg, coercive force Hc and magnetic permeability m = V/N. Residual induction - magnetic induction, which remains in the sample as a result of its magnetization and further demagnetization. Coercive force - the magnetic field strength of the opposite sign, applied to the sample in order to demagnetize it. Magnetic permeability is the main characteristic of the magnetization intensity. Having determined the tangent of the slope angle to the primary magnetization curve B = f(H), one can calculate the magnetic permeability. The YUNDK15 alloy contains 18–19% Ni, 8.5–9.5% Al, 14–15% Co, and 3–4% Cu. Soft magnetic steels (electrical steel) (1212, 1311, 1511, 2011, 2013, 2211, 2312, 2412, 3415, 3416, 79NM, 81NMA) are used for the manufacture of DC and AC magnetic circuits. They are intended for the manufacture of armatures and poles of DC machines, rotors and stators of asynchronous motors, etc. Paramagnetic steels (17Kh18N9, 12Kh18N10T, 55G9N9Kh3, 40G14N9F2, 40Kh14N9Kh3YuF2, etc.) are required in electrical engineering, instrument making, shipbuilding and special areas of technology. The disadvantage of these steels is their low yield strength (150-350 MPa), which makes it difficult to use them for highly loaded machine parts. 19. The value of mechanical and physical properties in the operation of products Properties as indicators of material quality The properties of metals are divided into physical, chemical, mechanical and technological. Physical properties include: color, specific gravity, fusibility, electrical conductivity, magnetic properties, thermal conductivity, heat capacity, expandability when heated. To chemical - oxidizability, solubility and corrosion resistance. To mechanical - strength, hardness, elasticity, viscosity, plasticity. To technological - hardenability, fluidity, ductility, weldability, machinability. The strength of a metal is its ability to resist the action of external forces without collapsing. Hardness is the ability of a body to resist the penetration of another, more solid body into it. Elasticity - the property of a metal to restore its shape after the termination of the action of external forces that caused a change in shape (deformation). Viscosity is the ability of a metal to resist rapidly increasing (shock) external forces. Viscosity is the opposite property of brittleness. Plasticity is the property of a metal to be deformed without destruction under the action of external forces and to retain a new shape after the cessation of the forces. Plasticity is the opposite property of elasticity. Modern methods of testing metals are mechanical tests, chemical analysis, spectral analysis, metallographic and X-ray analysis, technological samples, flaw detection. These tests provide an opportunity to get an idea of the nature of metals, their structure, composition and properties, as well as to determine the good quality of finished products. Mechanical testing is of the utmost importance in industry. Details of machines, mechanisms and structures work under loads. Loads on parts are of various types: some parts are loaded with a force constantly acting in one direction, others are subject to impacts, and in others, forces more or less often change in magnitude and direction. Some parts of machines are subjected to loads at elevated temperatures, under the action of corrosion; such parts work in difficult conditions. In accordance with this, various methods for testing metals have been developed, with the help of which mechanical properties are determined. The most common tests are static tensile, dynamic and hardness tests. Static tests are those tests in which the metal being tested is subjected to a constant force or a force that increases very slowly. Dynamic tests are such tests in which the metal being tested is subjected to an impact or force that increases very quickly. In addition, in some cases, fatigue, creep and wear tests are performed, which give a more complete picture of the properties of metals. Mechanical properties are sufficient strength. Metals have a higher strength compared to other materials, so the loaded parts of machines, mechanisms and structures are usually made of metals. For the manufacture of springs and springs, special steels and alloys with high elasticity are used. The plasticity of metals makes it possible to process them by pressure (forging, rolling). physical properties. In aircraft, car and railcar construction, the weight of parts is often the most important characteristic, so aluminum and magnesium alloys are especially useful here. The specific strength for some aluminum alloys is higher than for mild steel. Fusibility is used to make castings by pouring molten metal into molds. Low-melting metals (lead) are used as a hardening medium for steel. Some complex alloys have a low melting point that melts in hot water. Such alloys are used for casting printing matrices, in devices that serve to protect against fires. Metals with high electrical conductivity are used in electrical engineering, for the construction of power lines, and alloys with high electrical resistance for incandescent electric heaters. The magnetic properties of metals play a primary role in electrical engineering (electric motors, transformers), in electrical instrumentation (telephone and telegraph sets). The thermal conductivity of metals makes it possible to produce their uniform heating for pressure treatment, heat treatment; it provides the possibility of soldering metals, their welding. Chemical properties. Corrosion resistance is especially important for products operating in highly oxidized environments (grate grates, chemical industry machine parts). To achieve high corrosion resistance, special stainless, acid-resistant and heat-resistant steels are produced, and protective coatings are also used for products. 20. Types of phases in metal alloys. Phase rule; lever rule A state diagram is a graphic representation of the state of any alloy of the system under study, depending on its concentration and temperature. The study of any alloy begins with the construction and analysis of the state diagram of the corresponding system. The state diagram makes it possible to study the phases and structural components of the alloy. Using the state diagram, it is possible to establish the possibility of heat treatment and its modes, casting temperatures, hot plastic deformation. In any system, the number of phases that are in equilibrium depends on internal and external conditions. The laws of all changes occurring in the system are subject to the general law of equilibrium, which is called the phase rule or the Gibbs law. The phase rule expresses the relationship between the number of degrees of freedom C (variance) of the system, the number of components K and the number of phases of the system Ф that are in equilibrium. Degrees of freedom are called independent thermodynamic parameters, which can be given arbitrary (in a certain interval) values so that the phase states do not change (old phases do not disappear and new ones do not appear). Usually, all transformations in metals and alloys occur at constant atmospheric pressure. Then the phase rule is written as follows: C \u1d K - F + XNUMX. The phase rule equation allows you to correct the correctness of constructing state diagrams. A phase is a homogeneous part of the system, which is separated from other parts of the system (phases) by the interface, when passing through which the chemical composition or structure of the substance changes abruptly. A homogeneous liquid is a single-phase system, and a mechanical mixture of two crystals is a two-phase system, since each crystal differs from the other in composition or structure, and they are separated from one another by an interface. Components are the substances that form the system. The construction of state diagrams is carried out by various experimental methods. Thermal analysis is often used. Several alloys of this system are selected with different mass ratios of their components. The alloys are placed in refractory crucibles and heated in a furnace. After the melting of the alloys, the crucibles with the alloys are slowly cooled and the cooling rate is fixed. Based on the data obtained, thermal curves are built in time-temperature coordinates. As a result of the measurements, a series of cooling curves are obtained, on which inflection points and temperature stops are observed at phase transformation temperatures. Temperatures corresponding to non-phase transformations are called critical points. The points corresponding to the beginning of crystallization are called liquidus points, and the points corresponding to the end of crystallization are called solidus points. Based on the obtained cooling curves for various alloys of the system under study, a phase diagram is constructed in coordinates; along the abscissa axis - concentration of components, along the ordinate axis - temperature. In the process of crystallization, both the concentration of phases and the amount of each phase change. At any point in the diagram, when two phases simultaneously exist in the alloy, the amount of both phases and their concentration can be determined. For this, the rule of leverage or the rule of segments is used. Segment rule. This diagram covers alloys whose components form mixtures of their practically pure grains with negligible mutual solubility. The abscissa shows the percentage of component B in the alloy. The phase structure of alloys in the diagram depends on temperature. With the thermodynamic action of the components on each other, the temperature of their transition to the liquid state decreases, reaching a certain minimum at a composition determined for each pair of components. The composition of the alloy can be determined by projecting point C onto the abscissa axis (point Ve). An alloy of two components that melts at a minimum temperature is called a eutectic or eutectic. The eutectic is a uniform mixture of simultaneously crystallized small grains of both components. The temperature at which both components melt or crystallize simultaneously is called the eutectic temperature. Quantitative changes in the alloys of a given system of components during crystallization obey the rule of segments. To determine the concentrations of the components in the phases, a horizontal line is drawn through a given point characterizing the state of the alloy until it intersects with the lines that limit this area; the projections of the intersection points onto the concentration axis show the compositions of the phases. By drawing a horizontal line through a given point, you can determine the quantitative ratio of the phases. The segments of this line between the given point and the points that determine the composition of the phases are inversely proportional to the quantities of these phases. The segment rule in dual state diagrams is used only in two-phase areas. In a single-phase region, there is only one phase; any point inside the region characterizes its concentration. 21. Solid solutions of substitution and insertion; intermediate phases; superstructures Solid solutions are phases in which one of the alloy components retains its crystal lattice, while the atoms of other components are located in the lattice of the first component, changing its dimensions (periods). The solid solution, which consists of two components, has one type of lattice and represents one phase. Distinguish between substitution solid solutions and interstitial solid solutions. When a substitutional solid solution is formed, the atoms of the dissolved component replace some of the atoms of the solvent in its crystal lattice. During the crystallization of a pure metal, there are two phases in the system: liquid (molten metal) and solid (grains of solidified metal). In hard alloys, phases are pure metal grains, solid solution grains, and chemical compound grains. All metals in the liquid state dissolve one into the other in any ratio. As a result of dissolution, a homogeneous liquid solution is formed with a uniform distribution of atoms of one metal among the atoms of another metal. Some metals, which vary greatly in atomic size, do not dissolve in the liquid state, and few metals dissolve in the liquid state to a limited extent. In the formation of alloys during their solidification, various interactions of the components are possible. If in the process of crystallization the force of interaction between homogeneous atoms turns out to be greater than the force of interaction between heterogeneous atoms, then after crystallization a mechanical mixture is formed, consisting of grains of pure metals. In this case, grains of one pure metal and next to them grains of another pure metal will be present in the hard alloy. This form of interaction occurs when there is a large difference in the properties of the metals included in the alloy. Another form of interaction between the substances that make up the alloy is the formation of solid solutions. Solid solutions are such solid phases in which the ratios between the components can change. In a solid solution, just as in pure metals, the atoms in space are arranged regularly, forming a crystal lattice. This is what distinguishes them from liquid solutions. In a solid solution, one of the substances that make up the alloy retains its crystal lattice, and the second substance, having lost its crystal structure, is distributed in the form of individual atoms in the crystal lattice of the first. The first substance is a solvent, and the second is soluble. Depending on the nature distributions of atoms of a soluble element distinguish between solid solutions of interstitial, substitution, and subtraction. Regardless of the type of solid solution, they have in common that they are single-phase and exist in a range of concentrations. Solid solutions are characterized by metallic bonds. In interstitial solid solutions, the atoms of the soluble element are distributed in the crystal lattice of the solvent metal, occupying places between its atoms. Earlier it was noted that in metals the atoms in the crystal lattice are located close to one another and the voids between them are small. Only atoms with very small sizes can be accommodated in such voids. Some metalloids - hydrogen, nitrogen, carbon, boron - have the smallest sizes of atoms, which form interstitial solid solutions with metals. But even for these elements, the size of atoms somewhat exceeds the size of interatomic gaps in the crystal lattice of metals, therefore, when interstitial solid solutions are formed, the lattice is distorted and stresses arise in it. In this case, the concentration of the interstitial solid solution cannot be high: it rarely exceeds 1–2%. In substitutional solid solutions, the atoms of the soluble element take the place of the atoms of the base metal. Foreign atoms can replace the atoms of the solvent in any place, so such solutions are called disordered solid solutions. The sizes of the atoms of the soluble element differ from the sizes of the solvent atom (they are larger or smaller), therefore, when a substitutional solid solution is formed, the crystal lattice of the solvent metal is slightly distorted without losing its basic structure. Substitution solid solutions can be limited and unlimited. One of the conditions for unlimited solubility is the size factor: the greater the difference in atomic radii, the smaller the solubility. With a decrease in temperature in substitutional solid solutions, a process of redistribution of atoms can occur, as a result of which the atoms of the dissolved element will occupy strictly defined places in the solvent lattice. Such solid solutions are called ordered solid solutions, and their structure is called a superstructure. The transition temperature of a disordered state into an ordered state is called the Kurnakov point. Ordered solid solutions are characterized by greater hardness, lower plasticity and electrical resistance. They can be considered as intermediate phases between solid solutions and chemical compounds. 22. System with unlimited solubility in liquid and solid states; eutectic, peritectic and monotectic systems. Systems with component polymorphism and eutectoid transformation Complete mutual solubility in the solid state is possible when both components have the same crystal lattices and the atomic diameters of the components differ little in size. Such a diagram has a simple form and consists of two liquidus and solidus lines intersecting each other at the points of crystallization of pure components A and B. All alloys solidify in a certain temperature range (C = 1). If the crystallization process proceeds under conditions of accelerated cooling, which usually takes place during the production of cast parts and ingots, then the diffusion leveling of the composition of crystals precipitated at temperatures above t3, does not have time to occur, as a result of which an unequal composition is obtained not only in individual crystals, but in each of them. The inner parts of the crystal will be richer in the refractory component B, the outer ones - in component A. This phenomenon of inhomogeneity of the chemical composition is called The first crystals on the surface of the ingot will be enriched in component B, and the last crystals formed in the middle of the ingot will be enriched in component A. As a result, macrosegregation occurs in the ingot. Segregation plays a negative role, and especially in cases where harmful impurities are unevenly distributed. The increased content of harmful impurities can lead to premature destruction of parts. Having a phase diagram, one can trace the phase transformations of any alloy and indicate the composition and quantitative ratio of the phases at any temperature. This is done with two simple rules. The chemical composition of the precipitated crystals, as the temperature decreases, changes along the solidus line from xе up to xс. At the same time, the composition of the liquid phase changes along the liquidus line from xс up to xi This gives grounds to formulate rules for determining the composition of phases (the rule of concentrations) and the quantitative ratio of phases (the rule of segments). Components: A and B; phases: W,α,β, where α is a solid solution of atoms of component B in the crystal lattice of component A, and β is a solid solution of atoms of component A in the crystal lattice of component B. Depending on the interaction of these three phases, two types of diagrams are possible: a diagram with a eutectic and a diagram with a peritectic. State diagram with eutectic. The ALL line is the liquidus line, the EVSKE line is the solidus line. The VM and CG lines show the limiting solubility of the components. As in the previous cases, the crystallization process of any alloy can be followed using the phase rule and the rule of segments. A system is a set of phases in a solid or liquid state that are in equilibrium under certain external conditions (temperature and pressure). Different allotropic forms are usually denoted by the letters of the Greek alphabet α, β, γ, which are added as indices to the symbol denoting the element. The allotropic form, which is stable at the lowest temperature, is denoted by the letter α, which exists at a higher temperature, β, then γ. An example of an allotropic transformation due to a change in pressure is the modification of the crystalline structure of carbon, which can exist in the form of graphite and diamond. Polymorphism is of great practical importance. Using this phenomenon, it is possible to strengthen or soften alloys using heat treatment. Of great practical interest are alloys in which one or both of the components have polymorphic transformations. In these alloys, as a result of heat treatment, it is possible to obtain metastable states of the structure with new properties. After crystallization of all alloys of this system in a certain temperature range, a solid solution γ is formed, which, when the temperature drops below t3 undergoes a eutectoid transformation γC → aE + b The resulting mixture of two solid phases is called a eutectoid. Due to the variable solubility of the components in solid solutions α and β, further cooling is followed by secondary precipitation of solid solutions βII and αII. Some elements modify their crystal structure, i.e., the type of crystal lattice, depending on changes in external conditions - temperature and pressure. The existence of matter in various crystalline forms, depending on external conditions, is determined by its tendency to a state with a smaller supply of free energy. This phenomenon is called polymorphism or allotropy. Each type of lattice represents an allotropic modification or modification. Each modification has its own temperature range at which it is stable. In polymorphic transformations of metals, temperature is of primary importance. The transformation of one allotropic form into another occurs at a constant temperature, called the polymorphic transformation temperature, and is accompanied by a thermal effect, similar to the phenomena of melting-solidification or evaporation-condensation. This is due to the need to spend a certain amount of energy on the rearrangement of the crystal lattice. The atomic volumes and, accordingly, the total energies of various modifications, as a rule, differ little, but there are exceptions. 23. System with triple eutectic and almost complete absence of solubility of components in the solid state; isothermal and polythermal sections State diagrams of binary alloys are built on a plane: the concentration of components is plotted along the abscissa axis, the temperature for ternary alloys is plotted along the ordinate axis. More common is the spatial image. An equilateral triangle, called the concentration triangle, is used as the base of the diagram. The temperature is plotted along an axis perpendicular to the plane of the concentration triangle. The vertices of the triangle correspond to the concentrations corresponding to the pure components A, B, and C of the system under study. On the sides of the triangle, the concentrations of the corresponding two components are plotted: A-B, B-C, C-A. Each point inside the triangle corresponds to the composition of some particular ternary alloy. The composition of the alloys is determined based on the well-known theorem in an equilateral triangle, the sum of three perpendiculars dropped from any point K, lying inside the triangle, to its sides, is equal to the height of the triangle. The height of the triangle is taken as 100%, then the perpendiculars Ka, Kc and Kb will characterize the concentrations of the individual components of the ternary alloy. The amount of each component is determined by the value of the perpendicular lowered to the opposite side, i.e. the amount of component C is determined by the perpendicular Kc, component A-Ka, component B-Kb. More often, the composition of alloys is determined not by the values of the perpendiculars, but by the values of the segments cut off on the sides of the triangle by lines parallel to the sides of the triangle, i.e., along the segments Aa, Be and CJ. The segment Ad corresponds to the concentration of the component B, the segment Be-component C. and the segment C ^ component A. The concentration is determined in the clockwise direction, but can also be determined in the opposite direction. The interaction of components in ternary alloys is similar to double ones: the formation of mechanical mixtures, solid solutions and chemical compounds is possible: eutectic and peritectic reactions, polymorphic transformations are possible. The difference is that in binary systems, transformations are indicated by lines and points, and in ternary systems, by planes and lines. For example, not a liquidus line, but a liquidus surface (or a solidus surface), not a eutectic line, but a eutectic surface. The composition of a double eutectic is determined not by a point, but by a line. And only the triple eutectic is projected on the plane of the triangle by a point. All this can be traced by studying two typical diagrams of the state of alloys of three components. Unlike double diagrams, ternary diagrams make it possible to carry out phase and structural analysis of real technical alloys, which, as a rule, are three- or more-component. The model of the ternary system is a trihedral prism resting on an equilateral triangle. The upper part of the prism is the liquidus surface. In a ternary system, where all three components are infinitely soluble in both liquid and solid states, the liquidus surface has the simplest form - it is the surface of a lentil grain cut from three sides. In all other cases, this surface turns out to be complex, consisting of several intersecting surfaces, so the study of ternary systems presents certain methodological difficulties. The base of the trihedral prism is an equilateral triangle, on which the concentrations are marked by the side faces of the state diagram of binary systems, and the height is the temperature. The choice of an equilateral triangle is explained by the fact that in it the concentrations of all components can be shown on the same scale. At the vertices of this triangle are the components A, B and C of the alloy, i.e. 100% A, 100% B and 100% C, respectively. The concentrations of binary alloys are noted on the respective sides of the triangle, and the concentrations of ternary alloys are indicated as points within the area of the triangle. There are several ways to determine the concentration of any ternary alloy. To determine the percentage of component A, it is necessary to draw from point K a line parallel to the opposite side (BC) of the triangle, until it intersects with the side - the scale of component A. To find the percentage of component B, it is necessary to draw a line from point K parallel to the opposite side (AC) , until it intersects with the side AB - the scale of component B. In a similar way, you can set the percentage of component C. It should be borne in mind that the total concentration A + B + C \u100d XNUMX%. To explain phase transformations in ternary systems, sections are used - vertical (polythermal) and horizontal (isothermal). Each horizontal section characterizes the equilibrium state at the selected temperature and can be used for quantitative calculations. The points indicating the equilibrium compositions of the phases are located on the section plane. The vertical section shows the sequence of phase transformations in alloys during heating or cooling for a certain range of component concentrations. There is no information on the equilibrium compositions of the phases on these cross sections. 24. The rule of the lever and the center of gravity of the triangle Using the phase diagram, it is possible to determine for any temperature not only the number of phases, but also their composition and quantitative ratio. To do this, apply the rule of segments (the rule of the lever). This rule can be used for diagrams in which alloys are in a two-phase state. The first rule of segments is the determination of the composition of the phases. The phase structure of alloys in the diagram depends on temperature. With the thermodynamic action of the components on each other, the temperature of their transition to the liquid state decreases, reaching a certain minimum at a composition determined for each pair of components. The composition of the alloy can be determined by projecting point C onto the x-axis (point B 3). An alloy of two components that melts at a minimum temperature is called a eutectic or eutectic. The eutectic is a uniform mixture of simultaneously crystallized small grains of both components. The temperature at which both components melt simultaneously is called the eutectic temperature. On the state diagram, the temperatures above which the alloys are in the liquid state lie on the DIA line, called the liquidus line. The transition of alloys from a liquid state to a solid state during crystallization occurs in the temperature range lying between the liquidus line and the eutectic temperature, which corresponds to the DCE solidus line. In this case, from each alloy, as the temperature decreases, at first the component, the amount of which exceeds the eutectic concentration, passes into the solid phase. In hypoeutectic alloys, the two-phase region ACD contains an excess component A and the liquid phase G, and in the hypereutectic region BSE there are respectively solid B and liquid liquid phases. In both cases, the G phase is a liquid solution of both components. As the temperature decreases and approaches it, the composition of the non-crystallized phase approaches the eutectic. In this case, the less the alloy differs in composition from the eutectic, the lower its liquidus point, and the more eutectics solidify in it. Quantitative changes in the alloys of a given system of components during crystallization obey the rule of segments. The amount of each structural component, on which the properties depend, can be calculated by the rule of segments in relation to the eutectic temperature. When evaluating the strength properties, it should be borne in mind that the part of the alloy, which is represented by the eutectic, has a higher strength than the part represented by larger grains of the excess phase. To determine the composition of the phases for an alloy at different temperatures at point n. To do this, through the point n, which characterizes the state of this alloy at temperature tn, it is necessary to draw a horizontal line (konoda) until it intersects with the lines of the state diagram that bound this two-phase region. Intersection points l2 and s2 are projected onto the concentration axis. Point projection l2 point l2 will show the composition of the liquid phase, and the points s2 - point s2 - solid phase. To determine the composition of the phases at any temperature, it is necessary to draw a conode through this point and project the points of intersection with the liquidus and solidus onto the concentration axis. The composition of the liquid phase changes along the liquidus line, and the solid phase - along the solidus line. At temperatures below the solidus line, the phase composition of all alloys of the considered system consists of grains of both components: A+B. There are small grains A and B present in any alloy, which make up the eutectic, and large grains of excess phases - components A or B, respectively, in hypoeutectic and hypereutectic alloys. Using the second position of the rule of segments, determine the quantitative ratio of the phases for any temperature. The number (mass) of phases is inversely proportional to the segments of the conducted conode. The rule of segments (lever) allows you to determine the composition and amount of solid and liquid phases of the alloy, which is in the crystallization interval. From the state diagram, one can determine not only the number of phases of a particular alloy at a given temperature, but also the relative amount of each phase. To determine the number of phases, for example, an alloy Pb - Sb containing 72% Sb, at a given temperature, it is necessary to draw a perpendicular from a point on the concentration axis corresponding to the content of 72% Sb, and a horizontal line corresponding to a given temperature tbackside. As a result of the intersection of the lines, we obtain point K. We continue the horizontal line passing through point K until it intersects with the lines of the diagram, we obtain points l and S. Point l corresponds to the liquid phase of the alloy (lies on the liquidus line), temperatures of pure antimony). Lever rule. 1. The amount of the solid phase is equal to the ratio of the length of the arm adjacent to the liquid phase to the length of the entire lever. 2. The amount of the liquid phase is equal to the ratio of the length of the arm adjacent to the solid phase to the length of the entire lever. 25. Dependence of mechanical and physical properties on the composition in systems of various types A property is a quantitative or qualitative characteristic of a material that determines its commonality or difference with other materials. There are three main groups of properties: operational, technological and cost, which underlie the choice of material, determine the technical and economic feasibility of its use. Performance properties are paramount. The performance of many parts of machines and products provides a level of mechanical properties. Mechanical properties characterize the behavior of a material under the action of an external load. Since the loading conditions of machine parts are extremely diverse, the mechanical properties include a large group of indicators. The performance of a separate group of machine parts depends not only on the mechanical properties, but also on the resistance to the action of a chemically active working environment. If such an impact becomes significant, then the physicochemical properties of the material - heat resistance and corrosion resistance - become decisive. Mechanical properties characterize the resistance of a material to deformation, destruction, or a feature of its behavior in the process of destruction. This group of properties includes indicators of strength, stiffness (elasticity), plasticity, hardness and viscosity. The main group of such indicators is the standard characteristics of mechanical properties, which are determined in laboratory conditions on samples of standard sizes. The indicators of mechanical properties obtained during such tests evaluate the behavior of materials under external load without taking into account the design of the part and their operating conditions. In addition, the structural strength indicators are additionally determined, which are in the greatest correlation with the service properties of a particular product and evaluate the performance of the material under operating conditions. The mechanical properties of materials characterize the possibility of their use in products operated under the influence of mechanical loads. The main indicators of such properties are strength parameters, hardness and tribological characteristics. They are not "pure" constants of materials, but they significantly depend on the shape, dimensions, and state of the surface of the samples, as well as test modes, primarily the loading rate, temperature, exposure to media, and other factors. The high hardness of the metal is important in the manufacture of cutting products. Most often, tool steels are used for such products. Strength - the property of materials to resist destruction, as well as irreversible change in shape under the influence of external loads. It is due to the forces of interaction of atomic particles that make up the material. The strength of the interaction of two neighboring atoms depends on the distance between them, if we neglect the influence of the surrounding atoms. Deformation is a change in the relative arrangement of particles in a material. Its simplest types are: tension, compression, bending, torsion, shear. Deformation - a change in the shape and size of the sample or its parts as a result of deformation. The limit of proportionality is the stress at which the deviation from the linear relationship between stresses and strains reaches a certain value established by the specifications. Important physical properties of materials that are taken into account when using materials are density, heat capacity, thermal conductivity, thermal expansion, and electrical conductivity. The special magnetic properties of iron, nickel, cobalt and their alloys, as well as ferrites, singled them out into a group of materials of exceptional value - ferro- and ferrimagnets. Physical properties are determined by the type of interatomic bond and the chemical composition of materials, temperature and pressure. For most material processing processes, pressures do not exceed 500 MPa. Such pressures practically do not affect the values of physical properties. There are physical properties dependent and independent of the structure of the material. The values of the latter are determined only by the chemical composition of the material and temperature. Physical properties of metals - color, density, melting point, thermal and electrical conductivity, ability to be magnetized, etc. Copper, for example, is a red metal, and pink in a fracture; silver-white aluminum; lead is light grey. An important characteristic of physical properties is electrical conductivity. Copper has the highest electrical conductivity after silver. Aluminum has a low density, so parts made of aluminum and alloys based on it are widely used in automobiles and tractor construction. Copper and aluminum, which have high electrical conductivity, are used to make conductors (transformer windings, power lines). The weight of the product or part also plays an important role and acts as the main characteristic. 26. Selection of alloys for a specific purpose based on the analysis of state diagrams Pure metals are used in electrical and radio engineering (conductor, electrovacuum). Main structural materials are metal alloys. An alloy is a substance obtained by fusing two or more elements (components). An alloy made primarily from metallic elements and having metallic properties is called a metal alloy. Pseudo-alloys - alloys created by sintering, sublimation, electrolysis. Metal alloys can be obtained by powder metallurgy, diffusion and other methods. The predominant use of metal alloys in technology is explained by the fact that they have more valuable complexes of mechanical, physical and technological properties than pure metals. The main concepts in the theory of alloys are: system, component, phase, variance. System - a group of bodies allocated for observation and study. In metal science, systems are metals and metal alloys. Pure metal is a simple system. Alloys consist of two or more components and are complex systems. Components are called substances that form a system, taken in a smaller number. In metal alloys, the components can be elements (metals and non-metals) and chemical compounds. A phase is a homogeneous part of the system, separated from another part of the system (phase) by an interface, when passing through which the chemical composition or structure changes abruptly. For example, during the crystallization of a pure metal, there are two phases in the system: liquid (molten metal) and solid (grains of solidified metal). In hard alloys, phases can be pure metal grains, solid solution grains, and chemical compound grains. Variance - the number of internal and external factors that can be changed with a constant number of phases in the system. All metals in the liquid state dissolve one into the other in any ratio. As a result of dissolution, a homogeneous liquid solution is formed with a uniform distribution of atoms of one metal among the atoms of another metal. Due to this interaction, in practice, in order to uniformly distribute the substances in the alloy, as a rule, they resort to their melting. Only a very few metals, mainly those with very different sizes of atoms, do not dissolve in the liquid state. Also, few metals dissolve in the liquid state to a limited extent. In the formation of alloys during their solidification, various interactions of the components are possible. If in the process of crystallization the force of interaction between homogeneous atoms turns out to be greater than the force of interaction between heterogeneous atoms, then after crystallization a mechanical mixture is formed, consisting of grains of pure metals. In this case, grains of one pure metal and next to them grains of another pure metal will be present in the hard alloy. This form of interaction occurs when there is a large difference in the properties of the metals included in the alloy. Another form of interaction between the substances that make up the alloy is the formation of solid solutions. Solid solutions are such solid phases in which the ratios between the components can change. In a solid solution, as well as in pure metals, the atoms in space are arranged regularly, forming a crystal lattice. This is what distinguishes them from liquid solutions. In a solid solution, one of the substances that make up the alloy retains its crystal lattice, and the second substance, having lost its crystal structure, is distributed in the form of individual atoms in the crystal lattice of the first. The first substance is a solvent, and the second is soluble. Depending on the nature of the distribution of atoms of a soluble element, solid solutions of interstitial, substitution, and subtraction are distinguished. Solid solutions are also divided depending on the degree of solubility of the components into solutions with limited solubility of the components and with unlimited solubility. The construction of state diagrams is carried out by various experimental methods. The most commonly used method is thermal analysis. The experimental essence of this method is as follows. Several alloys of this system are selected with different mass ratios of their components. There are alloys - mechanical mixtures that are formed when it is impossible to dissolve the components that are in the solid state. These components cannot form compounds through a chemical reaction. Mechanical mixtures include elements with different properties and structure. The composition of the alloy includes crystals of components that form crystal lattices. Chemical compounds are alloys that are formed from different elements containing dissimilar atoms, between which the interaction force is much higher than between homogeneous atoms. 27. Structure and properties of iron; metastable and stable iron-carbon phase diagrams. Formation of the structure of carbon steels. Determination of carbon content in steel by structure Alloys of iron and carbon are the most common metal materials. The iron-carbon state diagram gives an idea of the structure of iron-carbon alloys - steels and cast irons. Pure iron is a silvery-light metal, practically unaffected by oxidation. Atomic number 26, atomic weight 55,85. Technically pure iron contains 0,10-0,15% of all impurities. The properties of iron depend on its degree of purity. Melting point - 1539 ° C, density - 7,85 g / cm3. Iron has low hardness and strength and good ductility. Pure iron is less durable than cast iron or steel. Iron forms solutions with many elements: with metals - substitution solutions, with carbon, nitrogen and hydrogen - interstitial solutions. The solubility of carbon in iron depends on the crystalline form of the iron. When carbon is dissolved in iron, solid solutions are formed. Ferrite is a solution obtained by dissolving carbon in a low-temperature modification of iron. It is characterized by low hardness and high ductility. Carbon, dissolving in the high-temperature modification of iron, forms plastic austenite. Carbon occurs in nature in the form of two modifications: in the form of diamond, which has a complex cubic lattice, and in the form of graphite, which has a simple hexagonal lattice. Cementite is iron carbide containing 6,67% carbon. Brittle and hard. In the event that a large amount of silicon is present in the metal, the formation of cementite does not occur. In this case, carbon is converted into graphite (grey cast iron). The carbon content in the diagram Fe - C (cementite) is limited to 6,67%, since at this concentration a chemical compound is formed - iron carbide (FeзC) or cementite, which is the second component of this diagram. Re - Fe system3C is metastable. The formation of cementite instead of graphite gives a smaller gain in free energy, but the kinetic formation of iron carbide is more likely. Point A (1539 °C) corresponds to the melting point of iron, point D (1500 °C) to the melting point of cementite, points N (1392 °C) and G (910 °C) correspond to the polymorphic transformation. Iron-carbon alloys are steels and cast irons, which are the main materials used in mechanical engineering and modern technology. Steel is the main metal material widely used for the manufacture of machine parts, aircraft, instruments, various tools and building structures. The widespread use of steels is due to a complex of mechanical, physicochemical and technological properties. Steels combine high rigidity with static and cyclic strength. These parameters are changed by changing the concentration of carbon, alloying elements and technologies of thermal and chemical-thermal treatment. By changing the chemical composition, steels with different properties are obtained and used in many branches of technology and the national economy. Carbon steels are classified according to carbon content, purpose, quality, degree of deoxidation and structure in an equilibrium state. According to the carbon content, steels are divided into low-carbon (< 0,3% C), medium-carbon (0,3-0,7% C) and high-carbon (> 0,7% C). According to their purpose, steels are classified into structural and tool steels. Structural steels represent the most extensive group, which is intended for the manufacture of building structures, machine parts and devices. These steels include cemented, improved, high-strength and spring-loaded steels. Tool steels are divided into steels for cutting, measuring tools, dies of cold and hot (up to 200 ° C) deformation. Steels are classified by quality into ordinary quality, high-quality, high-quality. The quality of steel is a set of properties determined by the metallurgical process of its production. The uniformity of the chemical composition, structure and properties of steel, as well as its manufacturability, largely depend on the content of gases (oxygen, hydrogen, nitrogen) and harmful impurities - sulfur and phosphorus. Gases are latent, quantitatively difficult to determine impurities, therefore, the norms for the content of harmful impurities serve as the main indicators for separating steels by quality. Steels of ordinary quality are only carbon (up to 0,5% C), high-quality and high-quality - carbon and alloyed. According to the degree of deoxidation and the nature of solidification, steels are classified into calm, semi-calm and boiling. Alloy steels are produced calm, carbon steels - calm, semi-quiet and boiling. According to the structure in the equilibrium state, steels are divided into: 1) hypoeutectoid, having ferrite and pearlite in the structure; 2) eutectoid, the structure of which consists of perlite; 3) hypereutectoid, having pearlite and secondary cementite in the structure. 28. Structural and tool carbon steels. Marking, application Carbon structural steels are divided into ordinary quality steels and high quality steels. Steel grades of ordinary quality St0, St1, St2, ..., St6 (as the number increases, the carbon content increases). Steels of ordinary quality, especially boiling ones, are the cheapest. From steels of ordinary quality, hot-rolled ordinary steel is produced: beams, bars, sheets, pipes. Steels are used in construction for welded and bolted structures. As the carbon content in the steel increases, the weldability deteriorates. Steels St5 and St6, which have a higher carbon content, are used for elements of building structures that are not subjected to welding. The smelting of high-quality carbon steel is carried out under strict conditions regarding the composition of the charge and the conduct of melting and casting. High-quality carbon steels are marked with the numbers 08, 10, 15, ..., 85, indicating the average carbon content in hundredths of a percent. Low carbon steels have high strength and high ductility. Steels not thermally treated are used for lightly loaded parts, critical welded structures, for machine parts hardened by carburizing. Medium carbon steels (0.3-0.5% C) 30, 35, ..., 55 are used after normalization, improvement and surface hardening. These steels have high strength with lower ductility, they are used for the manufacture of small or large parts that do not require through hardenability. Steels with a high carbon content have high strength and wear resistance. Springs and springs, lock washers, rolling rolls are made from these steels. Structural strength is a complex of mechanical properties that ensures long-term and reliable operation of the material under its operating conditions. Structural strength is the strength of the material of construction, taking into account structural, metallurgical, technological and operational factors. Four criteria are taken into account: the strength of the material, the reliability and durability of the material under the conditions of operation of this structure. Strength - the ability of a body to resist deformation and destruction. Reliability - the property of the product to perform the specified functions and maintain its performance for the required period of time. The reliability of a design is its ability to work outside the design situation. The main indicator of reliability is the viscosity margin of the material, which depends on the composition, temperature, loading conditions, work absorbed during crack propagation. The resistance of a material to brittle fracture is the most important characteristic that determines the reliability of structures. Durability - the property of the product to maintain performance to the limit state (the impossibility of its further operation). Durability depends on the conditions of its operation (these are wear resistance during friction and contact strength, material resistance to surface wear that occurs during rolling friction with sliding). Tool steels are intended for the manufacture of cutting, measuring tools and dies of cold and hot deformation. The main properties for the tool are wear resistance and heat resistance. A high surface hardness is required for wear resistance of the tool, and the steel must be strong, hard and tough to retain the shape of the tool. The possible heating temperature of the cutting tool depends on the heat resistance of steel. Carbon tool steels are the cheapest. They are mainly used for the manufacture of low-responsibility cutting tools and for die-tool equipment of a regulated size. High-quality (U1435, U74, U7) and high-quality (U8A, U9A, U7A) carbon steels are produced (GOST 8-9). The letter U in the brand shows that the steel is carbon, and the figure shows the average carbon content in tenths of a percent. The letter A at the end of the brand shows that the steel is high quality. Carbon steels are delivered after annealing to granular perlite. Due to the low hardness in the delivered condition (HB 187-217), carbon steels are well machined and deformed, which makes it possible to use knurling, notching and other high-performance tool manufacturing methods. Steel grades U7, U8, U9 are subjected to complete hardening and tempering at 275-350 ° C for reed; since they are more viscous, they are used for the production of woodworking, plumbing, blacksmithing and pressing tools. Hypereutectoid steel grades U10, U11, U12 are subjected to incomplete hardening. The tool of these brands has increased wear resistance and high hardness. Hypereutectoid steels are used for the manufacture of measuring tools (gauges), cutting tools (files, drills) and cold heading and drawing dies operating at low loads. The disadvantage of tool carbon steels is the loss of strength when heated above 200 ° C (lack of heat resistance). Tools made of these steels are used for machining soft materials and at low cutting or deformation speeds. 29. White, gray, half, ductile and malleable cast irons Microstructure formation, properties, labeling and applications Cast iron is an alloy of iron and carbon. Cast iron contains carbon - 2,14% and is a cheaper material than steel. It has a low melting point and good casting properties. It is possible to make castings of more complex shapes from cast irons than from steels. The cast structure of cast iron contains stress concentrators, which can be defects: porosity, segregation heterogeneity, microcracks. White cast iron is named after the matte white fracture. All carbon in this cast iron is in the bound state in the form of cementite. Phase transformations proceed according to the state diagram (Fe - FeзWITH). White cast irons, depending on the carbon content, are: hypoeutectic (perlite + ledeburite); eutectic (ledeburite); hypereutectic (primary cementite + ledeburite). These cast irons have greater hardness due to the cementite content; they are very fragile and are not used for the manufacture of machine parts. White cast iron castings are used to produce ductile iron parts by graphitizing annealing. Chilled casting irons have surface layers (12-30 mm) with a white cast iron structure, and a gray cast iron core. The high hardness of the surface allows it to work well against abrasion. These properties of chilled iron are used to make sheet mill rolls, wheels, mill balls, brake shoes, and other parts. White cast irons crystallize according to the state diagram of the iron-cementite alloy system. A significant content of hard and brittle cementite in the composition of white cast irons is the reason that these cast irons are difficult to machine. They are used for casting parts with subsequent annealing for ductile iron, as well as for casting rolling rolls and wagon wheels. Gray cast iron (technical) got its name from the type of fracture, which has a gray color. Graphite is present in the structure of gray cast iron. The structure of cast iron consists of a metal base and graphite, and its properties depend on these two components. Graphite has low mechanical properties. With slow cooling of iron-carbon alloys, graphite is released. In industry, hypoeutectic gray (foundry) cast irons are used. Gray cast iron, which consists of ferrite and graphite, is called ferritic, since its metal base is ferrite. All carbon in the form of graphite is released during very slow cooling of the alloy; if the cooling rate during crystallization (both primary and secondary) increases, not graphite is released, but cementite. Cast iron, containing up to 1,2% phosphorus, is used for artistic casting, pipes. Gray cast iron marking. According to GOST, cast iron in castings is marked with the letters SCh with the addition of two numbers: the first number indicates the tensile strength (σpch) the second is elongation (σ) in%. Half cast iron is composed of pearlite, ledeburite and lamellar graphite. Combines two colors - gray and white. Ductile iron is cast iron in which the graphite is spheroidal. An increase in the strength and ductility of cast iron is achieved by modification, which ensures the production of globular (spheroidal) graphite instead of lamellar. The spheroidal graphite surface has a smaller relation to volume and determines the greatest continuity of the metal base and the strength of cast iron. This form of graphite is obtained by adding magnesium (M) or cerium (Ce) to liquid cast iron. Ductile iron has a ferritic or pearlitic base. Ferritic cast iron has increased ductility. According to GOST, cast iron is designated by numbers: the first number indicates the tensile strength (σpch), the second is elongation (σ) in%. Even higher strength is achieved by modifying alloyed cast iron. Ductile iron is used instead of steel for the manufacture of machine parts, forging and pressing equipment operating in bearings at elevated and high pressures; crankshafts, gears, couplings and instead of ductile iron for the manufacture of rear axles-cars. Ductile cast iron - graphite flake cast iron, the code name for soft and ductile cast iron, which is obtained from white cast iron by special heat treatment; it is not subjected to forging, it has high ductility. Ductile iron consists of a steel base and contains carbon in the form of graphite. Graphite is in the form of inclusions of a rounded shape, located isolated from each other and the metal base is less separated, and the alloy has a significant toughness and ductility. The properties of ductile iron depend on the size of graphite inclusions (the smaller these inclusions, the stronger the cast iron), but they are determined by the structure of its metal base, which can be ferritic, pearlitic or mixed. Depending on the composition of the cast iron and the method of heat treatment, two types of ductile iron are obtained: black-hearted and white-hearted. Malleable cast iron is a cheaper material, it has good mechanical properties and is used in agricultural engineering, in the automotive industry, car building, and machine tool building. 30. The role of heat treatment in improving the quality of structural materials The main prerequisites for obtaining the necessary set of mechanical and other properties for structural alloys are laid during their development and smelting. The implementation of the required properties is carried out at subsequent stages of processing, with the aim of giving the alloy not only the shape and dimensions provided for by the drawing, but also a rational internal structure, which should be understood as the structural-phase composition and dislocation structure, on which the complex of required properties directly depends. The most important stages of alloy processing are heat treatment and surface hardening. Heat treatment provides a given level of properties throughout the entire volume of the part, and surface hardening - only in certain most loaded and heavily worn areas on the surface of the part. The basic rules for heat treatment were developed by D.K. Chernov and supplemented by A.A. Bochvarov, G.V. Kurdyumov, A.P. Gulyaev. Heat treatment is understood as a complex of operations of heating and cooling an alloy, carried out according to a certain regime in order to change its structure and obtain desired properties. The basis of heat treatment is the change in the structural-phase composition and dislocation structure of the alloy, which can be achieved by using such key factors as the presence of allotropic transformations in it or the limited mutual solubility of the components depending on the temperature. All existing types of heat treatment aimed at significantly changing the phase and dislocation structure of alloys and obtaining an optimal set of operational properties are based on the use of one of the above factors. In their absence, only very limited results can be obtained by heat treatment. The two most common types of heat treatment. One of them is based on the use of the specifics of transformations in alloys due to the presence of allotropic transformations in them, and the other is based on the variable solubility of the components in each other during heating and cooling. In both cases, the fundamental basis of the heat treatment technology, which guarantees the expected results, is its mode. It includes the following elements: heating temperature, heating rate to a given temperature, holding time at this temperature and cooling rate. Heat treatment can be preliminary and final. Preliminary heat treatment is used in cases where the material needs to be prepared for further technological influences - pressure, cutting, etc. Final heat treatment is used to prepare the properties of the finished material. The specific values that characterize each of the elements of the heat treatment mode depend on the chemical composition of the alloy being processed, the size of the part, and the purpose of the type of heat treatment being performed. By varying these values, one can significantly change the phase and dislocation structures of the alloy and impart desired properties to it. The nature of the transformations occurring in the alloy and the very possibility of obtaining the required structure after heat treatment depend on the heating temperature. It is selected depending on the chemical composition of the alloy and the purpose of the heat treatment. The heating rate is chosen in such a way as to ensure minimal heating time losses, and at the same time, its value should exclude the occurrence of dangerous thermal stresses in the workpiece that can lead to warping and cracking of the part, which is observed when heating is too fast. The heating rate depends on the thermal conductivity of the processed alloy, which, in turn, is determined by its chemical composition. With the complication of the composition, thermal conductivity deteriorates. Therefore, the heating of alloys that are unfavorable in composition to certain temperatures is carried out very slowly, and then accelerated. The holding time of the part upon reaching the specified temperature should be sufficient for its heating from the surface to the core in the largest section, as well as for the complete completion in the alloy of those structural-phase transformations that have a diffusion nature, which should occur in it at a given temperature. The cooling rate during heat treatment is a very important element of the regime, on which the features of the phase and dislocation structure acquired by the alloy depend. It should be sufficient for the necessary transformations to occur in the alloy, but not too large in order to avoid dangerous thermal and phase stresses that can cause cracking or deformation (warping) of the part. Heat treatment is used to improve structural materials, in particular steel. The time of heat treatment directly depends on the size of the processed materials and parts. 31. The use of heat treatment in the technology of production of blanks and products from structural materials The most characteristic and well-studied process is the heat treatment of steel. This process is based on the presence of allotropic transformations in it, which occur during heating and cooling in the region of certain critical temperatures. Controlled structural-phase processes in steel, which provide the required phase and dislocation structure, occur due to the presence of allotropy. Structural strength is a certain set of mechanical properties that ensures long-term and reliable operation of the material under its operating conditions. Structural strength is the strength of the structural material, taking into account structural, metallurgical, technological and operational factors, i.e. this is a complex concept. It is believed that at least four criteria must be taken into account: the rigidity of the structure, the strength of the material, the reliability and durability of the material under the conditions of operation of this structure. Structural rigidity. For many power structural elements - frames, stringers, flat plates, cylindrical shells, etc. - the condition that determines their performance is local or general stiffness (stability), determined by their structural shape, stress state scheme, etc., as well as material properties. An indicator of the stiffness of a material is the modulus of longitudinal elasticity E (stiffness modulus) - a structurally insensitive characteristic that depends only on the nature of the material. Among the main structural materials, steel has the highest value of the E modulus, while magnesium alloys and fiberglass have the lowest value. However, the assessment of these materials changes significantly when taking into account their density and using the criteria of specific stiffness and stability. When evaluated according to these criteria, selected according to the shape and stress state, in many cases the most favorable material is magnesium alloys and glass-reinforced plastics, the least advantageous are carbon and alloy steels. Strength - the ability of a body to resist deformation and destruction. Most strength specifications are determined by static tensile testing. These characteristics depend on the structure and heat treatment. When evaluating the actual strength of a structural material, one should take into account the characteristics of plasticity, the viscosity of the material, since these indicators mainly determine the possibility of brittle fracture. This also applies to high-strength materials, which, having high strength, are prone to brittle fracture. Reliability - the property of the product to perform the specified functions, while maintaining its performance within the specified limits for the required period of time or the required operating time. The reliability of a structure is also its ability to work outside the design situation, for example, to withstand shock loads. The main indicator of reliability is the viscosity margin of the material, which depends on the composition, temperature (cold brittleness threshold), loading conditions, work absorbed during crack propagation. The resistance of a material to brittle fracture is the most important characteristic that determines the reliability of structures. Durability - the property of the product to maintain performance to the limit state (the impossibility of its further operation). The durability of the structure depends on the conditions of its work. First of all, these are wear resistance during friction and contact strength (resistance of the material to surface wear that occurs during rolling friction with sliding). In addition, the durability of the product depends on the endurance limit, which in turn depends on the state of the surface and the corrosion resistance of the material. During the heat treatment of materials, special equipment is used: electric furnaces, gas-flame and elevator furnaces, hardening tanks, salt baths, etc. The main types of heat treatment: volumetric, surface, local hardening; normalized, homogenizing, recrystallization annealing, chemical-thermal treatment and laser heating treatment; hardening by electric pulse field; heat treatment when applying plastic deformation, as well as cold treatment. Structural steels are steels that are used in the production of various machine parts and any structures. Those steels that are used in the construction of structures or structures are called building steels. Structural steels include both alloyed and carbon steels. In mechanical engineering, structural alloy steels GOST 4543-71 are widely used, which are: chromium, manganese, chromium-silicon, chromium-silicon-manganese, chromium-nickel, etc. Depending on the technical characteristics, these steels are divided into carburizing steels, steels for nitriding, improved steels through heat treatment, air-hardened steels, etc. 32. Annealing of the 1st kind. Non-equilibrium crystallization This type of heat treatment is possible for any metals and alloys. Its implementation is not due to phase transformations in the solid state. Heating during annealing of the 1st kind, increasing the mobility of atoms, partially or completely eliminates chemical inhomogeneity, reduces internal stresses, i.e., contributes to obtaining a more equilibrium state. During such annealing, the heating temperature and the holding time at this temperature are of primary importance, since it is these parameters that determine the rate of processes that eliminate deviations from the equilibrium state. The rate of heating and cooling for annealing of the 1st kind is of secondary importance. There are the following types of annealing of the 1st kind: diffusion annealing (homogenizing) is used to eliminate the chemical heterogeneity that occurs during the crystallization of the alloy (dendritic segregation). Alignment of the chemical composition occurs due to diffusion processes, the rate of which depends on temperature. Recrystallization annealing is used after cold plastic deformation (cold working by pressure) to remove work hardening and obtain an equilibrium state of the alloy. As a result of recrystallization, new grains are formed in the deformed metal, stresses are relieved, and the plasticity of the metal is restored. Annealing to relieve stresses that occur during forging, welding, casting, which can cause warping, i.e., a change in shape, size, and even destruction of products. non-equilibrium crystallization. The diffusion process proceeds slowly, therefore, under real cooling conditions, the composition within each crystal and different crystals does not have time to equalize and will not be the same. If the decomposition of a solid solution is possible during cooling, then the state diagram shows the beginning of this process at the slowest cooling. With an increase in the cooling rate, the temperature at which precipitation of the excess phase begins decreases, the amount of the precipitated phase decreases, and when a higher cooling rate is determined, the solid solution without precipitation is completely supercooled to room temperature. By adjusting the cooling rate, it is possible to achieve varying degrees of decomposition up to its complete suppression. Such supersaturated solutions are unstable. If the thermal mobility of the atoms of the supercooled solution is insufficient, then the state of supersaturation can persist indefinitely. Otherwise, over time, a gradual decomposition of the supersaturated solution will occur with the release of an excess phase. This process will accelerate as the temperature rises. Secondary phases, which are formed at high temperature, during slow cooling of the solid solution or high secondary heating of the quenched (supersaturated) solid solution, are not only larger in size, but are orientationally unrelated to the mother phase. The layer of atoms belonging to the old phase borders on the layer of atoms that belong to the lattice of the new phase. For the case of precipitation at low temperature, the new β-phase is oriented in a certain way with respect to the initial one, so that the boundary layer of atoms equally belongs to both lattices. Such an articulation of crystal lattices is called coherent. At the interface with coherent coupling, stresses arise and remain the greater, the greater the difference in the structure (in the interface plane) of the conjugate lattices. If the temperature of the alloy is increased, then due to an increase in the thermal mobility of atoms and the presence of stresses at the phase boundaries, the coherent bond breaks (the phenomenon of coherence breakdown), the metastable phases pass into a stable β-phase, lamellar crystals of the β-phase grow, tending to take a rounded shape. When these processes are complete, the structure and phase composition will be the same as in the case of slow cooling. The process of fixing the unstable state by rapid cooling is called quenching, and the subsequent process of gradually approaching the equilibrium state (by heating or long exposure) is called tempering and aging. Such a diverse change in the structure, achieved by varying degrees of approximation of the alloy to the equilibrium state, leads to a diverse change in properties, which is the reason for the widespread use of heat treatment, which is based on the processes of nonequilibrium crystallization. Alloys are substances composed of two or more elements from the periodic table. They are obtained by sintering or fusion. A component is a substance that forms an alloy. A phase is a spatially limited and distinct part of a system that has its own crystal lattice and its own properties. Homogeneous substances have one phase, while heterogeneous substances have several phases. Structure - the structure of the metal, in which it is possible to distinguish between individual phases, their shape, size and relative position. Structure affects properties. The equilibrium state is when in the alloy all the phases inherent in this system are formed. This state is ensured by slow cooling; it is possible to distinguish the sizes and shapes of the phases. Non-equilibrium state - the process of formation and separation of phases has not ended, it is formed during rapid cooling. 33. Homogenization annealing, change in structure and properties during homogenization annealing. Hardening with polymorphic transformation. Hardening without polymorphic transformation Annealing - operations of heating and slow cooling of steel in order to equalize the chemical composition, obtain an equilibrium structure, relieve stress. Annealing is used to obtain an equilibrium structure, therefore, during annealing, the parts are cooled slowly. Carbon steels - at a rate of 200 °C / h, alloy steels - 30-100 °C / h. Diffusion (homogenizing) annealing is used to eliminate segregation (leveling of the chemical composition). It is based on diffusion. In this case, the composition is leveled and excess carbides are dissolved. Such annealing is carried out at a high temperature with a long exposure. Homogenizing annealing is applied to alloyed steels. This is explained by the fact that the diffusion rate of carbon dissolved in austenite by the interstitial method is several orders of magnitude higher than the diffusion rate of alloying elements that are dissolved in austenite by the substitution method. Homogenization of carbon steels occurs practically in the process of their heating. Homogenizing annealing mode: heating to a temperature of 1050-1200 °C, holding time is 8-10 hours. The homogenization temperature should be high enough, but overburning and melting of the grains should not be allowed. When burnt, air oxygen combines with metal particles, oxide shells are formed that separate the grains. Overheating in the metal cannot be eliminated. Burnt metal is the final marriage. Diffusion annealing usually results in coarse grains, which should be corrected by subsequent full annealing. Complete annealing is associated with phase recrystallization and grain refinement. Steel in the equilibrium state contains perlite and is the most ductile. The purpose of full annealing is to improve the structure of steel to facilitate subsequent processing by cutting, stamping or hardening, obtaining a fine-grained equilibrium structure in the finished part. Types (methods) of complete annealing: annealing (normal and isothermal) on lamellar pearlite (cementite inclusions in the form of plates) and annealing on granular pearlite (cementite inclusions in the form of grains). When annealing on lamellar perlite, the blanks are cooled together with the furnace, most often with partial fuel supply, so that the cooling rate is in the range of 10-20 ° C per hour. Annealing achieves grain refinement. A coarse-grained structure is obtained during the hardening of steel due to the free growth of grains, as a result of steel overheating; such a structure causes a decrease in the mechanical properties of the parts. Hardening with polymorphic transformation. Hardening without polymorphic transformation Hardening is a heat treatment in which the steel acquires a non-equilibrium structure, which is primarily expressed in an increase in the hardness of the steel. Hardening includes: heat treatment for sorbitol, trostite and martensite. The degree of non-equilibrium of hardening products increases with increasing cooling rate and increases from sorbite to martensite. The advantage of true hardening is the possibility of obtaining products from martensite due to the subsequent tempering of products with sets of properties that cannot be obtained by other types of heat treatment. True hardening has been widely used as a pretreatment before tempering. The critical quenching rate is important. The hardenability of steel depends on it, i.e., the ability to be hardened to a certain depth. The critical hardening rate depends on the stability of austenite, which is determined by the amount of carbon and alloying elements dissolved in it. The introduction of carbon and alloying elements into the steel increases the hardenability, which is evaluated using cylindrical samples according to the depth of the semi-martensite layer in them. The semi-martensitic layer of steel contains 50% M and 50% T. The main parameters for hardening are heating temperature and cooling rate. The heating temperature for steels is determined from state diagrams, the cooling rate is determined from diagrams of the isothermal decomposition of austenite. The heating time depends on the size of the part and the thermal conductivity of the steel, determined experimentally. One of the goals of alloying structural steels is to reduce the critical quenching rate and obtain through-hardenability of parts made from them during quenching not only in water, but also in softer cooling media. The level of thermal and phase stresses and the probability of formation of cracks in the part depend on the sharpness of the cooling medium. In connection with the above, when quenching, soft quenching media are preferred. When hardening a cutting tool made of high-carbon steel, in order to reduce internal stresses, cooling in two environments is used. For high-carbon steels, and especially for steels with a sufficiently high content of alloying elements, the M point lies below room temperature, and often below 0 °C. In this regard, during conventional hardening, a lot of residual austenite is retained in them. Its presence reduces the hardness of the hardened steel and its thermal conductivity, which is especially undesirable for a cutting tool. Over time, residual austenite undergoes phase transformations, leading to a change in the dimensions of the product. This is extremely unacceptable for a measuring tool (staples, plugs). 34. Changes in the microstructure and mechanical properties of metals during heating after hot and cold working by pressure Processing of metals by pressure is based on their ability under certain conditions to plastically deform as a result of external forces acting on a deformable body (workpiece). If during elastic deformations the deformable body completely restores its original shape and dimensions after the removal of external forces, then during plastic deformations the change in shape and dimensions caused by the action of external forces persists after the termination of these forces. Elastic deformation is characterized by the displacement of atoms relative to each other by an amount less than the interatomic distances, and after the removal of external forces, the atoms return to their original position. Under plastic deformations, the atoms are displaced relative to each other by values greater than the interatomic distances, and after the removal of external forces, they do not return to their original position, but occupy new equilibrium positions. Depending on the temperature and speed conditions of deformation, cold and hot deformation are distinguished. Cold deformation is characterized by a change in the shape of the grains, which are elongated in the direction of the most intense metal flow. During cold deformation, the shape change is accompanied by a change in the mechanical and physicochemical properties of the metal. This phenomenon is called hardening (hardening). The change in mechanical properties is that during cold plastic deformation, as it increases, the strength characteristics increase, while the plasticity characteristics decrease. The metal becomes harder, but less ductile. Hardening occurs due to the rotation of the slip planes, an increase in the distortion of the crystal lattice in the process of cold deformation (accumulation of dislocations at the grain boundaries). The changes introduced by cold deformation into the structure and properties of the metal are not irreversible. They can be eliminated, for example, by heat treatment (annealing). In this case, an internal rearrangement occurs, in which, due to additional thermal energy, which increases the mobility of atoms, new grains grow from many centers in the solid metal without phase transformations, replacing elongated, deformed grains. Since in a uniform temperature field the grain growth rate is the same in all directions, new grains that appear instead of deformed ones have approximately the same size in all directions. The phenomenon of nucleation and growth of new equiaxed grains instead of deformed, elongated ones, occurring at certain temperatures, is called recrystallization. For pure metals, recrystallization begins at an absolute temperature equal to 0,4 of the absolute melting point of the metal. Recrystallization proceeds at a certain rate, and the time required for recrystallization is the smaller, the higher the heating temperature of the deformed workpiece. At temperatures below the recrystallization start temperature, a phenomenon called rebound occurs. When returning (resting), the shape and size of the deformed, elongated grains do not change, but the residual stresses are partially removed. These stresses arise due to non-uniform heating or cooling (during casting and pressure treatment), non-uniform distribution of deformations during plastic deformation. Residual stresses create systems of mutually balanced forces and are located in the workpiece, not loaded by external forces. The removal of residual stresses during the return almost does not change the mechanical properties of the metal, but affects some of its physical and chemical properties. Hot deformation is a deformation characterized by the ratio of the rates of deformation and recrystallization, at which recrystallization has time to occur throughout the entire volume of the workpiece and the microstructure after pressure treatment turns out to be equiaxed, without traces of hardening. To ensure the conditions for hot deformation, it is necessary to increase the heating temperature of the workpiece with an increase in its rate (to increase the rate of recrystallization). If the metal at the end of the deformation has a structure that is not completely recrystallized, with traces of hardening, then such deformation is called incomplete hot deformation. Incomplete hot deformation leads to a heterogeneous structure, a decrease in mechanical properties and plasticity. In hot deformation, the resistance to deformation is about 10 times less than in cold deformation, and the absence of hardening leads to the fact that the resistance to deformation (yield strength) changes slightly during the forming process. This circumstance explains mainly the fact that hot working is used for the manufacture of large parts, since it requires less deformation forces (less powerful equipment). During hot deformation, the plasticity of the metal is higher than during cold deformation. The influence of cold deformation on metal properties can be used to obtain the best performance properties of parts, and the control of the change in properties in the required direction and by the desired value can be achieved by choosing a rational combination of cold and hot deformation, as well as the number and modes of heat treatments in the process of manufacturing the part. 35. Return, primary and collective recrystallization. Recrystallization annealing About 10-15% of all energy expended on plastic deformation is absorbed by the metal and accumulates in it in the form of increased potential energy of displaced atoms, stresses. The deformed metal is in a non-equilibrium, unstable state. The transition to a more equilibrium state is associated with a decrease in distortions in the crystal lattice, the removal of stresses, which is determined by the possibility of moving atoms. At low temperatures, the mobility of the atom is small, and in the state of cold hardening it can persist indefinitely. With an increase in temperature, the diffusion of atoms increases and processes begin to develop in the metal, leading it to a more equilibrium state. This is the return phenomenon. The first stage of return - rest, is observed with low heating. During rest, there is a decrease in the number of vacancies, a decrease in the density of dislocations, and a partial release of stresses. The second stage of return is polygonization, the division of grains into parts - polygons (subgrains). Polygonization occurs as a result of sliding and climbing of dislocations, as a result of which dislocations of the same sign form "walls" that separate grains into polygons. In a polygonized state, a crystal has less energy than a deformed one, and the formation of polygons is an energetically favorable process. The polygonization start temperature is not constant. The rate of polygonization depends on the nature of the metal, the degree of previous deformation, and the content of impurities. When returning, no noticeable changes in the microstructure are observed, the metal retains its fibrous structure. In this case, the hardness and strength are somewhat reduced, and the ductility increases. Recrystallization. When heated to sufficiently high temperatures, the mobility of atoms increases and the process of recrystallization occurs. Recrystallization is the process of formation and growth of new grains when cold-worked metal is heated to a certain temperature. This process takes place in two stages. There are primary recrystallization (processing) and collective. Primary recrystallization (processing) consists in the formation of nuclei and the growth of new equilibrium grains with an undistorted crystal lattice. It is most likely that new grains appear at the boundaries of blocks and grains, slip packets inside grains, where the metal lattice was most strongly distorted during plastic deformation. The number of new grains gradually increases and, ultimately, no old deformed grains remain in the structure. A deformed metal that is in an unstable state tends to go into a stable state with the smallest amount of free energy. This state corresponds to the process of formation of new grains with an undistorted crystal lattice. In places where the lattice is most distorted and, consequently, the least stable, when heated, the atoms move, the lattice is restored, and the nuclei of new equilibrium grains appear. The nuclei of new grains can also be volumes (blocks) with the least distorted lattice, where atoms pass from neighboring volumes with a distorted lattice. Collective recrystallization - the second stage of the recrystallization process consists in the growth of new grains formed. The driving force of collective recrystallization is the surface energy of the grains. The growth of grains is explained by the fact that in the presence of a large number of small grains, their total surface is very large, so the metal has a large supply of surface energy. With coarsening of grains, the total length of their boundaries becomes smaller, which corresponds to the transition of the metal to a more equilibrium state. With the onset of recrystallization, a significant change in the properties of the metal occurs, opposite to the change in properties during hardening. The strength of the metal decreases. Plasticity, viscosity, thermal conductivity and other properties increase, which decrease during hardening. The properties of the metal are greatly influenced by the size of the grains resulting from recrystallization. The grain size increases with increasing holding time. The largest grains are formed after slight preliminary deformation. This degree of deformation is called critical. Recrystallization annealing. This type of annealing is carried out in order to eliminate hardening of cold-worked metal. The work-hardened metal is very hard and brittle, its crystal lattice is in a non-equilibrium state, having a large reserve of excess free energy. In heavily work-hardened metal, due to the merging of dislocations in the places of their accumulation, dangerous defects are observed - crack nuclei. In some cases, hardening has to be removed. This requires heating, which stimulates diffusion processes. However, recrystallization annealing is more preferable due to the significantly lower temperature and much shorter duration of its implementation with practically the same results. 36. Annealing of the second kind. Annealing and normalization of steels; modes and purpose of annealing and normalization Annealing is the heating and slow cooling of steel. Annealing of the second kind - changing the structure of the alloy in order to obtain equilibrium structures; annealing of the second kind includes complete, incomplete and isothermal annealing. Recrystallization annealing is based on phase recrystallization, i.e., it is annealing of the second kind. Its main purpose is a complete change in the phase composition. The heating temperature and holding time must provide the desired structural transformations, the cooling rate is chosen such that the reverse diffusion phase transformations have time to occur. After annealing, a uniform fine-grained structure is obtained, the hardness decreases, the ductility increases, and type II annealing is used as a preliminary heat treatment and before processing steel parts on machine tools. Depending on the heating temperature, a distinction is made between complete and incomplete annealing. Full annealing is used for hypoeutectoid steel. Products are heated to ensure complete recrystallization - the transformation of the original ferrite-pearlite structure into austenite. Its purpose is to improve the structure of steel to facilitate subsequent processing by cutting, stamping or hardening, as well as to obtain a fine-grained equilibrium pearlite structure in the finished part. Incomplete annealing is associated with phase recrystallization, it is used after hot working by pressure, when the workpiece has a fine-grained structure. After cooling, a rough structure will be obtained, consisting of large grains of ferrite and pearlite. Steel has low ductility. The production of granular cementite is promoted by hot plastic deformation preceding annealing, in which the cementite network is crushed. Steel with granular cementite is better processed by cutting tools and acquires a good structure after hardening. In order to save time, isothermal annealing is carried out. During isothermal annealing, during the holding process, the temperature equalizes over the cross section of the product. This contributes to a more uniform structure and uniform properties. Alloy steels are subjected to such annealing. When annealing alloyed steels, not only the duration of heating and holding increases, but also the duration of cooling. High-alloy steels are cooled at a low rate due to the greater stability of the alloyed austenite. Their hardness remains high after annealing, which impairs the machinability of the cutting tool. Normalization is the heat treatment of steel, in which the product is heated to the austenitic state and cooled in still air. The difference between normalization and full annealing for hypoeutectoid steels is only in the cooling rate. As a result of normalization, a finer structure of the eutectoid is obtained, internal stresses are reduced, defects that have arisen in the process of previous processing of products are eliminated. Hardness and strength are higher than after annealing. Normalization is used as an intermediate operation that improves the structure. The features of this type of heat treatment are the heating temperature and cooling in still air. These features are due to the specific goals of normalization. With regard to hypoeutectoid steels, especially low-carbon steels, normalization in a shorter time and with a greater simplicity of the cooling regime makes it possible to obtain the same results as in annealing. Cooling in air provides a high degree of supercooling of austenite than during annealing, its decomposition products turn out to be more dispersed, and the density of generated dislocations approaches 108 cm2, as a result of which a more favorable fine-grained steel structure with increased strength properties can be obtained by normalization. In some cases, when increased strength properties are not required from the product material, normalization replaces hardening. This is especially true for parts made of low-carbon steel, for which the use of hardening is excluded due to the very high critical speed of hardening. During the normalization of hypereutectoid steels, due to the accelerated separation of excess (secondary) cementite from austenite, an undesirable cementite network around pearlite grains is not formed. In this regard, one of the goals of normalization is the destruction of the mentioned network in hypereutectoid steels. Recrystallization annealing (recrystallization) of steel occurs at temperatures of 500-550 °C; annealing to relieve internal stresses - at temperatures of 600-700 °. These types of annealing relieve internal stresses in castings from uneven cooling of their parts and in workpieces processed by pressure at temperatures below critical. Diffusion annealing is used in cases where intracrystalline segregation is observed in steel. The alignment of the composition in the austenite grains is achieved by the diffusion of carbon and other impurities in the solid state, along with the self-diffusion of iron. As a result, the steel becomes homogeneous in composition (homogeneous), so diffusion annealing is also called homogenization. The homogenization temperature should be high enough, but the grains should not be burned. 37. Vacation of steels. Transformations in steel during tempering, changes in microstructure and properties Tempering is the operation of heating hardened steel to reduce residual stresses and impart a set of mechanical properties that are necessary for long-term operation of the product. Tempering is carried out by heating parts hardened for martensite to a temperature below the critical one. In this case, depending on the heating temperature, the states of martensite, troostite or tempering sorbite can be obtained. These states differ from the states of hardening in structure and properties: during hardening, cementite (in troostite and sorbite) is obtained in the form of elongated plates, as in lamellar perlite. And when you leave it, it turns out to be granular or dotted, as in granular perlite. When tempering steel hardened to martensite, transformations occur in it, which lead to the decomposition of martensite and the formation of an equilibrium structural-phase composition. The intensity and result of these transformations depend on the tempering temperature. The tempering temperature is chosen depending on the functional operational purpose of the product. In the course of many years of operational and production practice, three main groups of products have developed, requiring their "own" specific complexes of viscosity-strength properties for their successful operation. The first group: cutting measuring tools and dies for cold stamping. Their material requires high hardness and a small margin of viscosity. The second group consists of springs and springs, the material of which requires a combination of a high elastic limit with a satisfactory viscosity. The third group includes most machine parts that experience static and especially dynamic or cyclic loads. With long-term operation of products, their material requires a combination of satisfactory strength properties with maximum viscosity. Depending on the heating temperature, there are three types of tempering: low temperature (low), medium temperature (medium) and high temperature (high). The advantage of the dot structure is a more favorable combination of strength and ductility. At low tempering (heating to a temperature of 200-300°C), martensite mainly remains in the steel structure, in addition, the separation of iron carbides from a solid solution of carbon in XNUMX-iron begins and their initial accumulation in small groups. This entails a slight decrease in hardness and an increase in the plastic and ductile properties of steel, as well as a decrease in internal stresses in parts. For low tempering, parts are kept for a certain time, usually in oil or salt baths. Low tempering is used for cutting, measuring tools and gears. With medium and high tempering, steel from the state of martensite passes into the state of troostite or sorbite. The higher the tempering, the lower the hardness of the tempered steel and the greater its ductility and toughness. With high tempering, steel receives a combination of mechanical properties, increased strength, ductility and toughness, therefore, high tempering of steel after quenching it for martensite is called a forging die, springs, springs, and high tempering is for many parts subjected to high stresses. For some steel grades, tempering is carried out after normalization. This refers to fine-grained alloy hypoeutectoid steel (especially nickel) having high toughness and therefore poor machinability by cutting tool. To improve machinability, steel is normalized at elevated temperatures (up to 950-970°), as a result of which it acquires a large structure (which determines better machinability) and at the same time increased hardness (due to the low critical rate of hardening of nickel steel). In order to reduce hardness, this steel is tempered high. The purpose of tempering is not simply to eliminate internal stresses in the hardened steel. At low tempering, martensite is partially freed from the carbon atoms that supersaturate its lattice, and the tempering martensite is based on a supersaturated solid solution of carbon. Medium temperature (medium) tempering is carried out at a temperature of 350 to 450 °C. With such heating, the decomposition of martensite is completed, leading to the formation of ferrite and cementite normal in composition and internal structure. Due to the insufficient intensity of diffusion processes, the grain size of the resulting phases turns out to be very small. High-temperature (high) tempering is carried out at 500-650 °C. Under such heating conditions, with increased diffusion processes, the formation of larger ferrite and cementite grains occurs, accompanied by a decrease in the dislocation density and the complete elimination of residual stresses. The breakdown product of martensite, called temper sorbite, obtained at high tempering, has the highest viscosity for steel. Such a complex is ideal for machine parts subjected to dynamic loads. Due to this advantage, heat treatment combining quenching and high tempering has long been called improvement. 38. Chemical-thermal treatment of steel. Purpose, types and general patterns. Diffusion saturation of alloys with metals and non-metals Chemical-thermal treatment (CHT) - processing with a combination of thermal and chemical effects to change the composition, structure and properties of the surface layer of the part in the required direction, in which the surface saturation of the metal material with the corresponding element (C, T, B, Al, Cr, Si) occurs , T, etc.) by its diffusion in the atomic state from the environment at high temperature. Chemical treatment of metals and alloys, both for the purpose of their surface hardening and protection against corrosion, increases the reliability and durability of machine parts. CTO includes the main interrelated stages: 1) the formation of active atoms in a saturating medium and their diffusion to the surface of the treated metal; 2) adsorption-formed active atoms by the saturation surface; 3) diffusion-movement of adsorbed atoms inside the metal. The development of the diffusion process leads to the formation of a diffusion layer - the material of the part at the saturation surface, which differs from the initial one in chemical composition, structure and properties. The material of the part under the diffusion layer, not affected by the action of the saturating active medium, is called the core. The total thickness of the diffusion layer is the shortest distance from the saturation surface to the core. The effective thickness of the diffusion layer is the shortest distance from the saturation surface to the measured area, which differs by the established limiting nominal value of the basic parameter. The basic parameter of the diffusion layer is a material parameter that serves as a criterion for changing the quality depending on the distance from the saturation surface. The transition zone of the diffusion layer is the inner part of the diffusion layer adjacent to the core, the length of which is determined by the difference between the total and effective thicknesses. Stage XTO - diffusion. In metals, during the formation of substitutional solid solutions, diffusion mainly occurs according to the vacancy mechanism. In the formation of interstitial solid solutions, the mechanism of diffusion along interstices is realized. Carburizing of steel - CTO, which consists in diffusion saturation of the surface layer of steel with carbon when heated in a carburetor, is carried out at 930-950 ° C, when austenite is stable, dissolving carbon in large quantities. For carburizing, low-carbon, alloyed steels are used. Parts are delivered for carburizing after machining with a grinding allowance. The main types of grouting are solid and gas. Gas carburizing is a more advanced technological process than solid carburizing. In the case of gas carburizing, a given concentration of carbon in the layer can be obtained; the duration of the process is reduced; the possibility of full mechanization and automation of the process is provided; simplifies heat treatment of parts. Heat treatment is necessary to: correct the structure and grind the grain of the core and cemented layer; obtain high hardness in the cemented layer and good mechanical properties of the core. After carburizing, the heat treatment consists of double quenching and tempering. The disadvantage of such heat treatment is the complexity of the technological process, the possibility of oxidation and decarburization. The final operation is low tempering at 160-180 °C, which transforms the hardened martensite in the surface layer into tempered martensite, relieving stress and improving mechanical properties. Nitriding of steel - XTO, which consists in diffusion saturation of the surface layer of steel with nitrogen when heated in an appropriate medium. The hardness of the nitrided steel layer is higher than that of the carburized one, and is retained when heated to high temperatures (450-500 °C), while the hardness of the carburized layer, which has a martensitic structure, is maintained up to 200-225 °C. Nitriding is often carried out at 500-600 °C. Diffusion saturation of alloys with metals and non-metals Boriding is the saturation of the surface of metals and alloys with boron in order to increase hardness, wear resistance, and corrosion resistance. Boriding is applied to steels of pearlitic, ferritic and austenitic classes, refractory metals and nickel alloys. Siliconizing. As a result of diffusion saturation of the surface with silicon, the corrosion resistance, heat resistance, hardness and wear resistance of metals and alloys increase. Chrome plating - saturation of the surface of products with chromium. Cast irons, steels of various classes, alloys based on nickel, molybdenum, tungsten, niobium, cobalt and metal-ceramic materials are subjected to diffusion chromium plating. Chrome plating is carried out in vacuum chambers at 1420 °C. Aluminizing is a process of diffusion saturation of the surface of products with aluminum in order to increase heat resistance, corrosion and erosion resistance. When aluminizing iron and steels, a gradual decrease in the aluminum concentration over the layer thickness is observed. The purpose of surface hardening is to increase the hardness, wear resistance and endurance limit of the surface of workpieces. At the same time, the core remains viscous and the product perceives shock loads. 39. Aging. Purpose, change in the microstructure and properties of alloys during aging Tempering and aging are types of heat treatment that change the properties of hardened alloys. The term tempering is usually applied only to those alloys that have been quenched with a polymorphic transformation, and the term aging is used in the case of quenching without a polymorphic transformation (after such quenching, a supersaturated solid solution is fixed). The purpose of steel tempering is to improve its properties. Steel tempering softens the effect of hardening, reduces or removes residual stresses, increases toughness, reduces hardness and brittleness of steel. Tempering is carried out by heating parts hardened for martensite to a temperature below the critical one. In contrast to tempering after aging, strength and hardness increase, and ductility decreases. The main process during aging is the decomposition of a supersaturated solid solution, which is obtained as a result of quenching. Thus, the aging of alloys is associated with a variable solubility of the excess phase, and hardening during aging occurs as a result of dispersed precipitates during the decomposition of a supersaturated solid solution and the resulting internal stresses. In aging alloys, precipitates from supersaturated solid solutions occur in the following main forms: thin-plate (disk-shaped), equiaxed (usually spherical or cubic), and acicular. The energy of elastic distortions is minimal for precipitates in the form of thin plates - lenses. The main purpose of aging is to increase strength and stabilize properties. A distinction is made between natural aging, artificial aging, and after plastic deformation. Natural aging is a spontaneous increase in strength (and decrease in ductility) of a hardened alloy, which occurs in the process of holding it at normal temperature. Heating the alloy increases the mobility of the atoms, which speeds up the process. Solid solutions at low temperatures most often decompose to the stage of zone formation. These zones are dispersed regions that are enriched with an excess component. They retain the crystalline structure that the original solution had. The zones are named after Guinier and Preston. Using electron microscopy, these zones can be observed in Al - Ag alloys, which have the form of spherical particles with a diameter of ~10 A. Al-Cu spalavs have zone-plates that have a thickness of <10A. Artificial aging is an increase in strength that occurs during exposure to elevated temperatures. If a hardened alloy having the structure of a supersaturated solid solution is subjected to plastic deformation, then this accelerates the processes occurring during aging. This type of aging is called deformation. Heat treatment of aluminum alloys consists of two cycles - hardening and aging. Aging encompasses all the processes that occur in a supersaturated solid solution - the processes that prepare the release, and the processes of release. A transformation in which only precipitation processes occur is called precipitation hardening. For practice, the incubation period is of great importance - the time during which preparatory processes are performed in the hardened alloy, the time during which the hardened alloy retains high ductility. This makes it possible to carry out cold deformation immediately after quenching. If only precipitation processes occur during aging, without complex preparatory processes, then this phenomenon is called precipitation hardening. The practical significance of the phenomenon of aging of alloys is very high. So, after aging, the strength increases and the ductility of low-carbon steel decreases as a result of dispersed precipitation in ferrite of tertiary cementite and nitrides. Aging is the main way to harden aluminum alloys, some copper alloys, and many high-temperature and other alloys. At present, maraging alloys are being used more and more widely. Today, quite often, instead of the term "natural aging", the term "low-temperature aging" is used, and instead of "artificial aging" - "high-temperature aging". The very first metals to be hardened by aging were aluminum alloys. Hardening was carried out at temperatures above 100 °C. Differences in the decomposition process are observed in different temperature intervals. Therefore, to obtain an optimal set of properties in alloys, complex aging is used, which takes place in a certain sequence, at low and higher temperatures. The aging of alloys, caused by the process of decomposition of a saturated solid solution, is the most important. After cooling of the alloys, a state of supersaturation of the solid solution appears. This is due to the fact that at high temperatures the solubility of impurities and alloying components increases. 40. Classification and marking of alloyed steels. Influence of alloying elements on transformations, microstructure and properties of steel; principles for the development of alloy steels Alloy steel is steel that contains, in addition to carbon and conventional impurities, other elements that improve its properties. Chromium, nickel, manganese, silicon, tungsten, molybdenum, vanadium, cobalt, titanium, aluminum, copper and other elements are used for alloying steel. Manganese is considered an alloying component only when its content in steel is more than 1%, and silicon - when the content is more than 0,8%. Alloying elements are introduced into the steel, which change its mechanical, physical and chemical properties, and, depending on the purpose of the steel, elements are introduced into it that change the properties in the right direction. Alloy steel of many grades acquires high physical and mechanical properties only after heat treatment. According to the total amount of alloying elements contained in steel, it is divided into low-alloyed (total content of alloying elements is less than 2,5%), medium-alloyed (from 2,5 to 10%) and high-alloyed (more than 10%). The disadvantage of carbon steel is that this steel does not have the desired combination of mechanical properties. With an increase in carbon content, strength and hardness increase, but at the same time, ductility and toughness sharply decrease, and brittleness increases. Carbon steel cutting tools are very brittle and unsuitable for impact loading operations on the tool. Carbon steel often fails to meet the requirements of responsible machine building and tool making. In such cases it is necessary to use alloyed steel. Alloying elements in relation to carbon are divided into two groups: 1) elements that form stable chemical compounds with carbon - carbides (chromium, manganese, molybdenum, tungsten, titanium); carbides can be simple (for example, Cr4 C) or complex alloyed ones (for example, ((FeСг)7С3); their hardness is usually higher than the hardness of iron carbide, and their brittleness is lower; 2) elements that do not form carbides in the presence of iron and are included in the solid solution - ferrite (nickel, silicon, cobalt, aluminum, copper). By appointment, alloyed steel is divided into structural, tool and steel with special physical and chemical properties. Structural steel is used for the manufacture of machine parts; it is divided into cemented (subjected to cementation) and improved (subjected to improvement - quenching and high tempering). Steels with special properties include: stainless, heat-resistant, acid-resistant, wear-resistant, with special magnetic and electrical properties. Marking according to GOST for the designation of alloying elements: X - chromium, H - nickel, G - manganese, C - silicon, B - tungsten, M - molybdenum, K - cobalt. For structural alloyed steel, a marking is adopted, according to which the first two digits show the average carbon content in hundredths of a percent, the letters show the presence of the corresponding alloying elements, and the numbers following the letters show the percentage of these components in the steel. If there is no number after any letter, then the content of this element in steel is approximately equal to 1%. If the figure is missing, then the steel contains about or more than 1% carbon. To designate high-quality steel, the letter A is added at the end of the marking. High-quality steel contains less sulfur and phosphorus than ordinary high-quality steel. Special purpose steels have a special marking of the letters that are placed in front: Ш - ball bearing, Р - high-speed cutting, Zh - chromium stainless ferritic class, Я - chromium-nickel stainless austenitic class, E - electrical steel. Many steels can be attributed to engineering materials that have sufficiently high strength properties. Such steels include: carbon steels, low-alloy steels, high-strength medium-alloyed steels, high-strength high-alloyed (martensitically aging) steels. All alloyed steels can be divided into groups depending on four features: according to the equilibrium structure of the steel, according to the structure after cooling the steel in air, according to the composition of the steel, according to the purpose of the steel. Depending on how much carbon is contained in steel, the following types are distinguished: low-carbon up to 0.1-0.2%, medium-carbon and high-carbon 0.6-1.7% C. The structure of steels can be hypoeutectoid (ferrite + pearlite), eutectoid (pearlite) and hypereutectoid (pearlite + cementite) steel. There are three ways of smelting steel: boiling, semi-calm, calm methods. With the boiling method, the steel structure contains a large number of gas bubbles, which are the result of steel deoxidation in the molds and CO evolution. Steels are also obtained using converters, electric furnaces, and continuous casting installations. 41. Structural steels: construction, engineering, high-strength. Tool steels: tool steels, bearing steels, die steels Carbon tool steels U8, U10, U11, U12, due to the low stability of supercooled austenite, have low hardenability, they are used for small tools. Steels U10, U11, U12 are used for cutting tools (drills, files), U7 and U8 - for woodworking tools. Steels can be used as a cutting tool only for cutting at low speed, since their high hardness (U10-U12-62-63НРС) is greatly reduced when heated above 190-200 °C. Alloy steels with increased hardenability that do not have heat resistance (11HF, 13X, HVSG, 9XS, X, V2F) are suitable for cutting materials of low strength, they are used for tools that are not subjected to heat during operation. Alloy steels have higher hardenability than carbon steels. High-speed steels (R6M5, R12F3, R8M3) have high heat resistance and have high hardness, strength and wear resistance at elevated temperatures that occur in the cutting edge when cutting at high speed. The main alloying elements of these steels are tungsten, molybdenum, cobalt and vanadium. Carbon steel is divided into structural (soft and medium hard steel) and tool (hard) steel. Structural steel according to GOST is divided into: 1) carbon steel of ordinary quality, hot-rolled, smelted by the open-hearth or Bessemer method; 2) high-quality carbon steel, machine-building, hot-rolled and forged, smelted in open-hearth or electric furnaces. This steel is used for the manufacture of more critical parts of machines and mechanisms. Structural alloyed steel is used for the manufacture of critical machine parts and metal structures. Triple alloy steel. Chromium as an alloying component increases the strength of steel and is relatively cheap. Chromium gives steel good wear resistance, and with an increase in the amount of carbon - high hardness due to the formation of carbides. Low- and medium-alloy chromium steel is widely used in aircraft, auto and tractor construction, as well as in other branches of engineering for the manufacture of axles, shafts, gears and other parts. Chrome steel with a content of 0,4-1,65% Cr and 0,95-1,15% C forms a group of ball bearing steels. Low-alloy chromium steel is also used for the manufacture of tools. High-alloy chromium steel is stainless and is resistant to corrosion not only in air, but also in aggressive environments. It retains strength at elevated temperatures and is used for the manufacture of turbine blades, high-pressure cylinders, and superheater tubes. Nickel is an excellent alloying element, but it is very expensive and scarce. They try to use it in combination with chromium and manganese. Nickel increases the strength, toughness and hardness (after quenching) of steel, slightly reducing ductility, and greatly increasing hardenability and corrosion resistance. After quenching and low tempering, nickel steel has high hardness but no brittleness. Low- and medium-alloyed nickel steel is used in the automotive and critical engineering industries. High alloy nickel steel has special properties. With a silicon content of more than 0,8%, the strength, elasticity and hardness of steel increase, reducing its toughness. Low carbon silicon steel is used for bridge construction and is not subjected to heat treatment. Steel 55C2, 6 °C2 is used for the manufacture of springs and springs. After quenching and tempering, this steel has a high tensile strength and elasticity. Manganese increases the hardness and strength of steel, increases its hardenability and improves weldability. Alloyed manganese steel is called steel, which contains at least 1% Mn. In practice, low-alloy and high-alloy manganese steel is used. High-alloy steel grade G13, which has a very high toughness and resistance to impact abrasion, has become widespread: it is used to make railway switches and crosses, dredger visors. Tool alloy steel. For each type of tool, it is necessary to use the steel that is most suitable in terms of its qualities for the given working conditions. Low-alloy steel for cutting tools does not differ in its cutting ability from carbon steel and is used at low cutting speeds. Common grades of low alloy steel for cutting tools are: 1) steel grade X - chromium (for the manufacture of cutters, drills); 2) steel grade 9XC - chromium-silicon (for the manufacture of cutters, drills); 3) steel grade B1 - tungsten (for the manufacture of twist drills, reamers). 42. Stainless, heat-resistant and heat-resistant, cold-resistant, electrical and wear-resistant steels The corrosion resistance of steel increases if the carbon content is reduced to the minimum possible amount and an alloying element is introduced that forms solid solutions with iron in such an amount that the electrode potential of the alloy increases. Steel that is resistant to atmospheric corrosion is called stainless steel. Steel or an alloy that has high resistance to corrosion by acids, salts, alkalis and other aggressive media is called acid-resistant. Corrosion is the destruction of metals due to the interaction of their electrochemical interaction with the environment. Structural materials have high corrosion resistance. Carbon and low alloy steels are unstable against corrosion in the atmosphere, water and other media. Corrosion-resistant are metals and alloys that are able to resist the corrosive effects of the environment. Chromium is the main alloying element that makes steel corrosion-resistant in oxidizing environments. Heat resistance is the ability of metals and alloys to resist the corrosive effects of gases at high temperatures. The corrosive effect of gases leads to the oxidation of steel at high temperatures. The intensity of oxidation is affected by the composition and structure of the oxide film. If the film is porous, then oxidation occurs intensively, if it is dense, it slows down or stops altogether. To obtain a dense oxide film, which prevents the penetration of oxygen deep into the steel, it is alloyed with chromium, silicon or aluminum. The more alloying element in steel, the higher its heat resistance. Heat resistance. For a tool material, it is determined by the highest temperature at which it retains its cutting properties. The heat resistance of the used tool materials ranges from 200 to 1500 ° C. According to the degree of decrease in heat resistance, the materials are arranged in the following order: superhard, cutting ceramics, hard alloys, high-speed, alloyed, carbon steels. Even when exposed to temperatures for a long time, high heat-resistant properties must remain at the same level. The metal of the hot dies must offer stable tempering resistance. Heat resistance is the ability of steel to resist mechanical stress at high temperatures. Heat-resistant steels and alloys are those that can work under load at high temperatures for a long time. Heat-resistant steels are usually heat-resistant at the same time. Creep is a deformation that increases under prolonged action of constant load and high temperature. For carbon and alloy structural steels, creep occurs at temperatures above 350 °C. Creep is characterized by the creep limit, which is understood as the stress that causes the steel to deform by a certain amount in a certain time at a given temperature. Heat resistant alloys. The development of heat-resistant nickel alloys began with small additions of titanium and aluminum to ordinary nichrome. The addition of less than 2% titanium and aluminum without heat treatment significantly increases the creep performance of nichrome at temperatures around 700 °C. Heat-resistant nickel alloys are divided into wrought and cast alloys. The heat-resistant properties of wrought alloys are formed during heat treatment. Cast high-temperature nickel alloys are similar in composition to wrought alloys, but usually contain a larger amount of aluminum and titanium. Cold resistance - the ability of a metal to resist deformation and destruction, which can occur under the influence of low temperatures. Electrical steel is a thin sheet of mild steel. The cores of electrical equipment are made from it. This steel contains silicon. There are cold-rolled and hot-rolled electrical steel, as well as dynamo and transformer steel. For alloying electrical steel, 0,5% Al is used. Wear resistant steel. For parts operating under conditions of abrasive wear, high pressures and impacts (tracks of caterpillar vehicles, jaws of crushers, switch points of railway and tram tracks), high-manganese cast steel 110G13L of austenitic structure containing 0,9% C and 11,5% Mn is used. In the cast state, the steel structure consists of austenite and carbides of the (Fe, Mn)3C type, which precipitate along the boundaries of austenite grains, and its strength and impact strength are greatly reduced, so the cast parts are subjected to quenching with heating up to 1100 ° C and cooling in water. At this temperature, the carbides dissolve in the austenite and the steel acquires a more stable austenitic structure. Under conditions of impact and abrasive wear, defects in the crystalline structure (dislocations, stacking faults) are formed in the surface layer of the steel, which leads to surface hardening. An increase in hardness and wear resistance as a result of work hardening is possible under impact loads and cold plastic deformation. Due to hardening, steel 110G13L is poorly machined by cutting, so it is advisable to manufacture parts or products from this steel by casting without subsequent machining. The letter L at the end of the brand of this steel means "casting". 43. Marking, structure, properties and applications of non-ferrous metals and their alloys Non-ferrous metals include copper, aluminium, magnesium, titanium, lead, zinc and tin, which have valuable properties and are used in industry despite their relatively high cost. Sometimes, when possible, non-ferrous metals are replaced with ferrous metals or non-metallic materials (eg, plastics). The following groups of non-ferrous metals and alloys are distinguished: light metals and alloys (with a density of 3.0 g/cm3); copper alloys and special non-ferrous alloys - cupronickel, non-silver, precious alloys, etc. In the application industry, copper occupies one of the first places among non-ferrous metals. Properties of copper - high ductility, electrical conductivity, thermal conductivity, increased corrosion resistance. Copper is used in electrical engineering, the manufacture of cables and wires for the transmission of electricity, and serves as the basis for the manufacture of various alloys widely used in mechanical engineering. Aluminum is a light metal that has high ductility, good electrical conductivity and corrosion resistance. It is used for the manufacture of electrical wires, utensils, for the protection of other metals and alloys from oxidation by cladding. In mechanical engineering, pure aluminum is rarely used, because it has low mechanical properties. Aluminum is the basis for the production of many alloys widely used in aircraft construction, car and carriage building, and instrument making. Aluminum alloys are deformed (hardened by heat treatment and not hardened) and cast. Duralumin is the most common alloy, which is used in a deformed form and is strengthened by heat treatment. Magnesium is the most common metal and is silvery white in color. The great advantage of magnesium is that it is a very light metal. The main disadvantage is its low corrosion resistance. Pure magnesium has not found distribution in technology, but is used as a basis for the production of light alloys. The following grades of non-ferrous metals (GOST) have been established: aluminum - AB1, AB2, AOO, AO, A1, A2 and A3; copper - MO, M1, M2, ME, M4; tin - 01, 02, OE and 04; lead - CB, CO, C1, C2, C3, C4; zinc - TsV, TsO, Ts1, Ts2, Ts3, Ts4; magnesium - Mg1, Mg2. Brass. Compared to pure copper, brass has greater strength, ductility and hardness, they are more fluid and corrosion resistant. In addition to simple brass, special brasses with additions of iron, manganese, nickel, tin, and silicon are used. The amount of alloying components in special brass does not exceed 7-8%. Special brasses have improved mechanical properties; some of them are not inferior in strength to medium carbon steel. According to GOST, brass is designated by the letter L and a number that indicates the amount of copper in the alloy. The designation of alloying components is as follows: F - iron; H - nickel; O - tin; K - silicon; C - lead. The amount of the alloying component is indicated in numbers. Brasses are foundry (used for shaped casting) and subjected to pressure treatment. Brass is used for the manufacture of sheets, wire, sleeves, stamped fittings, utensils. Bronzes are: tin, aluminum, silicon, nickel. Tin bronzes have high corrosion resistance, good fluidity and enhanced antifriction properties. Castings are made from them. Simple tin bronzes are rarely used, since the introduction of additional elements (zinc, lead, nickel) can achieve better properties with a lower content of scarce tin. According to GOST, tin bronzes are marked with the letters BrO and a number that indicates the content of tin; subsequent letters and numbers show the presence and quantity of additional elements in the bronze. To designate additional elements, the same letters are used as when marking special brass; zinc is denoted by the letter C, and phosphorus by the letter F. Tin is an expensive metal and is rarely used in practice. Substitutes for tin bronze are aluminum, silicon, manganese and other bronzes. Aluminum bronze is used with a content of up to 11% A1. By structure, bronze is mainly (up to 9,7% Al) single-phase and is a solid solution of aluminum in copper. In terms of mechanical properties, aluminum bronze is better than tin bronze, it has ductility, corrosion resistance and wear resistance. The disadvantage is a large shrinkage during cooling from a liquid state, as well as in the easy formation of aluminum oxides in liquid bronze, which impairs its fluidity. Additional elements (iron, manganese) increase its mechanical properties. Silicon bronze belongs to homogeneous alloys - solid solutions, has high mechanical and casting properties. Replaces tin bronze. Manganese and nickel are introduced into silicon bronzes to improve their properties. 44. Aluminum; the influence of impurities on the properties of aluminum; wrought and cast aluminum alloys Aluminum is distinguished by low density, high thermal and electrical conductivity, good corrosion resistance in many environments due to the formation of a dense Al oxide film on the metal surface.203. Technical annealed aluminum ADM is hardened by cold plastic deformation. Aluminum is highly ductile and easily processed by pressure, however, when cutting, complications arise, one of the reasons for which is sticking of the metal to the tool. Depending on what impurities are present in aluminum, changes in its corrosion, physical, mechanical and technological properties are observed. Most impurities adversely affect the electrical conductivity of aluminum. The most common impurities are iron, silicon. Iron, along with electrical conductivity, reduces ductility and corrosion resistance, and increases the strength properties of aluminum. The presence of iron in alloys of aluminum with silicon and magnesium adversely affects the properties of the alloy. Only in those aluminum alloys where nickel is present, iron is considered a useful impurity. The most common impurity in aluminum alloys is silicon. This metal, as well as copper, magnesium, zinc, manganese, nickel and chromium, are introduced into aluminum alloys as the main components. CuAl compounds2, mg2Si, CuMgAl2- effectively strengthen aluminum alloys. Basic alloying elements in aluminum alloys. Manganese improves corrosion resistance. Silicon is the main alloying element in a number of cast aluminum alloys (silumins), since it participates in the formation of eutectics. Ni, Ti, Cr, Fe increase the heat resistance of alloys, inhibiting diffusion processes and forming stable complexly alloyed hardening phases. Lithium in alloys contributes to an increase in their modulus of elasticity. At the same time, magnesium and manganese reduce the thermal and electrical conductivity of aluminum, and iron - its corrosion resistance. Marking of aluminum alloys. Currently, two alloy markings are used simultaneously: the old alphanumeric and the new digital. Along with this, there is an alphanumeric marking of the technological processing of semi-finished products and products, which qualitatively reflects the mechanical, chemical and other properties of the alloy. Classification of aluminum alloys. Aluminum alloys are mainly divided into wrought and cast aluminum alloys, since plastic deformation and casting processes are used in the production of powder alloys and composite materials. Aluminum alloys are divided according to their ability to be hardened by heat treatment into hardened and non-hardened. They can be subjected to homogenization, recrystallization and softening annealing. Alloys of the Al-Cu-Mg system - duralumins D1, D16, D18, D19, etc. are distinguished by a good combination of strength and ductility. Heat treatment strengthens duralumins, increases their weldability by spot welding. They can be machined satisfactorily, but are prone to intergranular corrosion after heating. A significant increase in the corrosion resistance of alloys is achieved by cladding. In aviation, duralumins are used for the manufacture of propeller blades (D1), power elements of aircraft structures (D16, D19). High-strength alloys of the Al-Zn-Mg-Cu system (V93, V95, V96Ts) are characterized by high values of tensile strength (up to 700 MPa). At the same time, sufficient plasticity, crack resistance and corrosion resistance are achieved by coagulation stepwise aging (T2, T95), as well as by using alloys of high (V95kch) and special (VXNUMXoch) purity. The high-modulus alloy 1420, due to the alloying of aluminum with lithium and magnesium (Al-M-Li system), has a reduced (by 11%) density and at the same time an increased (by 4%) elastic modulus. Forging alloys AK6 and AK8 (Al-M-Si-Cu system) have high plasticity during hot working. They are satisfactorily welded, well machined, but prone to corrosion under stress. To ensure corrosion resistance, parts made of AK6 and AK8 alloys are anodized or coated with paints and varnishes. Forging alloys are used to make forged and stamped aircraft parts that work under load. These alloys are capable of operating at cryogenic temperatures. Heat-resistant aluminum alloys of the A1-Cu-Mn (D20, D21) and Al-Cu-Mg-Fe-Ni (AK4-1) systems are used for the manufacture of parts (pistons, cylinder heads, disks) operating at elevated temperatures (up to 300 ° C). Heat resistance is achieved by alloying alloys with nickel, iron and titanium, which inhibit diffusion processes and form complexly alloyed finely dispersed strengthening phases that are resistant to coagulation upon heating. Alloys have high ductility and workability in the hot state. Cast aluminum alloys. The main requirements for alloys for shaped castings are a combination of good casting properties (high fluidity, low shrinkage, low hot cracking and porosity) with optimal mechanical and chemical (corrosion resistance) properties. Eutectic alloys have the best casting properties. 45. Copper; influence of impurities on the properties of copper. Brass, bronze, copper-nickel alloys Copper is a red metal, in a pink fracture, has a melting point of 1083 ° C. The FCC crystal lattice with a period of 0,31607 pits. The density of copper is 8,94 g/cm3. Copper has high electrical and thermal conductivity. The specific electrical resistance of copper is 0,0175 μOhm m. Copper grades: M00 (99,99% Cu), MO (99,97% Cu), M1 (99,9% Cu), M2 (99,7% Cu), M3 (99,50% Cu). The impurities present in copper have a great influence on its properties. According to the nature of the interaction of impurities with copper, they can be divided into three groups. 1. Impurities that form solid solutions with copper: Ni, Zn, Sb, Fe. P and others. These impurities (especially Sb) sharply reduce the electrical conductivity and thermal conductivity of copper, therefore copper M0 and M1 are used for current conductors. Antimony makes hot working difficult. 2. Impurities Pb, Bi and others, practically insoluble in copper, form low-melting eutectics in it, which, separating along the grain boundaries, make it difficult to process by pressure. At a content of 0,005% Bi, copper is destroyed during hot working by pressure; at a higher bismuth content, copper becomes cold brittle; these impurities have little effect on the electrical conductivity. 3. Impurities of oxygen and sulfur, forming brittle chemical compounds Cu with copper2O and Cu2S, which are part of the eutectic. If oxygen is in solution, then it reduces the electrical conductivity, and sulfur does not affect it. Sulfur improves the machinability of copper by cutting, and oxygen, if present in copper, forms cuprous oxide and causes "hydrogen disease". When copper is heated in an atmosphere containing hydrogen, it diffuses into the depth of copper. If there are Cu inclusions in copper2Oh, they react with hydrogen, resulting in the formation of water vapor. Two main groups of copper alloys: brass - alloys of copper with zinc; bronzes are alloys of copper with other elements. Brass is a multi-component alloy based on copper, where the main component is zinc. Technical brasses contain up to 40-45% Zn. Single-phase b-brass, which are easily deformed in cold and hot conditions, include L96 (tompak), L80 (half-tompak), L68, which has the highest ductility. Two-phase (α + β) - brass, L59 and L60 are less ductile in the cold state and are subjected to hot pressure treatment. On the basis of technology, brass is divided into two groups: deformed and foundry. Cast brasses are not very prone to liquidation and have anti-friction properties. Wrought brasses have high corrosive properties in atmospheric conditions. Brass, intended for shaped casting, contain a large number of special additives that improve their casting properties. Tin bronzes. Alloys rich in tin are very brittle. Tin bronzes are usually alloyed with Zn, Pe, P, Pb, Ni and other elements. Zinc improves the technological properties of bronze and reduces the cost of bronze. Phosphorus improves casting properties. Nickel increases the mechanical properties, corrosion resistance and density of castings and reduces segregation. Iron grinds grain, but worsens the technological properties of bronzes and corrosion resistance. There are wrought and cast tin bronzes, which have good casting properties. Two-phase bronzes have high antifriction properties. They are used for the manufacture of anti-friction parts. Nickel alloys are widely used in mechanical engineering. Nickel gives copper increased resistance to corrosion and improves its mechanical and casting properties. Bronzes that contain only nickel are not used due to the high cost of nickel. Nickel is introduced in combination with other elements. Nickel alloys are common in industry, which have the following names: cupronickel (copper alloy with 18-20% nickel) - used for sleeves, has a white color and high corrosion resistance; constantan is an alloy of copper with 39-41% nickel. Constantan has a high electrical resistance and is used in the form of wires and tapes for rheostats, electrical measuring instruments. Copper and its alloys are widely used in electrical engineering, electronics, instrumentation, foundry, and engine building. Thus, 50% of the produced copper is consumed by the electrical and electronic industries. It is in second place (after aluminum) in terms of production among non-ferrous metals. Technical and technological properties of copper: high electrical and thermal conductivity, sufficient corrosion resistance, good workability by pressure, weldability by all types of welding, good solderability, easy polishing. Pure copper has low strength and high ductility. The disadvantages of copper include: - high price; - significant density; - large shrinkage during casting; - hot brittleness; - the complexity of cutting. 46. Magnesium and its alloys Magnesium is a reactive metal: the MgO oxide film formed in air, due to its higher density than that of magnesium itself, cracks and has no protective properties; magnesium powder and shavings are highly flammable; hot and molten magnesium explodes on contact with water. Magnesium and its alloys are poorly resistant to corrosion, have low fluidity during casting, and are plastically deformed only at elevated temperatures (225 °C or more). The latter is due to the fact that the shift in the hexagonal lattice of magnesium at low temperatures occurs only along the basis plane (the base of the hexagonal prism). Heating to 200-300 °C leads to the appearance of additional slip planes and, accordingly, an increase in plasticity. The low diffusion mobility of atoms in magnesium alloys slows down phase transformations in them. Therefore, heat treatment (diffusion or recrystallization annealing, hardening, aging) requires long exposures (up to 24 h). At the same time, magnesium alloys are characterized by high specific strength, absorb vibrations well, and do not interact with uranium. They are well processed by cutting and are satisfactorily welded by argon-arc and contact welding. The main alloying elements in magnesium alloys are Mn, Al and Zn. Manganese increases the corrosion resistance and weldability of magnesium alloys. Aluminum and zinc have a great influence on the strength and ductility of magnesium alloys: the maximum values of mechanical characteristics are achieved when 6-7% aluminum or 4-6% zinc is introduced into the alloy. These elements (Al, Zn) form hardening phases with magnesium, which precipitate in a finely dispersed form after quenching with aging. Zirconium, titanium, alkaline earth (Ca) and rare earth (Ce, 1a) metals and thorium grind the grain, deoxidize the alloy, and increase its heat resistance. According to the manufacturing technology of products, magnesium alloys are divided into foundry (marking "ML") and wrought ("MA"). Magnesium alloys are subjected to various types of heat treatment. So, to eliminate segregation in cast alloys (dissolving excess phases released during casting and equalizing the chemical composition by grain volume), diffusion annealing (homogenization) of shaped castings and ingots is carried out (400–490 °C, 10–24 h). Hardening is removed by recrystallization annealing at 250-350 "C, during which the anisotropy of mechanical properties that has arisen during plastic deformation also decreases. Magnesium alloys, depending on the composition, can be hardened by quenching (often with cooling in air) and subsequent aging at 150-200 ° C (Tb mode). A number of alloys are hardened already in the process of cooling castings or forgings and can immediately be hardened by artificial aging (bypassing hardening). But in most cases, they are limited only to homogenization (quenching) at 380–540 °C (T4 mode), since subsequent aging, increasing strength by 20–35%, leads to a decrease in the ductility of the alloys. Cast alloys. In cast magnesium alloys, an increase in mechanical properties is achieved by grinding the grain by overheating the melt or modifying it with chalk or magnesite additives. In this case, solid particles are formed in the melt, which become centers of crystallization. To prevent ignition of magnesium alloys, they are melted in iron crucibles under a layer of flux, and poured in sulfur dioxide vapors formed when sulfur is introduced into the metal stream. When casting in sand molds, special additives (aluminum fluorides) are introduced into the mixture to reduce the oxidation of magnesium. Among cast magnesium alloys, alloys ML5 and ML6, which are distinguished by increased casting and mechanical properties, are widely used. They can be hardened both by homogenization and quenching in air (T4) and by additional aging (T6). wrought alloys. Deformed (pressed) magnesium has a higher set of mechanical properties than cast magnesium. Wrought alloys are produced in the form of forgings, die blanks, hot-rolled strips, bars and profiles. The temperature ranges of technological processes of magnesium alloys forming are within the following limits: pressing at 300-480 °C, rolling at 440-225 °C and stamping (in closed dies) at 480-280 °C. Good corrosion resistance, weldability and technological ductility are distinguished by MA1 alloy, which belongs to the group of low strength alloys. Alloy MA2-1 combines an optimal set of mechanical and technological properties (well welded, stamped), but is subject to corrosion under stress. Heat-resistant (up to 250 °C) is an alloy of the system (Md-Zn-Zr) MA14. The alloy is hardened by artificial aging (T5 mode) after pressing and cooling in air. It is characterized by increased mechanical properties, but is prone to the formation of hot cracks during rolling. The use of magnesium alloys. Magnesium alloys are used to make rocket bodies, pumps, instruments, fuel and oxygen tanks, engine frames, casings. So, ML5 and ML6 alloys are used for casting brake drums, steering wheels, gearboxes, ML10 - parts of high-tightness devices. Fittings, gasoline and oil systems, as well as welded parts are made of wrought alloys MA1, highly loaded parts - from MA14. 47. Titanium and its alloys Titanium and alloys based on it have high corrosion resistance and specific strength. Disadvantages of titanium: its active interaction with atmospheric gases, the tendency to hydrogen embrittlement. Nitrogen, carbon, oxygen and hydrogen, strengthening titanium, reduce its ductility, corrosion resistance, and weldability. Titanium is poorly machined by cutting, satisfactorily by pressure, welded in a protective atmosphere. Vacuum casting has become widespread, including vacuum-arc remelting with a consumable electrode. Allotropic modifications of titanium: low-temperature and high-temperature. There are two main groups of alloying elements depending on their effect on the titanium polymorphic transformation temperature (882,5 ° C): b-stabilizers (elements that expand the region of existence of the b-phase and increase the transformation temperature - A1, Oa, C) and c- stabilizers (elements that narrow the b-region and reduce the temperature of the polymorphic transformation - V, Mo, Cr). Alloying elements are divided into two main groups: elements with large (in the limit - unlimited) and limited solubility in titanium. Elements with limited solubility, together with titanium, can form intermetallic compounds, silicides, and interstitial phases. Alloying elements affect the operational properties of titanium (Fe, Al, Mn, Cr), increase its strength, but reduce elasticity and toughness; Al, Zr increase the heat resistance, and Mo, Zr, Ta - corrosion resistance. Classification of titanium alloys. The structure of industrial titanium alloys is solid solutions of alloying elements in b- and b-modifications of titanium. Types of heat treatment of titanium alloys. Recrystallization (simple) annealing of cold-formed alloys (650-850 °C). Isothermal annealing (heating to 780-980 °C followed by cooling in a furnace to 530-680 °C, holding at this temperature and cooling in air), providing high ductility and thermal stability of the alloys. Double stepped annealing (it differs from isothermal in that the transition from the first stage to the second is carried out by cooling the alloy in air, followed by reheating to the temperature of the second stage), which leads to strengthening of the alloy and a decrease in plasticity due to the partial occurrence of hardening and aging processes. Partial annealing at 500-680 °C in order to relieve residual stresses arising during machining. Hardening heat treatment. Most titanium alloys are alloyed with aluminum, which increases the rigidity, strength, heat resistance and heat resistance of the material, and also reduces its density. α-titanium alloys are not hardened by heat treatment; their hardening is achieved by solid solution alloying and plastic deformation. (α + β) - titanium alloys are characterized by a mixed structure and are hardened by heat treatment, consisting of hardening and aging. Pseudo-β-titanium alloys are characterized by a high content of β-stabilizers and the resulting absence of martensitic transformation. The alloys are characterized by high ductility in the hardened state and high strength in the aged state; they are satisfactorily welded by argon arc welding. Cast titanium alloys. Compared with wrought alloys, cast alloys have lower strength, ductility, and endurance, but are cheaper. The complexity of casting titanium alloys is due to the active interaction of titanium with gases and molding materials. Casting alloys VT5L, VT14L and VTZ-1L basically coincide in composition with similar wrought alloys (at the same time, the VT14L alloy additionally contains iron and chromium). The VT5L alloy has high technological properties: it is ductile, not prone to cracking during casting, and welds well. Shaped castings from VT5L alloy operate at temperatures up to 400 °C. The disadvantage of the alloy is its low strength (800 MPa). the two-phase casting alloy VT14L is annealed at 850°C instead of hardening heat treatment, which drastically reduces the plasticity of castings. Powder titanium alloys. The use of powder metallurgy methods for the production of titanium alloys makes it possible, with the same operational properties as that of a cast or deformable material, to achieve a reduction of up to 50% in the cost and time of manufacturing products. Titanium powder alloy VT6 obtained by hot isostatic pressing (HIP) has the same mechanical properties as the wrought alloy after annealing. To the hardened and aged wrought alloy VT6, the powder alloy is inferior in strength, but superior in ductility. The use of titanium alloys: plating of aircraft, ships, submarines; shells of missiles and engines; disks and blades of stationary turbines and compressors of aircraft engines; propellers; cylinders for liquefied gases; containers for aggressive chemical environments, etc. 48. Types of composite materials. Structure, properties, applications Composite materials consist of two components combined in various ways into a monolith while maintaining their individual characteristics. Material features: - the composition, shape and distribution of the components are predetermined; - consist of two components and more different chemical composition, separated by a boundary; - has properties that are different from the properties of the components taken separately; - homogeneous on the macroscale and heterogeneous on the microscale; - does not occur in nature, man-made. The components of the material are different geometrically. A matrix is a component that has continuity throughout its volume. The filler is a discontinuous, reinforcing component. In composite materials, metals and their alloys, organic and inorganic polymers, and ceramic materials are used as matrices. The properties depend on the physicochemical properties of the components and the strength of the bond between them. Components for a composite material are selected with properties that differ from each other. Such materials have high specific rigidity and specific strength. Common composite materials with zero-dimensional fillers are a metal matrix made of metal or alloy. Composite materials with a uniform distribution of hardener particles are distinguished by isotropic properties. Compositions reinforced with dispersed particles are obtained by powder metallurgy methods. Composite materials with an aluminum matrix based on aluminum are strengthened by A1203 particles, obtained by pressing aluminum powder with subsequent sintering (SAP). SAP alloys are satisfactorily deformed in the hot state, and SAP-1 alloys are deformed in the cold state as well. SAP is easily processed by cutting, satisfactorily welded by argon-arc and resistance welding. Semi-finished products are produced from SAP in the form of sheets, profiles, pipes, foil. Composite materials with a nickel matrix. The hardening component is toxic particles of thorium dioxide (TI02) or hafnium dioxide (Hf02). These materials are designated VDU-1 and VDU-2, respectively. Composite materials VDU-1 and VDU-2 are plastic, deformed in a wide temperature range by various methods (forging, stamping, upsetting, deep drawing). To connect parts made of alloys of the VDU type, high-temperature soldering or diffusion welding is used to prevent melting. VDU-2 alloys are used in aircraft engine building. Composite materials with one-dimensional fillers are strengthened by means of one-dimensional elements in the form of whiskers, fibers (wires). The fibers are held together by a matrix into a single monolith. The matrix serves to protect the reinforcing fiber from damage, is a medium that transfers the load to the fibers, and redistributes stresses in the event of rupture of individual fibers. Composite materials on a nickel matrix Heat-resistant nickel alloys are subjected to reinforcement in order to increase their operating time and operating temperature up to 1100-1200 °C. To reinforce nickel alloys, hardeners are used: whiskers, wires of refractory metals and alloys, carbon fibers and silicon carbide. Eutectic composite materials - alloys of eutectic composition. In them, the strengthening phase is oriented crystals, which are formed during directional crystallization. Directed crystallization methods produce composite materials based on Al, Md, Cu, Co, Tc Eutectic composite materials based on aluminum By the method of directional crystallization, the compositions Al-A^M and Al-CuAl1 are obtained. The composition is characterized by high structural stability up to melting temperatures. Nickel-based eutectic composite materials are heat-resistant materials used in rocket and space technology. Lamellar compositions containing a volume fraction of the hardening phase of more than 33-35% are brittle. Plastic compositions include nickel-based compositions with a volume fraction of fibers of 3-15% from tantalum, niobium, and hafnium carbides. Composite materials on a non-metallic basis. Cured epoxy, polyester, phenolic resins are used as a matrix. Composites reinforced with the same type of fibers are called by the reinforcing fiber. A composition containing a filler in the form of long glass fibers arranged in oriented individual strands is called oriented glass fiber. The filler of non-oriented fiberglass is a short fiber. If the reinforcing material is fiberglass, the material is called fiberglass. A composite material containing carbon fiber is called carbon fiber, boron fiber is called boron fiber, and organic fiber is called organo fiber. Advantages of composite materials with a polymer matrix: high specific strength and elastic characteristics; resistance to aggressive environments; good anti-friction and frictional properties along with high heat-shielding and shock-absorbing properties. 49. Chemical composition, methods for obtaining powders, properties and methods for their control Powder materials - materials obtained by pressing metal powders into products of the required shape and size and subsequent sintering of the molded products in a vacuum or protective atmosphere. Anti-friction powder alloys have a low coefficient of friction, are easy to machine, and have good wear resistance. Alloys based on non-ferrous materials are used in instrument making and electronic engineering. Powder materials are used in the manufacture of parts that have a simple symmetrical shape, small mass and size. Powder metallurgy is a branch of technology that deals with the production of metal powders and parts from them. Billets are pressed from metal powder, which are subjected to heat treatment - sintering. Metal powders are: iron, copper, nickel, chromium, cobalt, tungsten, molybdenum, titanium. There are two ways to obtain powders: mechanical and physico-chemical. The most common is the method of mechanical grinding of the feedstock (chips, scraps). Mechanical mills are used for grinding. Mechanical grinding has its drawbacks. These include the high cost of powders, which includes the cost of manufacturing the original cast metals and alloys, and the relatively low productivity of the process. Physico-chemical methods for obtaining powders: reduction of oxides, precipitation of metal powder from an aqueous salt solution. The production of powder is associated with a change in the chemical composition of the raw material. Physicochemical methods for obtaining powders are more versatile than mechanical ones. Due to the use of cheap raw materials, physicochemical methods are economical. The chemical composition of powders is determined by the content of the base metal or component and impurities. The physical properties of powders are determined by the size and shape of the particles, microhardness, density, and the creation of a crystal lattice. Technological properties are characterized by fluidity, compressibility and caking of the powder. Fluidity - the ability of a powder to fill a mold. Fluidity is of great importance in automatic pressing, where press performance is affected by mold filling speed. Low fluidity affects the inhomogeneity of the density of the workpieces. Compressibility refers to the ability of the powder to compact under the action of an external load and the adhesion strength of particles as a result of pressing. The compressibility of the powder is affected by the plasticity of the material of the particles, their size and shape. It increases with the introduction of surfactants into the composition of the powder. Structural materials that are used for the manufacture of blanks and finished parts are obtained using powder metallurgy methods. Composite materials with special physical, mechanical and performance properties are widely used in industry. Antifriction sintered materials are used for the manufacture of plain bearings. In antifriction materials, the solid component is the metal base, and the soft component is the pores filled with oil or plastic. Friction composite materials are complex compositions based on copper or iron. Graphite or lead helps to reduce the wear of the composition. Friction materials are used as bimetallic elements, consisting of a friction layer, which is sintered under pressure with the base (disk). Highly porous materials are used to make filters. Filters can be made of powders of corrosion-resistant steel, aluminum, titanium. Highly porous metal materials are produced by powder sintering without pre-pressing. To release gases during the sintering process, special substances are added to the powders. Metal-ceramic hard alloys have high hardness, heat resistance and wear resistance. They are used for the manufacture of cutting and drilling tools, and are also applied to the surface of wear parts. Powder metallurgy produces diamond-metal materials. Metal powders (copper, nickel) are used as a binder. Fibrous materials are widely used in modern technology of composite materials. To obtain them, wires made of tungsten, molybdenum, boron, graphite are used - depending on the required properties of the material being created. Fiber metallurgy is a branch of powder metallurgy that specializes in solving the issues of research and creation of fibrous materials. The mixture preparation process includes preliminary annealing, powder sorting by particle size (sieving) and mixing. 50. Forming and sintering of powders, fields of application Caking is the adhesion strength of particles as a result of heat treatment of pressed blanks. Prepared powders are mixed in ball and drum mills. Blanks from metal powders are formed by pressing (cold, hot, hydrostatic) and rolling. Depending on the size and complexity of the pressed blanks, one- and two-sided pressing is used. One-sided receive blanks of simple shape and blanks such as bushings. By double-sided pressing, the shaping of workpieces of complex shape is carried out. During hot pressing, the processes of shaping and sintering of the workpiece are technologically combined. As a result of hot pressing, materials are obtained that are characterized by high strength, density and uniformity of structure. Graphite is the best material for making molds. Hydrostatic pressing is used to obtain cermet blanks. As a working fluid, oil, water, glycerin are used. Extrusion produces bars, pipes and profiles of various sections. The profile of the manufactured part depends on the shape of the calibrated mold hole. Mechanical and hydraulic presses are used as equipment. Rolling is one of the most productive and promising methods used for the processing of powder materials. In some cases, the rolling process is combined with sintering and final processing of the resulting workpieces. Sintering is carried out in order to increase the strength of previously obtained workpieces by pressing or rolling. In pressed workpieces, individual particles have a small proportion of contact; therefore, sintering is accompanied by an increase in contacts between individual powder particles. Depending on the time and temperature of sintering, an increase in strength and density occurs as a result of activation of the process of formation of contact surfaces. If the technological parameters are exceeded, this can lead to a decrease in strength as a result of the growth of crystallization grains. Requirements are imposed on the sintering atmosphere - non-oxidizing conditions for heating billets. The blanks after the sintering process are subjected to additional processing in order to improve the physical and mechanical properties, obtain the final dimensions and shape, apply decorative coatings and protect the surface of the part from corrosion. To improve the physical and mechanical properties of sintered blanks, repeated pressing and sintering, impregnation with lubricants, thermal or chemical-thermal treatment are used. Repeated pressing and sintering results in higher density parts. Sintered materials can be forged, rolled, stamped at elevated temperatures. Pressure treatment reduces the porosity of materials and increases their plasticity. Powdered metal materials are sintered materials made using the powder batching, forming and sintering method. These materials include hard alloys, dispersion-strengthened composites, anti- and friction materials, powder steels, sintered non-ferrous metals, porous metal materials. In order to obtain sintered parts from powdered steel, mixtures of iron and alloy powders, as well as carbon and alloy steel powders, are used. Methods for obtaining powder steels: cold pressing and sintering; double pressing and sintering; hot pressing; hot stamping. Heat treatment of powder steels is carried out in special protective environments. In order to prevent the oxidation process, oil or water is used to cool the steels. Powder steels have one characteristic structural element - pores. The greater the porosity of the material, the lower the density, strength and toughness of the steel. However, many characteristics of materials do not depend monotonously on porosity. Thus, the crack resistance and impact strength of powdered iron varies nonmonotonically depending on the porosity. Powder sintered antifriction materials prepared using copper and steel dies are widely used in modern mechanical engineering. For the preparation of more durable and high-quality materials, special additives are used: calcium fluoride, graphite, turbostratic boron nitride. As a result, a porous structure is formed after the sintering process. The pore channels of this structure can retain oil particles and other liquid lubricants. Materials with a porous structure are the most suitable for replacing bronze and babbit metal anti-friction alloys, which are quite expensive to use. In powder metallurgy, mineral ceramics are produced, which are obtained using iron, cobalt and other refractory metals. Beryllium products are also manufactured by powder metallurgy. Manufacturing process: molding and sintering, hot plastic deformation. 51. Inorganic glasses. Technical ceramics Inorganic glass - chemically complex amorphous isotropic materials that have the properties of a brittle solid. The glasses are: 1. Glass formers - basis: a) Si02 - silicate glass, if Si02 > 99%, then it is quartz glass; b) AI2O3 + Si02 - aluminosilicate glass; c) B203 + Si02 - borosilicate glass; d) AI203 + B203 + Si02 - aluminoborosilicate glass; 2. Modifiers are introduced to give the glass certain properties. The introduction of oxides of alkaline earth metals (I, II group: Na, K) reduces the softening point. Oxides of chromium, iron, vanadium give the glass certain colors. Lead oxides increase the refractive index. Depending on the number of modifiers, glass can be: alkaline with modifiers up to 20-30%, alkali-free - up to 5% modifiers, quartz glass - no modifiers; 3. Compensators, suppress the negative impact of modifiers. Glasses in cars, fiberglass, optics, low thermal conductivity, insoluble in acids and alkalis. Glass properties: glasses are characterized by high hardness and tensile strength. Theoretically, the tensile strength reaches 10–12 GPa. Elastic modulus E = 70 GPa. Vickers hardness HV ~ 750 kgf/mm2. Practically, the tensile strength is 50-100 MPa. Low aB is explained by factors: high coefficient of linear expansion. As the glass cools, tensile stresses are formed on its surface, which leads to the appearance of cracks. Glass is a good thermal insulator, which also leads to cracking. Glass does not resist dynamic loads. Glass hardening methods: 1) pickling to remove the defective surface layer. The tensile strength increases to 3000 MPa. An inefficient method, since in the future the glass interacts with abrasive particles or solid materials; 2) creation of compressive stresses on the surface. To do this, hardening is carried out, heating is carried out to a certain temperature, then it is cooled in a given mode (heating temperature, cooling and holding time). The tensile strength increases to 1000-1500 MPa; 3) application of polymeric materials to the glass surface. The polymer binder glues microcracks on the glass surface. Quartz glass has a high gas permeability (helium, hydrogen, neon) compared to other silicate glasses, which, in addition to silicon dioxide, contain oxides of alkali and alkaline earth metals. There are two parameters that unite the structure of double phosphate glasses with the structure of double silicate glasses: the basic structural unit is tetrahedral element-oxygen groups; the addition of modifying oxides increases the number of non-bridging oxygen atoms. The hardening and melting of glass occurs gradually over a certain temperature range. Therefore, there is no specific solidification or melting point. In the process of cooling, the melt passes from a liquid to a plastic state, and after that - to a solid (glass transition process). Organic glasses are organic polymers - polyacrylates, polycarbonates, polystyrene, copolymers of vinyl chloride with methyl methacrylate, which are in a glassy state. Glasses based on polymethyl methacrylate have found the greatest practical application. According to their technology, hardening mechanism and structure, organic glasses differ from inorganic ones. Elementary glasses are capable of forming a small number of elements - sulfur, selenium, arsenic, phosphorus, carbon. Halide glasses are produced on the basis of the glass-forming component BeF2. Multicomponent compositions of fluoroberyllate glasses include aluminum, calcium, magnesium, strontium, and barium fluorides. Fluoroberyllate glasses are widely used in practice due to their high resistance to hard radiation, including X-rays, and aggressive media such as fluorine and hydrogen fluoride. Methods for obtaining glasses by vacuum evaporation, condensation from the vapor phase, and plasma spraying are gaining industrial importance. In these cases, glass can be obtained from the gas phase, bypassing the molten state. Ceramics - an inorganic material obtained by molding masses in the process of high-temperature firing. Oxide ceramics have high compressive strength compared to tensile or flexural strength. Fine-grained structures are more durable. With increasing temperature, the strength of ceramics decreases. Pure oxide ceramics are not subject to the oxidation process. Oxygen-free ceramics. The materials are very brittle. The resistance to oxidation at high temperatures of carbides and borides is 900-1000 °C, for nitrides it is lower. Silicides withstand temperatures of 1300-1700 °C. At such temperatures, a silica film forms on the surface. 52. Polymers, plastics Polymers are substances whose macromolecules consist of numerous repeating elementary units that represent the same group of atoms. The molecular weight of molecules ranges from 500 to 1000000. In polymer molecules, a main chain is distinguished, which is built from a large number of atoms. The side chains are shorter. Polymers whose main chain contains the same atoms are called homochain, and if the carbon atoms are carbon chain. Polymers containing different atoms in the main chain are called heterochain. Polymer macromolecules are classified according to their shape into linear, branched, flat, ribbon, spatial or reticular. Linear polymer macromolecules are long zigzag and twisted chains, which are inherently flexible, limited to rigid sections - segments consisting of several links. Such macromolecules have high strength along the main chain, are weakly interconnected and provide high elasticity of the material. Heating causes softening, and subsequent cooling causes the polymer (polyamide, polyethylene) to harden. A branched macromolecule contains side branches and this makes it difficult for macromolecules to approach each other and reduces intermolecular interaction. Polymers with this shape are characterized by reduced strength, increased fusibility and friability. Cross-linked forms of macromolecules are characteristic of more durable, insoluble, and infusible polymers that are prone to swelling in solvents and softening when heated. Polymer macromolecules are flexible. Plastics (plastics) are organic materials based on polymers that are able to soften when heated and under pressure to take a certain stable shape. Simple plastics are made up of chemical polymers alone. Complex plastics include additives: fillers, plasticizers, dyes, hardeners, catalysts. Fillers are introduced into plastics in an amount of 40-70% to increase hardness, strength, rigidity, and impart special specific properties. Fillers can be fabrics and powdery, fibrous substances. Plasticizers (stearin, oleic acid) help to increase elasticity, plasticity and facilitate the processing of plastics. Hardeners (amines) and catalysts (peroxide compounds) are added to plastics for curing. Dyes (mineral pigments, alcohol solutions of organic paints) give plastics a certain color and reduce their cost. The composition of the components, their combination and quantitative ratio allow you to change the properties of plastics over a wide range. Plastics are classified according to features. By type of filler: with solid filler; with gaseous filler. According to the reaction of the binder polymer to repeated heating. Thermoplastic plastics based on a thermoplastic polymer soften when heated and harden on subsequent cooling (pure polymers or polymer compositions with plasticizers, antioxidants). Thermoplastics are characterized by low shrinkage of 1-3%. They are characterized by low fragility, high elasticity and the ability to orientate. Thermosetting plastics based on thermosetting polymers (resins) after heat treatment - curing - go into a thermostable state and are brittle, have a large shrinkage of 10-15% and contain fillers in their composition. By application, they are divided into groups: structural - for power parts and structures, for non-power parts; gaskets, sealing; friction and antifriction; electrically insulating, radio-transparent heat-insulating; resistant to fire, oils, acids; facing and decorative. Polyethylene can be used for a long time at 60-100 °C. Frost resistance reaches -70 ° C and below. Chemically resistant and insoluble in solvents, it is used to insulate the protective sheaths of cables, wires, parts of high-frequency installations and the manufacture of corrosion-resistant parts - pipes, gaskets, hoses. It is produced in the form of a film, sheets, pipes, blocks. Polyethylene is subject to aging. Polystyrene is an amorphous, solid, transparent polymer that has a linear structure, high dielectric properties, satisfactory mechanical strength, low operating temperature (up to 100 °C), chemical resistance to alkalis, mineral and organic acids, oils. It swells in 65% nitric acid, glacial acetic acid, gasoline and kerosene. At temperatures above 200 °C, it decomposes to form styrene. Polystyrene is used for the production of lightly loaded parts and high-frequency insulators. Disadvantages - brittleness at low temperatures, a tendency to the gradual formation of surface cracks. Plastics are widely used in mechanical engineering and instrument making for the manufacture of parts. Plastics for electrical purposes are used as electrical insulating materials in machine structures. Author: Buslaeva E.M.
▪ Methods of teaching psychology. Lecture notes ▪ Fundamentals of life safety. Crib ▪ History of world and domestic culture. Lecture notes
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ section of the site Art video. Article selection ▪ article Garage lift. Tips for the home master ▪ article How many elementary particles are known now? Detailed answer ▪ article Maintenance of pressure vessels. Standard instruction on labor protection ▪ article Car pager with microphone. Encyclopedia of radio electronics and electrical engineering
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page