Ministry of Education of the Republic of Belarus
BELARUSIAN NATIONAL
TECHNICAL UNIVERSITY
Department of "Information-measuring equipment and technologies"
LABORATORY WORKS
(PRACTICE)
By discipline
"Materials Science and Technology of Materials"
Part 1
Minsk 2003 Introduction
In the process of studying the course "Materials Science and Technology of Materials", along with lectures and practical exercises, a laboratory practice plays an important role. Without mastering the skills of using the analysis of the behavior of materials under various conditions, it is impossible to synthesize new materials and to use them reasonably in practice.
Performing laboratory work will allow you to consolidate the theoretical provisions of the main sections of the science of materials, get acquainted with modern methods of scientific research and analyze the experimental results obtained. As a result, a small, fully completed scientific study can be performed.
The tutorial (part 1) contains laboratory work reflecting the study of the basic physical and chemical properties of structural materials and their structure.
A feature of the material presented is the presence of a fairly extensive theoretical part, which allows students to independently prepare for classes. The manual provides a list of additional literature, which will facilitate a more detailed study of the work.
The purpose of the manual is to familiarize with various metallic and non-metallic structural materials used in instrument making, and to acquire clear ideas about the diverse nature of physical and chemical phenomena that occur in materials under various conditions during their synthesis and operation.
After completing the laboratory work, a report is provided, which includes:
1) title page;
2) basic theoretical provisions;
3) the procedure for performing work with the presentation of results in the form of tables and graphical dependencies;
4) analysis of the results and conclusions. When carrying out laboratory work, it is necessary to strictly adhere to the safety requirements.
Laboratory work No. 1
STUDY OF THE STRUCTURE OF METALS AND THEIR ALLOYS
Objective: study the diagram of state "iron-carbon", get acquainted with the microstructure of iron-carbon alloys (steels and cast irons), powder composite materials.
Theoretical part
With a change in the concentration of components in alloys, as well as during their cooling or heating (under the condition of constant external pressure), significant phase and structural changes occur in these alloys, which can be clearly traced using charts states, which are a graphical representation of the state of the alloys. Diagrams are plotted for the equilibrium state of the alloys. Equilibrium condition- a stable state that does not change in time and is characterized by a minimum of the free energy of the system.
State diagrams are usually built experimentally. The thermal method is used to construct them. With its help, the cooling curves of the alloys are obtained. From the stops and inflections on these curves, due to the thermal effects of the transformations, the temperatures of the transformations themselves are determined. With the help of phase diagrams, the temperatures of melting and polymorphic transformations in alloys are determined, how many phases and which phases are present in an alloy of a given composition at a given temperature, as well as the quantitative ratio of these phases in the alloy. In addition to the thermal method, the study of the microstructure using optical and electron microscopes, X-ray diffraction analysis, the study of the physical properties of alloys, etc. are involved in the study of transformations in the solid state.
In binary alloys, the vertical is the temperature, and the horizontal is the concentration of the components. Each point on the abscissa axis corresponds to a certain content of one and the other component, taking into account the fact that the total content of the components at each point on this axis corresponds to 100%.
Therefore, as the amount of one component of the alloy increases, the content of the other component in the alloy must decrease.
The form of the phase diagram is determined by the nature of the interactions that take place between the components of the alloys in the liquid and solid states. It is assumed that there is unlimited solubility between the components in the liquid state, i.e. they form a homogeneous liquid solution (melt). In the solid state, components can form mechanical mixtures of pure components, unlimited solid solutions, limited solid solutions, stable chemical compounds, unstable chemical compounds, and also undergo polymorphic transformations.
Mechanical mixtures are formed if the elements that make up the alloy do not dissolve in each other and do not interact during solidification from a liquid state. In structure, the mixture is an inhomogeneous body. Crystallites of various components that form a mechanical mixture are visible on the thin section. Chemical analysis also identifies various components. Two types of crystal lattices are distinguishable.
Solid solutions- phases in which one of the components (solvent) retains its crystal lattice, and the atoms of other (dissolved) components are located in its lattice, distorting it. Chemical analysis of a solid solution shows the presence of two elements, and X-ray structural analysis shows one type of solvent lattice. The structure is homogeneous grains. If both components have the same crystal lattice, and their atomic diameters differ by no more than 8 - 15%, then unlimited solubility is possible (for example, gold and silver).
Chemical compounds are formed when the elements that make up the alloy interact with each other. In structure, they are homogeneous solids. The properties of chemical compounds differ from the properties of their constituent elements. They have a constant melting point. The crystal lattice of a chemical compound differs from the lattice of the initial components. In a chemical compound, a certain ratio of atoms of elements is preserved, i.e. there is a chemical formula of the compound.
State diagram of the "iron-carbon" system
Iron and its alloys with carbon
Polymorphism is the property of a substance or material to change its crystal lattice when the temperature changes, Crystalline forms of α-Fe and ... Carbon is a non-metallic element. In nature, it occurs in the form of two ... Under normal conditions, carbon is in the form of a graphite modification with a hexagonal layered lattice. Modification ...Become
Become- alloys of iron with carbon containing up to 2.14% carbon. In addition, the alloy usually contains manganese, silicon, sulfur and phosphorus. Some elements can be added specifically to improve the physicochemical properties (alloying elements).
By structure began to be divided into:
1) hypoeutectoid containing up to 0.8% carbon (composition P + F);
2) eutectoid steels containing 0.8% carbon (P);
3) hypereutectoid containing more than 0.8% carbon (P + sec. Ts).
Dot D - eutectoid point(When cooled, austenite forms a mechanical mixture of ferrite and cementite). Eutectoid transformation occurs not from a liquid, but from a solid solution.
Depending on the chemical composition, carbon and alloy steels are distinguished. In turn carbon steels may be:
1) low-carbon (carbon content less than 0.25%);
2) medium-carbon (carbon content is 0.25 - 0.60%);
3) high-carbon, in which the carbon concentration exceeds 0.60%.
Alloy steels subdivided into:
1) low-alloyed - the content of alloying elements is up to 2.5%;
2) medium-alloyed t - 2.5 up to 10% of alloying elements;
3) highly alloyed - contain over 10% alloying elements.
By appointment steel are:
1) structural, intended for tel and machine building products;
2) instrumental, from which cutting, measuring, stamping and other tools are made. These steels contain
more than 0.65% carbon;
3) with special physical properties, for example, with certain magnetic characteristics or a low coefficient of linear expansion (electrical steel, invar);
4) with special chemical properties, for example, stainless, heat-resistant or heat-resistant steels.
Depending on the content of harmful impurities(sulfur and phosphorus) steels are subdivided into:
1. Steels of ordinary quality, content up to 0.06% sulfur and
up to 0.07% phosphorus.
2. High-quality - up to 0.035% sulfur and phosphorus each separately.
3. High quality - up to 0.025% sulfur and phosphorus.
4. Especially high quality, up to 0.025% phosphorus and up to 0.0] 5% sulfur.
By the degree of oxygen removal made of steel, i.e. according to the degree of its deoxidation, they are distinguished:
1) calm steel, i.e. completely deoxidized, designated by the letters "cn" at the end of the brand;
2) boiling steels - weakly deoxidized, marked with the letters "kp";
3) semi-calm steels that occupy an intermediate position between the two previous ones; denoted by the letters "ps".
Depending on the standardized indicators (tensile strength σ, relative elongation δ%, yield strength δ t, cold bending), the steel of each group is divided into categories, which are designated by Arabic numerals.
Steel of ordinary quality denoted by the letters "St" and the conditional brand number (from 0 to 6), depending on the chemical composition and mechanical properties. The higher the carbon content and the strength properties of the steel, the higher its number. To indicate the category of steel, a number at the end corresponding to the category is added to the designation of the brand, the first category is usually not indicated.
For instance: St1kp2 - carbon steel of ordinary quality, boiling, grade No. 1, second category, supplied to consumers by mechanical properties (group A).
Quality steels marked as follows: at the beginning of the brand indicate the carbon content in hundredths of a percent for steels,
For instance: ST45 - high-quality carbon steel, calm, contains 0.45% C.
U7 - high-quality carbon tool steel containing 0.7% C, calm (all tool steels are well deoxidized).
The alloying elements that make up the steel are designated in Russian letters: A - nitrogen, K - cobalt, T - titanium, B - niobium, M - molybdenum, F - vanadium, V - tungsten, N - nickel, X - chromium, G - manganese, P - phosphorus, D - copper, C - silicon.
If after the letter designating the alloying element there is a number, then it indicates the content of this element in percent. If there is no figure, then the steel contains 0.8 - 1.5% of the alloying element.
For instance: 14G2 - low-alloy quality steel, calm, contains approximately 14% carbon and up to 2.0% manganese.
ОЗХ16Н15МЗБ - high-alloy high-quality steel, calm contains 0.03% C, 16.0% Cr, 15.0% Ni, up to 3.0% Mo, up to 1.0% Nb.
High quality and extra high quality steels they are marked in the same way as high-quality ones, but at the end of the grade of high-quality steel they put the letter A (this letter in the middle of the brand designation indicates the presence of nitrogen specially introduced into the steel), and after the especially high-quality grade - through a dash the letter "Ш".
For instance: U8A - carbon tool high-quality steel containing 0.8% carbon;
ЗОХГС-Ш is a particularly high-quality medium-alloy steel containing 0.30% carbon and from 0.8 to 1.5% chromium, manganese and silicon each.
Certain groups of steels are designated somewhat differently.
Ball bearing steels are marked with the letters "ШХ", after which the chromium content is indicated in tenths of a percent (ШХ6).
High-speed steels (complex alloyed) are designated by the letter "P", the following number indicates the percentage of tungsten in it (P18).
Automatic steels are designated by the letter "A" and a number indicating the average carbon content in hundredths of a percent (A12).
Cast iron
Cast iron called alloys of iron with carbon containing more than 2.14% carbon. They contain the same impurities as steel, but in greater quantities.
Cast irons, in contrast to steels, finish crystallization with the formation of a eutectic, have a low ability to plastic deformation and high casting properties.
Depending on the state of carbon in cast iron, there are:
1) cast iron, in which all carbon is in a bound state in the form of carbide (white cast iron);
2) cast iron, in which carbon is largely or completely in a free state in the form of graphite (gray, high-strength, malleable cast iron).
White cast iron does not contain graphite, all carbon is bound in cementite Fe 3 C. White cast irons, depending on the carbon content, are divided into:
1) hypereutectic - carbon content up to 4.3%. The structure consists of perlite, secondary cementite and ledeburite;
2) eutectic - carbon content 4.3%. The structure is composed of ledeburite;
3) hypereutectic - the carbon content is more than 4.3%. The structure is composed of ledeburite and primary cementite.
Dot C - eutectic... Eutectic transformation occurs from a liquid. The resulting eutectic is called ledeburite. At point C, three phases coexist simultaneously in equilibrium: liquid melt, austenite and cementite.
Gray cast irons contain carbon in a free state in the form of lamellar graphite. Under the microscope, the graphite will appear as dark, curved bands against a light background. Compared to the metal base, graphite has a low strength. The places of its occurrence can be considered as a discontinuity. Gray cast iron has poor mechanical properties in tensile tests. However, gray cast iron also has a number of advantages: it makes it possible to obtain cheap castings, and has good ones. machinability, high damping properties.
Gray cast iron is marked with two letters СЧ and two numbers corresponding to the minimum tensile strength in MPa.
For instance: SCh10 - gray cast iron with a tensile strength of 100MPa.
As the graphite inclusions are rounded, their negative role as cuts in the metal base decreases, and the mechanical properties of cast irons increase. The rounded shape of the graphite is achieved by modification. When magnesium is used as a modifier in an amount of up to 0.5%, ductile iron is obtained.
Ductile iron contains free carbon in the form of nodular graphite inclusions. Round dark grains of different sizes are observed under a microscope against a light background. Responsible parts are made from high-strength cast irons. High-strength cast iron is marked with the letters HF and a number characterizing the value of the ultimate resistance.
For instance: VCh 35 - high-strength cast iron with a tensile strength of 350 MPa.
Malleable cast iron contains carbon in a free state in the form of flaky graphite. Malleable cast iron is obtained from white cast iron by graphitizing annealing (long-term annealing at a temperature of 1000 ° C). Under the microscope, a flocculent phase is observed against a light background.
Malleable cast iron is marked with the letters KCH and two numbers: the first is the tensile strength, the second is the relative elongation.
For instance: KCH 35-10 - malleable cast iron with a tensile strength of 350 MPa and a relative elongation of 10%.
The microstructure of cast iron consists of a metal base and graphite inclusions. The properties of cast iron depend on the properties of the metal base and the nature of the graphite inclusions.
The metal base can be:
1) pearlite (dark base under a microscope);
2) ferrite-pearlite (alternation of light and dark areas under a microscope);
3) ferritic (light base under a microscope).
The structure of the metal base determines the hardness of the cast iron.
Graphitization the process of graphite release during crystallization or cooling of iron-carbon alloys is called. Graphitization is a diffusion process and is slow. The graphitization process consists of several stages:
1) the formation of centers, graphitization;
2) diffusion of carbon atoms to the centers of graphitization;
3) growth of graphite precipitates.
Composite materials obtained by the method
Powder metallurgy
The technological process of manufacturing products from powders includes: obtaining powders, preparing a charge, molding, sintering, hot ... When forming blanks from powders of a certain chemical composition ...Study of the structure of alloys
The study of the structure of alloys in this work is carried out using an optical microscope. The image is formed in reflected light. For microanalysis, samples with a polished surface are made - ... As a result of the analysis, the shape of the inclusions, their size, distribution, the amount of graphite, alloying elements, ...experimental part
1. Using samples-microsections of powder materials, examine and graphically depict the structure of materials under a microscope. Compare the structure with the description in the album.
2. Using samples-microsections of steels and an auxiliary album with photographs, study and graphically depict their structure. Determine the carbon content in the samples and the phase composition according to the phase diagram given in the theoretical part.
3. Using samples-microsections of cast iron and an auxiliary album with photographs, study and graphically depict their structure. Determine the type of cast iron, the shape of the graphite inclusions, the type of metal base. Determine the carbon content in white cast irons. Determine the phase composition of white cast irons from the state diagram.
4. Examine the iron-carbon state diagram. Identify lines of liquidus, solidus, eutectoid and eutectic points, lines of phase transitions, melting points of iron, cementite, etc.
5. Based on the results of the work carried out, formulate conclusions.
Laboratory work No. 2,
STUDY OF MECHANICAL PROPERTIES
CONSTRUCTION MATERIALS
Objective: study the mechanical properties of structural materials and methods for assessing properties.
Theoretical part
The mechanical properties of materials depend on the type of stress state (created in the samples during testing), the conditions and nature of loading, speed, temperature and the state of the external environment. The purpose of mechanical testing of materials is to determine precisely these or those properties or their combination, which will most fully characterize the reliability of the corresponding products in the given service conditions. The combination of these mechanical properties can be called structural strength.
Various combinations of mechanical properties are taken as evaluation criteria. The following groups of criteria are distinguished:
1. Estimates of the strength properties of materials, determined often and regardless of the characteristics of the products made from them and the conditions of their service. Typically, these strength properties are determined under tensile conditions under static loading.
2. Assessments of the properties of materials directly related to the service conditions of products, and determining their durability and reliability.
3. Estimates of the strength of the structure as a whole, determined during bench and operational tests.
The first two groups of criteria for evaluating properties are determined on samples, then
as the latter - on finished parts and structures.
The main mechanical properties of materials include:
1) strength- the ability of the material to resist destruction under load;
2) plastic- the ability of the material to irreversibly change its shape and size without destruction under the action of a load;
3) fragility- the ability of the material to break down without protective energy absorption;
4) viscosity- the ability of the material to irreversibly absorb mechanical energy until the moment of destruction;
5) elasticity- the ability of the material to restore its shape and size after removing the load;
6) hardness- the ability of a material to resist the penetration of another body into it in the surface layer.
Stretch diagram
Plotting the tensile diagram is the main task of tensile testing. For these tests, cylindrical samples from ... The OA zone is called the elastic zone (after removing the load Ppc, the sample ...Determination of the hardness of materials
Hardness- the ability of the material to resist deformation in the surface layer under local contact effects.
Advantages of Hardness Measurement
2. Measurement of hardness according to the technique of execution is much easier than determination of strength (does not require special samples, performed ... 3. Measurement of hardness does not entail destruction of the checked part and ... 4. Hardness can be measured on parts of small thickness, as well as in thin layers.Determination of hardness according to the Mohs scale
with glass, knife blade, etc., as shown in table. 2.1. Table 2.1experimental part
1. Tensile tests.
1.1. Prepare tensile cylindrical steel specimens.
1.2. Carry out the necessary measurements of the lengths and diameters of the samples using a caliper. Enter the data in table 2.2.
Table 2.2
1.3. Determine the main mechanical characteristics, namely the ultimate strength of the material, relative elongation and relative contraction according to the formulas given in the theoretical part of the work.
1.4. Build a diagram of tension of steel images in coordinates Р-Δl.
1.5. Get acquainted with the tensile diagrams of various structural materials issued by the teacher, highlight the main zones, and determine the mechanical characteristics.
2. Determination of the hardness of materials.
2.1. Determination of Brinell hardness:
a) the test piece is placed on the table of the hardness tester;
b) set the value of the loading force and the duration of the load;
c) make an imprint on the sample, lower the instrument stage, remove the sample;
d) using a microscope, measure the diameter of the resulting print and calculate the Brinell hardness.
2.2. Determination of Vickers hardness:
a) determine the length of the diagonals of the imprint on the sample mounted on the stage of the microscope;
2.3. Study of the influence of the carbon content in steel on its hardness;
a) measure the diameters of the indentations of the samples obtained for steels ST20, ST45, U8;
b) determine the Brinell hardness values using the reference tables;
c) build a graphical dependence of hardness on carbon content and explain it.
3. Based on the results of the work, formulate conclusions.
Laboratory work No. 3
STUDY OF THE PROCESS OF CRYSTALLIZATION OF MATERIALS
Objective: to study the features of the crystallization process of materials using the example of salts and metals, to determine * the influence of various factors on the structure of the crystallized material, to get acquainted with the method of thermal analysis.
Theoretical part
Any substance can be in one of three states of aggregation: solid, liquid and gaseous. The transition from one state to another occurs at a certain temperature, called the melting, crystallization, boiling or sublimation temperature.
Crystalline solids have a regular structure, in which atoms and ions are located in the nodes of crystal lattices (the so-called short-range order), and individual cells and blocks are oriented in a certain way with respect to each other (long-range order). In liquids, a certain orientation does not apply to the entire volume, but only to a small number of atoms that form relatively stable groups, or fluctuations (short-range order). With decreasing temperature, the stability of fluctuations increases, and they show the ability to grow.
As the temperature of the solid increases, the mobility of atoms in the lattice sites increases, the vibration amplitude increases and upon reaching
at a certain temperature, called the melting point, the lattice collapses to form a liquid phase.
The opposite picture is observed when the liquid (melt) is cooled and then solidified. Upon cooling, the mobility of atoms decreases, and near the melting point, groups of atoms are formed, in which the atoms are packed, as in crystals. These groups are centers of crystallization or nuclei, on which a layer of crystals subsequently grows. Upon reaching the "melting-solidification" temperature, a crystal lattice is formed again, and the metal goes into a solid state. The transition of a metal from a liquid to a solid state at a certain temperature is called crystallization.
Crystalline bodies are characterized by anisotropy- dependence of properties on direction. Amorphous bodies (e.g. glass) are isotropic- their properties do not depend on the direction.
Consider the thermodynamic conditions of crystallization. The energy state of any system is characterized by a certain supply of internal energy, which is made up of the energy of the movement of molecules, atoms, etc. Free energy is a component of internal energy that can be converted into work under isothermal conditions. The amount of free energy changes with temperature changes, melting, polymorphic transformations, etc.
According to the second law of thermodynamics, any system tends to the minimum value of free energy. Any spontaneously running process occurs only if the new state is more stable, i.e. has a smaller supply of free energy. For example, a ball tends to roll down an inclined plane, while lowering its free energy. Spontaneous return of the ball up the inclined plane is impossible, since this will increase its free energy.
The crystallization process obeys the same law. A metal solidifies if the solid state has less free energy, and melts when the liquid state has less free energy. The change in the free energy of the liquid and solid state with a change in temperature is shown in Fig. 3.1. Temperature changes in free energy are different for the liquid and solid states of matter.
Rice. 3.1. Thermodynamic crystallization condition
Distinguish between theoretical and actual crystallization temperature.
T 0 - theoretical, or equilibrium crystallization temperature at which F w = F tv At this temperature, the existence of a metal in both liquid and solid states is equally probable. Real crystallization will begin when this process is thermodynamically beneficial to the system, provided that ΔF = F w - F tv, which requires some overcooling. The temperature at which crystallization practically takes place is called actual crystallization temperature T cr. The difference between theoretical and actual, crystallization temperatures is called degree of hypothermia: ΔТ = Т 0 - Т cr. The greater the degree of supercooling ΔТ, the greater the difference in free energies ΔF, the more intense crystallization will take place.
Just as solidification requires supercooling to the actual crystallization temperature, melting requires superheating to achieve the actual melting point.
Mechanism of the crystallization process
1) nucleation of crystallization centers; 2) the growth of crystals from these centers. At temperatures close to the solidification temperature, small groups of atoms are formed in the liquid metal, so ...Thermal analysis
Rice. 3.5. Types of cooling curves When a pure element crystallizes, the removal of heat due to cooling is compensated for by heat ...Calm steel ingot structure
A diagram of the structure of a calm steel ingot is shown in Fig. 3.7. The ingot structure consists of three zones: outer fine-grained zone 1, columnar zone ... Fig. 3.7. Metal ingot structureexperimental part
1. Conduct thermal analysis of the metal.
1.1. Switch on the oven in which the metal sample is placed.
1.2. Heat (melt) the sample to the temperature specified by the laboratory assistant.
1.3. Take readings of the measuring device every 60 seconds. The readings are translated using a calibration table.
1.4. When the final temperature of the experiment is reached, turn off the furnace and carry out the process of cooling (crystallization) of the metal.
1.5. Take readings of the measuring device every 60 seconds.
1.6. Plot heating and cooling curves in coordinates
"Temperature - time" on one graph.
1.7. Determine the critical points of aggregate transformations and
hypothermia degree.
2. To study the crystallization process by the example of metal salts.
2.1. Apply drops of saturated salt solutions on a glass slide and place on the microscope stage.
2.2. Consider and graphically depict the structures of salts obtained after a certain period of time in the process of natural evaporation of water. Determine the types of crystalline formations, the sequence of the formation of zones, their number.
3. Based on the experimental results, formulate conclusions.
Laboratory work No. 4
STUDY OF THERMAL PROPERTIES
CONSTRUCTION MATERIALS
Target work: to study the thermophysical properties of materials. Determine the temperature coefficient of linear expansion of the alloy.
Theoretical part
For a number of branches of instrumentation, it is necessary to use materials with strictly regulated thermal properties. The main thermophysical properties include: heat resistance, cold resistance, thermal conductivity, heat resistance, heat capacity, and thermal expansion.
Heat resistance refers to the ability of materials, without damage and without an acceptable deterioration of other practically important properties, to reliably withstand the action of elevated temperatures (for a short time or for a time that is comparable to the normal operating time). The magnitude of the heat resistance is assessed by the corresponding values of the temperature at which the changes in properties appeared (for example, electrical for inorganic dielectrics). The heat resistance of organic dielectrics is often determined by the onset of mechanical deformation. If the deterioration of properties is detected only after prolonged exposure to elevated temperatures - due to slow chemical processes, then this is the so-called heat aging of the material... In addition to the effect of temperature, an increase in air pressure, oxygen concentration,
various chemical reagents, etc.
For a number of fragile materials (glass, ceramics), resistance to sudden changes in temperature - thermal impulses - is important. The ability to withstand heat cycles is called heat resistance. With rapid heating or cooling of the material surface, due to the creation of a temperature difference between the outer and inner layers of the material and uneven thermal expansion or contraction, cracks can form. Heat resistance is assessed by the number of thermal cycles that a material sample has withstood without a noticeable change in properties.
As a result of tests, the resistance of the material to thermal influences is determined, and this resistance in different cases may not be the same. For example, a material that can easily withstand short-term heating to a certain temperature may turn out to be unstable with respect to thermal aging when exposed to even lower temperatures for a long time, or a material that can withstand prolonged heating to a high constant temperature cracks upon rapid cooling and changes its properties. An elevated temperature test sometimes needs to be performed with a simultaneous exposure to high air humidity (tropical climate).
When the equipment is designed to operate at low temperatures, its cold resistance is important - the ability of the material, without damage and without unacceptable deterioration of other practically important properties, to reliably withstand exposure to low temperatures, for example, from -60 ° C and below. At low temperatures, as a rule, the electrical properties of insulating materials improve, however, many materials, which are flexible and elastic at ordinary temperatures, become very fragile and tough at low temperatures, which leads to unreliable operation.
All solids are capable of conducting heat to one degree or another. Some are worse, others are better. Thermal conductivity is the property of materials to conduct heat from warmer parts of the body to less heated ones, leading to temperature equalization.
In principle, there are the following methods of transferring thermal energy in a substance:
1) radiation- all bodies, whatever their temperature, radiate energy. It can be a purely thermal phenomenon (heat radiation) and
luminescence (phosphorescence and fluorescence), which is of non-thermal origin;
2) convection- direct heat transfer associated with the movement of liquids and gases;
3) thermal conductivity- heat transfer due to the interaction of atoms or molecules of a substance. In solids, the transfer of thermal energy is carried out mainly by this method.
The basic law of thermal conductivity Fourier states that the heat flux density is proportional to the temperature gradient. The law is valid for isotropic bodies (properties do not depend on direction). Anisotropic solids are characterized by thermal conductivity coefficients in the direction of the principal axes.
In the general case, thermal conductivity in solids is carried out by two mechanisms - the movement of current carriers (electrons, mainly) and elastic thermal vibrations of lattice atoms. Aluminum, gold, copper, silver have the maximum coefficient of thermal conductivity. Crystals with a more complex lattice structure have a lower thermal conductivity, because the degree of dissipation of thermal elastic waves is greater there. A decrease in thermal conductivity is also observed during the formation of solid solutions, since in this case, additional centers for the scattering of heat waves arise. In heterophase (multiphase) alloys, the thermal conductivity is the sum of the thermal conductivities of the resulting phases. The thermal conductivity of the compounds is always significantly lower than the thermal conductivity of the components that form them.
Heat capacity- this is a property of the substance itself, it does not depend on the structural features of a particular product, its porosity and density, crystal size and other factors. Heat capacity is the amount of heat corresponding to a change in the temperature of a unit of the amount of a substance by 1 ° C.
Thermal expansion- an increase in the volume and linear dimensions of bodies with a change in temperature. It is characteristic of almost all materials.
Although the strength of the binding forces in a solid is very high, there are possibilities for the movement of elementary particles (atoms, ions). In both amorphous and crystalline bodies, atoms vibrate near the center of equilibrium.
In this case, the amplitude of oscillations increases with increasing temperature. Practice shows that the specific volume of most substances also increases with increasing temperature, i.e. thermal expansion takes place. The phenomenon of thermal expansion, however, is associated not with an increase in the amplitude of the vibrational motion of atoms, but with its anharmonicity. To understand the essence of the phenomenon, it is necessary to consider the force interaction during the formation of a chemical bond between atoms, as well as the dependence of the potential energy of the system on the interatomic distance. Any kind of chemical bond involves a balance of attractive and repulsive forces between atoms. When atoms approach each other, the forces of attraction initially dominate. The approach of atoms to a certain limit reduces the energy of the system, i.e. provides her with greater stability. At a sufficiently small interatomic distance, however, repulsive forces appear, which prevent the further approach of the atoms. The action of these forces increases with decreasing interatomic distance, which corresponds to an increase in the energy of the system. At a certain value of the interatomic distance, the forces of repulsion and attraction will balance, after which further approach requires the application of an external force, which corresponds to positive values of the resulting force F res.
Rice. 4.1. Power interaction diagram between
oppositely charged particles
The potential pit is characterized by strongly pronounced asymmetry. Suppose, at a certain temperature, the vibrating atom has a certain energy. In this case, he oscillates about the center, deviating alternately "left and right". Since the offsets from the position
equilibrium must be the same, then an increase in the energy of the system causes a shift in the center of vibrations along the axis of the interatomic distance. Thus, the average distance between atoms increases with increasing temperature, which corresponds to the thermal expansion of the body.
Thus, the phenomenon of thermal expansion of solids is based on the anharmonicity of the vibrational motion of its atoms, and the degree of deviation of thermal vibrations from the harmonic law, i.e. the amount of thermal expansion of the body is largely determined by the degree of asymmetry of the potential well. As a rule, in substances with an ionic bond, the potential well is characterized by significant width and asymmetry. This fact determines a significant increase in the average interatomic distances upon heating, or a significant thermal expansion of ionic compounds.
On the contrary, in substances with a predominantly covalent bond (borides, nitrides, carbides), the potential well has the shape of a sharpened depression, and therefore the degree of its symmetry is higher. Therefore, the increase in the distance between atoms upon heating is relatively small, which corresponds to their relatively small thermal expansion. Metals usually exhibit increased thermal expansion, because the metallic bond is generally weaker than the ionic and covalent bonds. Finally, organic polymers are characterized by very large expansion on heating due to weak van der Waals forces acting between molecules, while powerful covalent forces act inside the molecules.
Quantitatively, the thermal expansion of materials is estimated by the following values:
1. The temperature coefficient of linear expansion at a given temperature (TCLE), corresponding to the relative elongation of the sample at an infinitesimal change in temperature.
2. The temperature coefficient of volumetric expansion, which characterizes the three-dimensional expansion of a substance.
An important practical consequence is the need to use the LTEC data obtained in a specific temperature range in which the material operates. Temperature coefficients cannot be compared
expansions of materials measured at various temperatures.
For isotropic materials (crystals with a cubic lattice, glasses), the TCLE is the same in all directions. Most crystalline substances, however, are anisotropic (expansion is different along different axes). This phenomenon is most pronounced, for example, in layered materials (graphite), when chemical bonds have a pronounced directionality. As a result, graphite has much less expansion along the layer than perpendicular to it. For some similar materials with strongly pronounced anisotropy, the LTEC in one direction may even turn out to be negative. For example, cordierite 2MgO 2A1 2 O 3 5SiO 2, in which, upon thermal expansion, expansion of the crystal is observed along one axis, and compression along the other axis, corresponding to the approach of the layers of the structure. This phenomenon is used in technology; in a field and crystalline material, the chaotic distribution of crystals leads to the mutual orientation of their positive and negative expansion. As a result, a material with a low LTEC value is obtained, which is characterized by very high thermal stability. At the same time, significant stresses can arise in such materials at the grain boundaries, which is reflected in their mechanical strength. For polyphase materials, at the interface of two contacting phases with different LTEC, the phase with a large coefficient of expansion will be affected by compressive stresses and tensile stresses will act on the phase with a low LTEC (during heating). On cooling, the voltages change signs. If the critical stress values are exceeded, cracks and even material destruction are possible.
Thus, LTEC is a structurally sensitive property and is sensitive to changes in the structure of a material, for example, to the presence of polymorphic transformations in it. In this regard, bends can be observed on the expansion curves of multiphase materials, and their monotonic character is violated.
If the expansion of the body in a given temperature interval occurs uniformly, then graphically the expansion will be expressed by a straight line (Fig. 4.2.), And the average coefficient of linear expansion will be numerically equal to the tangent of the angle of inclination of this straight line to the temperature axis, referred to the relative change in the length of the sample.
Rice. 4.2. Uniform expansion of the body when heated
However, the expansion of the sample is not always uniform. The study of the features of thermal expansion in different temperature ranges also makes it possible to draw indirect conclusions about the temperature and the nature of various structural transformations in the material. In such cases, the dependence of thermal expansion on temperature will be expressed not by a straight line, but by a more complex dependence (Fig. 4.3).
Rice. 4.3. Uneven expansion of the body when heated
To find the value of the expansion coefficient at individual points of the expansion curve, you need to draw a tangent to the temperature axis through the point of the curve corresponding to the measurement temperature. The value of the coefficient of linear expansion will be expressed by the tangent of the angle of inclination of the tangent to the temperature axis.
The amount of thermal expansion of bodies upon heating primarily depends on the nature of the given material, i.e. from its chemical and mineralogical composition, the structure of the spatial lattice, the strength of the chemical bond, etc. So,
The LTEC value of ceramics is determined, first of all, by the nature of the crystalline phase, glass - by the chemical composition, and sitall - by the nature of the crystalline phase, the chemical composition of the residual glassy phase and their ratio.
Glassy materials give a complex temperature dependence of expansion. Initially, up to the so-called glass transition temperature, close to the softening point, the expansion proceeds in proportion to the temperature. At temperatures above the glass transition temperature, the elongation rate increases sharply. This section corresponds to the transition interval from the brittle to the high-viscosity state, in which the processes of structural rearrangement of glass take place, and the glass transition temperature is considered to be the boundary of the brittle state. After reaching the maximum, the elongation begins to decrease, which is associated with the shrinkage of the glass sample as a result of its softening.
TCLE is a technical characteristic of a material and is calculated by the formula
where l 0 - body length at an initial temperature T 0;
l t is the length of a body heated to a temperature T.
LTEC is the change in length when the temperature changes by 1 degree, referred to the original length of the sample. Materials with low TLEC are used as parts of high-precision instruments and equipment, which should not change their dimensions when heated. When the parts of the device are rigidly connected, for example, in a metal-to-glass junction, it is necessary to select materials with close LTEC values, otherwise, during cooling, stresses will arise at the junction of the parts, and cracks may form in fragile glass, and the junction will not be vacuum-tight. The proximity of the TCLE is also necessary for the layers of microcircuits that undergo temperature changes during technological operations or during operation, otherwise the destruction of the circuit layers may occur.
The coefficient of thermal expansion also plays an important role in assessing the thermal stability of materials: the lower the TCLE, the higher the thermal shock resistance.
There are metal alloys that do not obey the general laws of thermal properties. Such alloys are Fe-M1 iron-nickel alloys. The alloy containing 36% nickel has a TEC value close to zero and is called invar(lat. "unchanged").
Engineers take advantage of another thermal property, namely thermal coefficient of elastic modulus(TCMU). In any solids, including metals, when heated, there is a decrease in the elastic modulus, which is a measure of the forces of interatomic bonds. For the Fe-N alloy, this property has an anomalous dependence: the TCMU modulus increases or remains constant with increasing temperature. The same Invar with 36% nickel has the highest TCMU. The selection of a certain chemical composition makes it possible to develop alloys, the TCMU of which is practically independent of temperature. These alloys are called elinwaram.
Steels with a certain thermal expansion are used for the manufacture of thermobimetals when a layer with low thermal expansion (passive layer) is rolled securely with another layer with higher thermal expansion (active layer). Bimetallic plates are used as a thermostat in instrument making.
Heating such a plate leads to its curvature, which makes it possible to close the electrical circuit. The main property of thermobimetals is thermal sensitivity- the ability to bend when the temperature changes.
Description of the quartz dilatometer used to measure the thermal coefficient of linear expansion
The other end of the rod is connected to the rod of the indicator head. The indicator head is mounted on a metal stand. Tight contact of the rod with the sample is carried out using the pressure of the indicator spring. When expanding, the sample presses through ...experimental part
1. Become familiar with the dilatometer device.
2. Place the tube with the bronze sample in the tube furnace.
3. Switch on the oven and combination reading instrument.
4. Set the indicator to zero.
5. At regular intervals (for example, after 20 ° С), take the indicator readings using the calibration table.
6. Enter the experimental data in the table. 4.2.
where α is the coefficient of linear expansion;
n- indicator readings;
k- indicator division price;
(T 2 - T 1) - temperature difference (room and final) for the selected interval;
l- initial length of the sample;
α sq - correction for the expansion of quartz.
8. Construct and explain the graphical dependence of the specimen elongation on temperature.
9. Analyze the results obtained for bronze, which is an alloy of copper and tin, taking into account that α copper = 160 · 10 -7 gr -1, α tin = 230 · 10 -7 gr -1.
10. Get acquainted with the expansion curves for non-metallic materials, highlight characteristic zones, explain the processes occurring in materials when heated.
11. Based on the results of the work, formulate conclusions.
Laboratory work No. 5
METHODS FOR STUDYING POROUS COMPOSITE MATERIALS
Objective: get acquainted with various porous materials and their manufacturing technology. Determine the water absorption of polymer, composite and glass-ceramic materials and make a comparative analysis of the results.
Theoretical part
All materials have more or less water absorption, i.e. ability to absorb v moisture from the environment and moisture permeability, those. the ability to let water through. Atmospheric air always contains some water vapor.
The water absorption of a material is significantly influenced by its structure and chemical nature. An important role is played by the presence and size of capillary gaps inside the material, into which moisture penetrates. Highly porous materials, in particular fibrous ones, have high water absorption. Determination of water absorption by increasing the mass of a wetted sample gives some idea of the material's ability to absorb moisture.
Any porous structural material (metal, ceramic, glass-ceramic or polymer) is, as a rule, a combination of a solid with voids - pores. The volume of pores, their sizes and the nature of distribution have a significant impact on a number of properties of products and materials. So, for example, the mechanical strength of ceramics depends not only on the total porosity, but also on the size of the pores, the uniformity of their distribution. Undoubtedly, with an increase in porosity, the strength of ceramics decreases due to an increase in the defectiveness of the structure and a decrease in the strength of bonds.
It has been established that the volume of pores filled with water determines the frost resistance of products; the number, size and distribution of pores largely determine the slag resistance of the furnace lining; porosity affects the thermal conductivity of materials.
The pores in the materials have various shapes, outlines, can be unevenly distributed over the volume, therefore full description porosity is extremely difficult to obtain, even with the use of modern porosimeters. Despite the variety of shapes, pores can be divided into:
1. Closed pores- liquids and gases inaccessible for penetration into them.
2. Open- pores available for penetration.
Open pores, in turn, are divided into:
1) dead-end- pores filled with liquid and gas, open on one side;
2) channel-forming- pores open at both ends, creating pore channels.
The moisture permeability of the material is primarily determined by the channel-forming pores in the presence of pressure drops at their open ends. Porosity and permeability are important texture characteristics for all types of technical materials.
Since direct methods of measuring the porosity of materials are extremely complex, this indicator is often assessed by determining other properties that directly depend on porosity. These indicators include material density and water absorption.
Let's get acquainted with some definitions.
True density- the ratio of the mass of the material to its volume, excluding pores.
Apparent density is the ratio of body weight to the entire volume occupied by it, including pores.
Relative density is the ratio of apparent density to true density. It represents the volume fraction of solids in the material.
Water absorption is the ratio of the mass of water absorbed by the material at full saturation to the mass of the dry sample (expressed as a percentage).
By measuring the above characteristics, the total, open and closed porosity of the ceramic can be estimated.
True (total) porosity- the total volume of all pores open and closed, expressed in% to the total volume of the material. This value is denoted by P and and is numerically equal to the sum of closed and open porosity.
Apparent (open) porosity is the ratio of the volume of all open pores of the body (filled with water during boiling) to the entire volume of the material, including the volume of all pores. The value is designated P 0 and is expressed in%.
Closed porosity- this is the ratio of the volume of all closed pores of the body to its volume, including the volume of all pores, denote it through P 3 and expressed in%.
Water absorption of polymeric materials
At low temperatures and a short time of contact of water with the polymer, swelling is limited and extends to a small ... In composite materials, which are plastics, water resistance ... Plastics are non-metallic materials based on natural or synthetic high-molecular compounds ...Classification of plastics
Plastics can be classified according to various criteria, such as composition, heat and solvent resistance, etc.
By composition plastics are divided into:
1) unfilled. They are pure resin.
2) filled (compositional). Contain, in addition to resins, fillers, plasticizers, stabilizers, hardeners and special additives.
Excipients added in an amount of 40-70% (by weight) to improve mechanical properties, reduce shrinkage and reduce the cost of the material (the cost of the filler is lower than the cost of the resin). However, the filler increases the hygroscopicity of the plastics and degrades the electrical performance.
Plasticizers(glycerin, castor or paraffin oil) is added in an amount of 10-20% to reduce fragility and improve the formability of the awn.
Stabilizers(carbon black, sulfur compounds, phenols) are added in an amount of several percent to slow down aging, which stabilizes the properties and lengthens the service life. Aging is a spontaneous irreversible change in the most important performance characteristics of a material during operation and storage, which occurs as a result of complex physical and chemical processes.
Hardeners they are also introduced in an amount of several percent for the connection of polymer molecules by chemical bonds.
Special additives- lubricants, colorants, to reduce static charges, to reduce flammability, to protect against mold.
In the manufacture of porous and foam plastics, blowing agents are added - substances that soften when heated, releasing a large amount of gases that foaming the resin.
In relation to heating and solvent plastics are divided into thermoplastic and thermosetting.
Thermoplastic polymers(thermoplastics) - polymers that can soften many times when heated and harden when cooled without changing their properties. In these polymers, weak van der Waals forces act between molecules, and there are no chemical bonds. Thermoplastics are also soluble in solvents.
Thermosetting polymers(thermosets) when heated to a certain temperature melt and, as a result of chemical reactions at the same temperature, when cooled, they solidify (as they say, "baked"), turning into a hard, non-melting and insoluble substance. In this case, along with weak van der Waals forces, strong chemical bonds between molecules, called transverse, act. Their occurrence is the essence of the polymer curing process.
By the decreasing influence of the filler plastics are divided into the following types:
1) with sheet filler (getinax, textolite, fiberglass, wood-laminated plastic);
2) with fiber filler(fiberglass, asbestos fiber, fiberglass);
3) powder-filled(phenolic, aminoplasts,
epoxy press powders);
4) without filler(polyethylene, polystyrene);
5) with gas-air filling(foams).
Getinax consists of two or more layers of strong, heat-resistant, impregnating paper treated with a thermosetting phenol-formaldehyde resin of the resol type (Bakelite). In order to increase the heat resistance, organosilicon substances are additionally introduced into some brands of Getinax, and epoxy resins are added to increase the adhesive ability. Getinax is a cheap material used in CEA for the manufacture of various types of flat electrical insulating parts and bases of printed circuit boards.
Heat resistance of getinax - 135 ° С. Disadvantages: ease of delamination along the filler sheets, hygroscopicity (this worsens the electrical insulating properties). To protect against moisture, the surface is varnished.
Textolite is a pressed material based on sheets of cotton fabric, impregnated, like getinax, with bakelite. It is easier to process than getinax and has higher water resistance, compressive strength and impact strength. Textolite is 5-6 times more expensive than getinax. Heat resistance 150 ° С.
Glass fiber laminate- a material consisting of two or more layers of alkali-free glass cloth impregnated with various thermosetting resins.
Glass fiber laminate, in comparison with getinax and textolite, has increased moisture resistance, heat resistance and better electrical and mechanical parameters, but it is less processed mechanically. Glass fiber laminate has good damping ability (vibration damping ability) and surpasses steel, titanium alloys in this respect. In terms of thermal expansion, it is close to steels. Heat resistance - 185 ° С. Glass fiber laminate is widely used, since it combines light weight, high strength, heat resistance and good electrical properties.
Laminate is a material filled with sawdust or veneer.
Sheet foil plastics have a special purpose and are used for the manufacture of printed circuit boards. They are laminated plastics lined with electrolytic copper foil on one or both sides.
This method of foil production provides a homogeneous composition and a rough surface on one side, which improves the adhesion of the foil to the dielectric when glued. Composite plastics filled with cotton fibers and fabrics, as well as based on wood materials, can have high water absorption due to the filler. According to GOST 4650-73, the water absorption of polymeric materials is determined when the sample is in water for 24 hours at room temperature (or when boiling for 30 minutes).
Table 5.1.
Properties of plastics
2. Plastics are resistant to the long-term action of industrial corrosive environments and are used for the manufacture of protective coatings for metals. ... 3. Under the influence of the environment, plastics age slowly, that is ... 4. Most polymers can only work for a long time at temperatures below 100 ° C. Above this temperature, like ...Porous ceramic and glass-ceramic materials
1) preparation of initial powders, 2) consolidation of powders, i.e. production of compact materials; 3) processing and control of products.Porous metallic materials
Highly porous powder metal materials, due to the rigid spatial frame, have a higher strength. They withstand ... The manufacturing technology of metal porous elements depends on the shape and ...experimental part
1. Determine the water absorption of polymeric materials.
1.1. Weigh samples of polymeric materials before testing (mass m 1).
1.2. Place samples in a beaker With water, bring to. boil and keep at boiling temperature for 30 minutes.
1.3. Remove samples from beaker, blot with filter
paper and weigh (mass m 2).
1.4. Enter the measurement results in table. 5.2.
1.5. Determine the water absorption of each sample using the formula
Table 5.2
2. Determine the water absorption and open porosity of glass-I ceramic materials.
2.1. Weigh samples of glass-ceramic materials. Measure the sample sizes required to calculate the volume with a caliper.
2.2. Place the samples in a beaker, bring to a boil and incubate at boiling temperature for 60 minutes.
2.3. Remove samples from beaker, weigh. Attention! Samples should not be thoroughly blotted, as water will be removed from relatively large holes.
2.4. Determine the water absorption of each sample using the above formula.
2.5. Determine the apparent density of samples using the formula
2.6. Calculate the apparent (open) porosity P to:
2.7. Enter the calculation results in Table 5.3.
Table 5.3
3. Based on the experimental results, conduct a comparative analysis and formulate conclusions.
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Direction " Materials science and technology of materials»
Basic educational programs:
Bachelor's degree: "Technology of materials and nanostructures"
No area of modern production can do without materials and technology for their production, especially in the field of high technologies, to which the activities of MIET belong. Recently, all over the world, much attention is paid to the development of nanotechnology, and, at the same time, the development of electronics has also entered the field of nanoscale. Thus, nanomaterials and nanomaterial technologies come to the fore.
Within the framework of the direction "Materials Science and Technology of Materials" (PMT), he graduates bachelors in the following profile:
Graduates of the PMT Institute, who received bachelor's and master's qualifications in the field of "Materials Science and Materials Technology", have good training in natural sciences, with an in-depth study of the features of research and creation of nanomaterials and nanostructures, which are the basis for the design and development of nanotechnology. They are fluent in user and special computer programs and are able to use modern programming languages to develop effective solutions to the assigned tasks.
The Institute possesses the latest equipment that allows it to conduct research and development of micro- and nano-materials and structures, methods of their research. Students who are interested in the work of the teachers of the institute, already from their junior years, take a full part in the work of scientific and technical groups in the development of various devices and writing software for them, the development of new technologies and the study of new materials. The results of this work are published in highly cited journals and collections, reported at conferences and seminars, and are often awarded diplomas and certificates. After successful graduation, many students continue their studies in graduate school. Postgraduates and students are actively interacting with colleagues from leading foreign universities in Europe and America, which includes not only the exchange of information, but also the possibility of continuing education and training for students, graduate students and young scientists abroad.
Graduates, together with teachers, have developed unique technologies for the formation of semiconductor energy converters, integrated and fiber optics technologies, which are world-renowned. The developed principles and methods are used in various foreign universities and firms. Postgraduates of the institute have repeatedly received grants and scholarships from the President of the Russian Federation.
Graduates of the PMT Institute are in demand in a number of priority areas of development of the world and Russian economy, such as:
- nanoengineering and nanomaterials;
- electronics and nanoelectronics;
- energy saving and alternative energy sources;
- space technologies;
- microelectromechanical systems.
The high level of training of personnel produced by the institute allows graduates to find employment in various other spheres of the economy, from energy to banking.
Materials Science and Technology of Materials
Introduction
The discipline "Materials Science and Technology of Materials" is one of the main disciplines of general technical training of a fire safety engineer in the specialty 330400 and is based on such disciplines of the State Educational Standard of Higher Professional Education as physics, chemistry, mathematics, engineering graphics and applied mechanics.
The discipline consists of two sections, structurally and methodically consistent with each other, which allows students not only to learn the nature of engineering materials, but also to study their properties depending on the chemical composition, structure and subsequent treatments. It is very important to consider familiarization with traditional and new technological processes for obtaining metallic and non-metallic materials, as well as technologies for obtaining blanks and finished products.
The test involves the students' independent development of the route technology for the manufacture of a specific product, taking into account all possible redistributions of metallurgical production. The training material must be considered in the sequence in which it is presented in the guidelines. Please read these instructions carefully before exploring each topic. Then, using the proposed literature, work out the training material with the obligatory outline. After completing each topic, answer the self-test questions.
Methodical instructions for the discipline program
Starting to study the course, it is necessary to understand the role of metallurgical and machine-building production in creating the material and technical base of the country and get acquainted with the directions of technical progress in these industries.
After studying the course, the student should know the main types of structural materials, methods of their production, as well as technological processes of shaping products and parts from structural materials.
Materials used for the manufacture of machine parts, structures and structures are called structural materials. The term "materials of construction" includes ferrous and non-ferrous metals, means a wide range of non-metallic materials such as plastics, rubber materials, as well as silicate glasses, sitalls and ceramics. Composite materials, materials and products of powder metallurgy are distinguished into a special group of structural materials. Structural materials must meet certain requirements, taking into account their mechanical, physicochemical, technological and operational properties.
When studying the course, special attention should be paid to the possibilities of obtaining one type of product by different methods of obtaining and the ability to conduct a technical and economic comparison of these methods.
Self-test questions
1. What metals and alloys are non-ferrous?
2. What metals and alloys are ferrous?
3. List the main groups of non-metallic materials of construction.
Section 1. TECHNOLOGY OF MATERIALS
The technology of structural materials is a body of knowledge about the methods of production of materials and the technology of their processing in order to manufacture blanks and products for various purposes. This section systematically and coherently includes various redistributions of modern production, allowing, with different processing accuracy and surface quality, to shape materials both on metal and non-metal bases.
Topic 1. Fundamentals of metallurgical production
Modern metallurgical production is a complex complex of various industries, based on ore deposits, coking coal, energy facilities
The student should understand the scheme of modern metallurgical production, taking into account all possible main and auxiliary redistributions. It is necessary to know the main types of products of ferrous and non-ferrous metallurgy.
1.1 Physical and chemical foundations of metallurgical production
In nature, almost all metals, due to their high chemical activity, are in a bound state in the form of various chemical compounds. Ore is a natural mineral that contains a metal that can be recovered in an economically viable industrial way. The task of metallurgy is to obtain metals and metal alloys from ores and other raw materials. For this, depending on the nature of the metal and the type of raw material, it is possible to use various methods. Explore the essence of recovery, electrolysis and metallothermy in metallurgical production. Consider the basic materials used in the production of metals from ores (industrial ore, fluxes, fuels, refractory materials).
Self-test questions
1. The structure of modern metallurgical production.
2. Materials for the production of metals and alloys.
3. The main types of metallurgical processes.
1.2. Pig iron production
Blast-furnace production is mainly used to smelt pig iron. When studying the process of obtaining pig iron, it is necessary to consider the device of a blast furnace and auxiliary units. The raw materials for the production of pig iron are iron and manganese ores, flux and fuel. When studying the characteristics of iron ores, one should learn that the metallurgical value of the ore is determined by the iron content in the ore, the possibility of ore beneficiation, the presence of harmful impurities, the physical state of the ore (porosity, lump size), and the composition of the waste rock. The main operations of ore preparation for smelting include crushing, concentration, agglomeration.
Of great importance for metallurgical processes are fluxes, that is, substances added during the smelting of ores to lower the melting point of waste rock and obtain a fluid slag. In addition, fluxes contribute to the refining of metal from harmful impurities and the removal of coke ash. Understand what fluxes are used in blast furnace production.
Cast iron production processes take place at high temperatures. It is necessary to study the properties and requirements for blast furnace fuel. It is also necessary to familiarize yourself with the types of refractory materials (acidic, basic, neutral).
The physicochemical essence of the blast-furnace process is as follows. In a blast furnace, the iron must be separated from the gangue, reduced to a metallic state, and finally combined with the correct amount of carbon to lower the melting point. To implement these changes, complex processes are required: 1) fuel combustion; 2) reduction of iron oxides and other elements; 3) carburizing iron; 4) slagging. These processes take place in the oven simultaneously, but with different intensities and at different levels of the oven. Consider each of these processes.
The products of blast furnace production are cast irons and ferroalloys of various grades, blast furnace slag, and blast furnace gas.
Work to improve the indicators of blast-furnace production is carried out in several directions: 1) improving the design of furnaces; 2) improving the preparation of charge materials; 3) intensification of the blast-furnace process; 4) improvement of systems of complex mechanization and automation of blast furnace process control.
Self-test questions
1. Tell us about the technological processes of ore preparation for production.
2. What is the role of flux in blast furnace production?
3. What types of fuels are used in a blast furnace?
4. Classification of refractory materials.
5. Physical and chemical processes in the blast furnace.
6. Draw a diagram of the internal profile of the blast furnace and name its main parts. Indicate the approximate temperatures in different areas of the blast furnace.
7. Why and in what units is the air supplied to the blast furnace heated?
8. What is achieved by using a blast enriched with oxygen, as well as humidification of the blast?
9. Name the products of blast-furnace smelting and indicate their areas of application.
10. Tell us about the measures taken to increase the productivity of the blast furnace.
1.3. Steel production
The main raw materials for steel production are pig iron and steel scrap (scrap).
Steel differs from cast iron in its lower content of carbon, silicon, manganese, sulfur and phosphorus. Removal of impurities, i.e. the conversion of cast iron into steel, occurs due to oxidative reactions that occur at high temperatures. Therefore, all methods of processing cast iron into steel are mainly reduced to the effect of oxygen on the cast iron at high temperatures. However, during the selective oxidation of carbon and other impurities, molten iron also absorbs some oxygen, which negatively affects the quality of the finished steel. Therefore, at the last stage of the steelmaking process, excess oxygen is bound into oxides of other metals and removed into slag, i.e., deoxidation is carried out with the addition of silicon, manganese and aluminum.
It is possible to convert cast iron into steel in various metallurgical units. The main ones are oxygen converters, open-hearth furnaces and electric furnaces.
Get acquainted with the device of these units, the principle of their operation, the peculiarities of the technological process of obtaining steel in them, the technical and economic indicators of their work.
In some cases, finished steel may not always meet the requirements for it. To obtain steels of especially high quality, special methods are used: casting steel in an inert atmosphere; processing with synthetic slag; vacuum degassing; electroslag, vacuum arc, electron beam and plasma arc remelting. Explore these ways.
Currently, almost all steelmaking processes are cyclic, intermittent. Replacing an intermittent process with a continuous one allows increasing the productivity of the units, improving the quality of steel. Get to know the principle of continuous steelmaking.
The progressive methods of obtaining steel (iron) include non-blast methods that make it possible to obtain directly from the ore, bypassing the blast furnace, metallic iron in the form of a sponge, crystal or liquid metal. It is necessary to study the schemes and features of these processes.
Finished steel is subjected to casting in order to obtain blanks. You should familiarize yourself with the design of the casting ladle and molds, as well as with the main methods of casting steel: casting from above, casting with a siphon, continuous casting. By the above methods, blanks are obtained, which are subsequently used for the manufacture of parts by various technological methods. The structure of metal ingots obtained in molds has a great influence on the properties of blanks. Study the structure of calm and boiling steel ingots.
Self-test questions
1. Indicate the main differences in chemical composition cast iron and sent.
2. Tell us about the physical and chemical nature of the conversion of cast iron into steel,
3. Purpose of the steel deoxidation process.
4. Oxygen-converter method of steel production. Its features and benefits.
5. The device of the open-hearth furnace and the principle of its operation.
6. Features of steel production in open-hearth furnaces.
7. Getting steel in arc and induction electric furnaces.
8. What are the technical and economic indicators for obtaining steel in converters, open-hearth and electric furnaces? Which of these methods of obtaining is more cost-effective and why?
9. List and describe the methods of obtaining high quality steels.
10. Steel-making units of continuous operation: device, principle of operation.
11. Tell us about non-blast methods of steel (iron) production.
12. Construction of a casting ladle and molds.
13. Methods for casting steel into molds.
14. Advantages of the continuous casting process.
15. The structure of an ingot of calm and boiling steel.
1.4. Non-ferrous metal production
Copper production. Copper is found in nature in the form of oxide and sulfide compounds. Hydrometallurgical and pyrometallurgical methods of copper extraction from copper ores have been developed. Study the pyrometallurgical method for producing copper, familiarize yourself with the physicochemical essence of each stage in the technological scheme of copper production.
Aluminum production. In terms of production volume, aluminum ranks second in the world after iron. The main raw material for aluminum production is bauxite. Aluminum is obtained by electrolysis of alumina dissolved in molten cryolite. This is a complex and energy-intensive process. Disassemble the scheme for obtaining aluminum and methods of refining it.
Titanium production. Titanium possesses a number of valuable properties: low specific gravity, high mechanical properties, good corrosion resistance. According to these indicators, titanium and its alloys are significantly superior to many metallic materials. However, the widespread use of titanium in modern technology is constrained by the high cost of this metal due to the extreme difficulty of extracting it from ores. One of the most widespread methods of obtaining titanium is the thermal magnesium method. Learn this method of making titanium.
Self-test questions
1. What are the main copper ores?
2. Tell us about the methods of concentration of copper ores.
3. Give a simplified scheme of copper production.
4. Give the industrial scheme of aluminum production
5. What are the raw materials for producing alumina and cryolite?
6. Name the main titanium ores.
7. Describe the essence of the magnesium-thermal method of titanium production.
1.5 Waste-free and resource-saving technologies in
metallurgical production
In the creation of waste-free and low-waste technologies in metallurgical production, the following areas can be distinguished:
1. Integrated use of metal ores. For example, from copper ores in the pyrometallurgical method of copper production, not only copper is extracted, but also gold, silver, selenium, tellurium; from titanomagnetites receive along with titanium and iron.
2. Use of materials from associated mining. It turns out that about 70% of overburden and mine rocks that go to dumps during mining are suitable for obtaining fluxes, refractory and building materials. Currently, only 3-4% of such materials are used.
3. Use of waste from coke-chemical and metallurgical industries. In these industries, there is an acute issue of processing all waste into products. At present, the following waste disposal processes are being implemented: in the by-product coke industry, ammonia, drugs, dyes, naphthalene and other substances are obtained from waste; In blast-furnace production, waste is used to obtain building materials (slag) and to heat the air blast entering the blast furnace (blast furnace gas). In the process of copper production and in passing, sulfuric acid is obtained from sulphurous waste gas.
4. Creation of closed loops. This implies the repeated use of certain substances in the production cycle. For example, in the production of titanium, after refining the titanium sponge, circulating magnesium is again sent to production - for titanium recovery.
Self-test questions
1. What are the main directions in the creation of waste-free technologies.
Topic 2. Basics of obtaining metal blanks
Starting to study this section, it is necessary to understand that the shaping of blanks, parts and products is possible when metals and alloys are found in various states of aggregation: in solid (pressure treatment, machining, welding), liquid (casting), gaseous (spraying). One of the criteria for choosing a method for forming blanks is the properties of the blank material, such as plasticity, hardness, weldability, casting properties, and a number of others.
2.1. Foundry technology fundamentals
Foundry is a branch of mechanical engineering that manufactures shaped parts by pouring molten metal into a mold, the cavity of which has the configuration of a part. The main advantages and advantages of producing castings are relative cheapness in comparison with other methods of manufacturing parts and the possibility of obtaining products of the most complex configuration from various alloys.
The suitability of alloys for the production of castings is determined by the following casting properties: fluidity, shrinkage, liquation, gas absorption. You should familiarize yourself with the casting properties of metals and alloys.
Currently, there are over 100 different methods of making casting molds and producing castings. Moreover, modern methods of producing billets by casting quite widely provide the specified accuracy, surface roughness parameters, physical and mechanical properties of the billets. Therefore, when choosing a method for obtaining a blank, it is necessary to evaluate all the advantages and disadvantages of each compared option.
In the general production of cast billets, a significant volume is occupied by casting in sandy-clay molds, which is explained by its technological versatility. This casting method is economically feasible for any type of production, for parts of any mass, configuration, dimensions, for producing castings from almost all casting alloys. The technological process of manufacturing cast fittings in sandy-clay molds consists of a significant number of operations: preparation of molding and core sands, making molds and cores, casting molds, releasing castings from molds, cutting and cleaning the casting. By changing the molding method, using different materials of models and molding mixtures, it is possible to obtain castings with a sufficiently clean surface and accurate dimensions.
Making casting molds from sandy-clay mixtures is the most difficult and responsible operation. It is necessary to study the technology of manufacturing casting molds for manual and machine molding, get acquainted with the casting technological equipment. Casting knockout and cleaning are the most labor-intensive and low-mechanized processes. You should remember the methods of knocking out castings, methods of cutting and cleaning castings, familiarize yourself with casting defects and measures to eliminate them.
Despite the versatility and low cost, the method of casting into sandy-clay molds is associated with a large flow of auxiliary materials and increased labor intensity. In addition, up to 25% of the mass of castings turns into shavings during machining.
In comparison with casting in sandy-clay molds, the advantage of special types of casting is as follows: in increasing the accuracy and improving the quality of the surface of the castings; reducing the mass of the gating system; a sharp decrease in the consumption of molding materials. In addition, the technological process of making castings by special methods is easily mechanized and automated, which increases labor productivity, improves the quality of castings, and reduces their cost.
Special casting methods include shell casting, precision investment casting, metal mold casting (chill molds), centrifugal casting, pressure casting and continuous casting in molds. You should carefully understand the essence, features and areas of application of special types of casting.
Self-test questions
1. Significance and scope of foundry.
2. Classification of methods for producing castings.
3. The main advantages of obtaining cast parts.
4. Casting properties of alloys.
5. Molding materials used for the manufacture of casting molds and cores.
6. What are the requirements for molding materials?
7. Basic operations when receiving castings.
8. Manual and machine molding when casting into sandy-clay molds.
9. Purpose and manufacture of rods.
10. Methods for knocking out and cleaning casting.
11. Describe the essence of the investment casting method, the advantages and disadvantages of this method.
12. The essence of the method of casting in shell molds and its advantages.
13. Indicate the advantages of casting in metal molds (chill molds).
14. Describe the essence of the injection molding method.
15. Describe the essence of obtaining shaped castings on centrifugal machines.
16. Scope of continuous casting.
Self-test questions
1. Describe the essence of the pressing process by direct and reverse methods.
2. The main tool and equipment for pressing.
3. Technology of the pressing process.
4. Pressing production.
5. What are the advantages and disadvantages of pressing as one of the MDM methods?
Drawing- cold deformation of metallic materials. In the process of cold plastic deformation, the metal is hardened (riveted). Drawn products have high dimensional accuracy and good surface quality. It is necessary to understand well the operations of the drawing process, especially in the operations of preliminary metal preparation, to study the drawing tool and equipment, the advantages and disadvantages of this method, and to know the products of drawing.
Self-test questions
1. Essence and peculiarity of the drawing process.
2. Schemes and principles of drawing mills.
3. Lug production.
Roll-formed profiles production- method of profiling sheet material in a cold state. In this case, shaped thin-walled profiles of a very complex configuration and large lengths are obtained. Understand the essence of this method and its scope.
Self-test questions
1. Tell us about the technological process of obtaining a bent profile from a sheet blank.
Free forging- hot working of metals by pressure, in which the deformation of the workpiece is carried out with a universal tool. During forging, the shape change occurs due to the flow of metal to the sides, perpendicular to the movement of the deforming tool - the striker. Forging is a rational and cost-effective process for obtaining high-quality workpieces with high mechanical properties in the conditions of small-scale and one-off production.
Familiarize yourself with the workpieces used in forging, open-die forging operations and related tools. Consider the equipment used in each case and the pros and cons of open-die forging.
Self-test questions
1. What is the essence of the open-die forging process?
2. What is a blank for forging?
3. What open-die forging operations do you know and what kind of forging tool is used?
Stamping- a kind of forging that allows you to mechanize and automate this process. Stamping is hot and cold, bulk and sheet. It is necessary to study the basic methods and operations of forging and sheet stamping, tools, equipment, advantages and disadvantages. Pay attention to the progressive methods of forging: cross-wedge rolling, rotary reduction, punching in split dies, etc.
Self-test questions
1. Compare forging and stamping. What kind of processing is more progressive? Why?
2. Describe the main stages of the hot forging process.
3. What are the original blanks for die forging?
4. Compare the advantages and disadvantages of open and closed die forging.
5. Draw diagrams of cold die forging operations.
6. What is the original blank and sheet stamping products?
7. What kind of sheet metal stamping operations do you know?
2.3. Basics of welding technology
Welding is the most progressive, high-performance and very economical technological method for obtaining permanent joints. Welding can be seen as an assembly operation (especially in the construction industry) and as a way of producing workpieces. In many areas of industry, combined welded parts are widely used, which consist of separate blanks made using different technological processes, and sometimes different materials. The part is dismembered into its component parts, followed by their welding, if the manufacture of it as one-piece or one-piece forged is associated with great production difficulties, lack of equipment, complication of machining, or if individual parts of the part work in especially harsh conditions (increased wear and temperature, corrosion, etc.). ) and their manufacture requires the use of more expensive materials.
Starting to study the welding section, it is necessary, first of all, to understand the physical essence of welding processes, which consists in the formation of strong atomic-molecular bonds between the surface layers of the workpieces being joined. To obtain a welded joint, it is required to clean the surfaces to be welded from contaminants and oxides, bring the surfaces to be joined together and give them some energy (activation energy). This energy can be communicated in the form of heat (thermal activation) and in the form of elastoplastic deformations (mechanical activation). Depending on the activation method, all welding methods are divided into three classes: thermal, thermomechanical and mechanical.
You should familiarize yourself with the possible source of heat during welding and with the criteria for weldability of materials, as well as pay attention to the manufacturability of welded joints.
Thermal class of welding- connection by melting using thermal energy (arc, electroslag, plasma, electron beam, laser, gas).
In arc welding, an electric arc between the workpiece and the electrode serves as a source of heat for melting the metal. Studying electric arc welding, the listener should get acquainted with the essence of the arc process, study the technology, equipment, fields of application of manual arc welding, as well as other methods of arc welding: automatic under a layer of flux and welding in a shielded gas environment. The issue of electroslag welding should be especially considered. It should be understood that the electric arc burns here only at the very beginning of the process in order to prepare the slag bath, and further melting of the filler and base metal is achieved due to the heat generated during the passage electric current through a slag bath.
Welding with an electron beam in a vacuum, a plasma jet, a laser beam belongs to special methods of electric welding. Consider the technology of these types of welding, the features of welded joints, the field of application.
A feature of gas welding is the use of a gas flame as a heat source. It is recommended to study the combustion process and the structure of the welding flame, the design of the gas torch, equipment and welding technology.
Next, you need to consider cutting metals. There are three main types of cutting: parting, surface cutting and oxygen lance cutting. Depending on the method of heating the metal to melting, oxygen, oxygen-flux, plasma, air-arc cutting of metals are distinguished.
Self-test questions
1. Describe the essence of the electric arc welding process.
2. Features and characteristics of welding with consumable and non-consumable electrodes.
3. Why are metal electrodes coated with coatings and what?
4. Manual arc welding.
5. Draw a diagram of automatic submerged arc welding.
6. Describe the essence of arc welding processes in a protective environment.
7. Draw a diagram of electroslag welding.
8. List and describe special methods of fusion welding.
9. Describe the technology of gas welding.
10. Tell us about the scope of gas welding.
Electrical contact welding refers to the types of welding with short-term heating of the joint and upsetting of heated workpieces. This is a highly productive type of welding, it is easily amenable to automation and mechanization, as a result of which it is widely used in mechanical engineering. It is necessary to familiarize yourself with electric resistance welding and its varieties: butt, spot, seam, relief. It is necessary to study in detail the technology, modes and equipment of electrical contact welding.
In diffusion welding, a joint is formed as a result of mutual diffusion of atoms of the surface layers of contacting materials. This welding method makes it possible to obtain high-quality joints of metals and alloys in homogeneous and dissimilar combinations. Understand the features of the technology and areas of application of diffusion welding.
Self-test questions
1. Draw and explain diagrams for spot, roll, seam and projection welding.
2. Give examples of the use of resistance welding in mechanical engineering.
3. Tell us in which sectors of the national economy diffusion welding is used.
Mechanical class of welding- welding carried out using mechanical energy and pressure without preheating the workpieces to be joined (cold welding, ultrasonic welding, explosion welding, friction welding). It is necessary to become familiar with the technology, advantages and field of application of these types of welding.
Self-test questions
1. Draw and explain the diagrams of the types of welding of the mechanical class.
Surfacing- a way to restore worn out and harden original parts. At present, various methods of surfacing and coating have been developed and are widely used. Surfacing is used to create surface layers on parts with the required properties. It is necessary to study the technology of various methods of surfacing, materials and equipment used in surfacing.
Self-test questions
1. Specify the techniques and methods of surfacing.
2. Tell us about the fields of application of hardfacing.
Soldering- the technological process of joining metal blanks without melting them by introducing molten metal - solder between them.
The solder has a melting point lower than the melting point of the metals to be joined. You should understand the physical nature of the soldering processes, know the soldering methods and types of soldered joints. It is important to understand when soft solder should be used and when hard solder should be used. It is necessary to study the areas of application of brazing metals and alloys.
Self-test questions
1. The physical nature of the soldering process.
2. What is the purpose of soldering flux?
3. What equipment is used for soldering?
The quality of welded and brazed joints is assessed using destructive control methods. It is necessary to study the external and internal defects of the joints and methods of their control.
Violation of the technological modes of welding leads in a number of cases to the appearance of stresses and deformations in welded joints. It is necessary to familiarize yourself with the measures to deal with the stresses arising from welding, and methods of correcting deformed elements and structures.
Self-test questions
1. List the defects in welded and soldered joints.
2. List the destructive and non-destructive methods of testing welded and soldered joints.
3. Name the reasons for the occurrence of residual stresses in welded structures.
4. How can the deformation of structures during welding be reduced or completely eliminated?
Topic 3. Fundamentals of dimensional processing of workpieces of machine parts
Dimensional processing is understood to mean giving the parts corresponding to the drawing of sizes and shapes by various cutting methods using specialized machines and tools. Cutting can be considered the final operation in the cycle of manufacturing various products of machine-building production, since only it provides a given quality of accuracy.
3.1. Basic information about the metal cutting process
Metal cutting is designed to give parts the required geometry with appropriate surface cleanliness. In this case, before the start of processing, the future part is called a workpiece, in the process of processing this workpiece is called a workpiece, and at the end of all types of processing, a finished part is obtained.
The metal layer that is removed during processing is called an allowance, and the removal of the allowance by hand corresponds to plumbing, and the removal of the allowance on machines corresponds to mechanical processing.
The movement of the executive bodies of metal-cutting machines is divided into workers and auxiliary. Determine which movements are called workers and schematically depict them in the figure. In doing so, note that the total movement of the cutting tool relative to the workpiece is called the resulting cutting movement.
When machining, the following types of operations are considered: turning, drilling, milling, planing, broaching, grinding. Understand that this division is relative, since any type of processing has a number of subspecies, for example, when drilling, countersinking, reaming, etc. are additionally used.
Under the diagrams and drawings given in the textbooks, understand the types of surfaces to be treated. When doing this, pay special attention to the geometry of the cutting tool using the example of a turning tool. The chip formation process is the main cutting mechanism and depends on the cutting force and cutting conditions. All this is characterized by cutting power. Based on these parameters, study the cutting specifications and understand the principles for selecting cutting data, including calculating the processing time.
Self-test questions
1. What movements during machining are called workers, and what auxiliary ones?
2. What types of surfaces are distinguished during machining?
3. What angles are distinguished in the cutting part of the tool:
4. What is meant by cutting planes in a static coordinate system?
5. Describe the process of chip formation.
6. What is meant by cutting force?
7. What operations include the cutting mode and how is it chosen?
8. How is the processing time calculated?
3.2. Cutting machine classification and technology
cutting
All metal-cutting machines are divided into groups according to the nature of the work performed and the type of tools used. Consider in detail the classification adopted in Russia and understand the unified convention for the designation of machine tools, understood as numbering. Then take a closer look at the cutting technologies performed on different metal cutting machines.
Processing on lathes. Using the pictures, consider the main components of a screw-cutting lathe and understand why lathes are often called universal. Analyze the types of lathe machines.
Processing on drilling and boring machines. Understand what is meant by the processing of round holes on the machines of the drilling group.
Processing on milling machines. Understand what milling is and what types of cutters are used for this.
Processing on planing, slotting and broaching machines. Taking into account the types of surface treatment with planing, highlight the features of this group of machines. Examine the type of tools used for these purposes. Make a diagram of work on the machines of this group.
Processing on grinding and finishing machines. Learn the grinding process and the tool used for this purpose. Please note that grinding is also a cutting operation and see why. Consider grinding techniques and types of grinders.
For all cutting technologies considered, study the possible types of work.
In conclusion, pay attention to the possibilities of mechanization and automation of metal-cutting machines. Understand what computer numerical control (CNC) machines are and how flexible automatic lines (HAPs) are assembled from them. Enter for yourself the concept of robots and manipulators.
Self-test questions
1. What are the lathes used for?
2. Why are lathes often called universal?
3. What is meant by countersinking and reaming of large holes.
4. What are the main types of cutters?
5. What are the features of planing machines?
6. What is meant by the grinding process?
7. What is meant by an abrasive tool?
8. For what purposes are robots and manipulators used in machining?
3.3. Electrophysicochemical treatment of materials
Compared to conventional metal cutting, these types of processing have a number of advantages: they allow processing materials with high mechanical properties, the processing of which is difficult or completely impossible by conventional methods (hard alloys, rubies, diamonds and even superhard materials), and also make it possible to process the most complex surfaces (holes with a curved axis, blind holes of a shaped profile, etc.).
All these methods are usually divided into two large groups, which include:
Electrophysical processing methods. Methods belonging to this group are most often called electroerosive and electro-beam, depending on the method of supplying energy to the surface to be treated.
Electric discharge machining of conductive metals and alloys is based on the phenomenon of local destruction of a material under the influence of a pulsed electric current passed between it and a special electrode.
The current discharges are carried out directly in the processing zone, where they are converted into heat, melting the particles of the processed metal.
Allocate:
Electrospark processing;
Electropulse processing;
Electrical contact-arc processing;
Ultrasonic treatment.
Electrobeam treatment is carried out on any materials and does not depend on their electrical conductivity. In this case, energy is supplied to the surface to be treated through the use of quantum generators (lasers) or electron beam guns.
Allocate:
Light beam processing (laser);
Electron beam processing.
Consider each method separately and sketch out the processing scheme in the synopsis.
Electrochemical processing methods. These methods are widely used in industry and are based on the anodic dissolution of the metal (anode) by passing a direct current through the electrolyte solution.
Allocate:
Electrochemical etching (polishing);
Dimensional electrochemical machining;
Electrochemical and mechanical processing;
Chemical and mechanical processing.
Understand for yourself the essence of each method, its capabilities and scope. Accompany the abstract with diagrams of the processing process.
Self-test questions
1. What is the essence of electrophysical processing methods?
2. Why can only electrically conductive materials be eroded?
3. What is the source of energy for ultrasonic treatment?
4. What technological operations can be carried out using lasers?
5. What is the essence of electrochemical processing methods?
6. For what purposes is electrochemical etching (polishing) used?
7. Why is one of the types of electrochemical processing called dimensional?
Topic 4. Fundamentals of technology for the production of blanks and parts
machines made of non-metallic and composite materials
Non-metallic materials include plastics, rubber materials, wood, silicate glasses, ceramics, sitalls and other materials.
Non-metallic materials are not only substitutes for metals, but they are often used as independent materials, sometimes even as irreplaceable ones (rubber, glass). Some materials have high mechanical and specific strength, lightness, thermal and chemical resistance, high electrical insulating characteristics, etc. The manufacturability of non-metallic materials should be especially noted. The use of non-metallic materials provides significant cost-effectiveness.
Non-metallic materials of construction
When studying non-metallic structural materials, it is necessary, first of all, to understand that polymers are the basis of non-metallic materials. It is known that polymer macromolecules are linear, branched, cross-linked and with a closed spatial network structure. The type of polymer macromolecules determines their behavior when heated. Depending on this, polymers are divided into thermoplastic and thermosetting. Study the structural features of polymers, their classification. Pay particular attention to the physical state and phase composition of the polymers.
Plastics are artificial materials derived from organic polymers. It is necessary to study the composition of simple and complex plastics, familiarize yourself with their properties and classification. Particular attention should be paid to the use of thermoplastic and thermosetting plastics.
The processing of plastics into products and parts is possible in all three physical states of polymers: viscous, highly elastic and solid. Moreover, the main shaping and production of blanks is carried out in a viscous-fluid state. The final shape and dimensions of plastic parts and products are carried out in a highly elastic and solid state. Explore ways to process plastics into products and how to make permanent joints from plastics by welding and gluing. Understand the nature of the techniques, the tools and equipment used.
An important group of polymers is rubbers, which form the basis of a separate class of structural materials - rubbers. As a technical material, rubber has high plastic properties. In addition, rubber has a number of important properties such as gas and water tightness, chemical resistance, valuable electrical properties, etc. Understand the composition of rubbers and the effect of various additives on their properties. Study the physical and chemical properties and applications of various brands of rubbers.
The technological scheme for the production of a rubber product includes the operations of preparing a rubber compound, molding it and vulcanization (chemical interaction between rubber and sulfur). Consider the methods of shaping rubber products and methods of obtaining rubber-fabric products.
A special group is made up of paints and varnishes and gluing materials. Understand for yourself what varnishes and enamels are. Here it is important to understand that these are complex multicomponent systems, which include different substances that provide the required set of properties. Highlight the characteristic features and make a classification of paints and varnishes.
The role of adhesives in modern production is very important. They make it possible to obtain permanent connections, including between materials that are completely different in nature. Study the classification of adhesives by composition and purpose, the peculiarities of their change and mechanical capabilities.
Self-test questions
1. What is called a polymer?
2. What is the basis for the classification of polymers as "thermoplastics" and "thermosets"?
3. What characterizes the crystalline state of polymers.
4. Tell about the three physical states of polymers: glassy (solid), highly elastic and viscous.
5. List the causes of polymer aging.
6. List the components and composition of complex plastics.
7. What fillers of plastics do you know?
8. Specify the field of application of thermoplastics and thermosets.
9. What are the advantages of plastics over metallic materials? What are their disadvantages?
10. What components are included in the composition of rubbers and how do they affect their properties?
11. Tell us about the technological methods of manufacturing rubber products.
12. What is the difference between oil paints and enamels?
13. What indicators characterize the quality of the adhesive bond?
Inorganic materials of construction
The group of inorganic materials includes inorganic glasses, glass-crystalline materials (sitalls), ceramics, graphite and asbestos. Understand that inorganic materials are based primarily on oxides and oxygen-free metal compounds. Please note that most of these materials contain various compounds of silicon with other elements and therefore they are often collectively referred to as silicate materials. Currently, the range of inorganic materials has expanded significantly. Pure oxides of aluminum, magnesium, zirconium, etc. are used, the properties of which are significantly superior to those of conventional silicon compounds. Consider the complex of physicochemical and mechanical properties of inorganic materials and compare it with those for organic polymer materials.
A special group is made up of natural inorganic materials, which include graphite, asbestos, wood and a number of rocks (marble, basalt, obsidian). Explore the features of these materials and their technical capabilities.
Self-test questions
1 What mineral materials are silicate glass?
2. What are sitalls, indicate the methods of obtaining them.
3. What is technical ceramics?
Composite structural materials
Artificial materials obtained by combining chemically dissimilar components are called composite materials. In composite materials, in contrast to alloys, the components retain their inherent properties and a clear interface is observed between them. There are natural (eutectic) and artificial composite materials.
Such a specialty as "Materials Science and Technology of Materials" has recently become in demand among applicants. Let's consider the main features of this area, its characteristics.
The area of professional activity of specialists
The direction "Materials Science and Technology of Materials" includes:
- research, development, use, modification, operation, disposal of materials of organic and inorganic nature in different directions;
- technologies for their creation, structure formation, processing;
- quality management for instrumentation and mechanical engineering, rocket and aviation technology, household and sports equipment, medical equipment.
Objects of Master's Activity
The specialty "Materials Science and Technology of Materials" is associated with the following objects of activity:
- with the main types of functional organic and inorganic materials; hybrid and composite materials; nano-coatings and polymer films;
- means and methods of diagnostics and testing, research and quality control of films, materials, coatings, blanks, semi-finished products, products, all types of test and control equipment, analytical equipment, computer software for processing results, as well as data analysis;
- technological production processes, processing and modification of coatings and materials, equipment, technological equipment, production chain management systems.
The specialty "Materials Science and Technology of Materials" presupposes possession of the skill of analyzing regulatory and technical documentation, certification systems for products and materials, and reporting documentation. The master must know the documentation on life safety and safety.
Directions of training
The specialty "Materials Science and Technology of Materials" is associated with training in the following types of professional activities:
- Research and analytical work.
- Production and design and technological activities.
- Organizational and managerial direction.
Having received the specialty "materials science and technology of materials", who to work with? A graduate who successfully passes the final certification receives the qualification “Master of Engineering”. He can find a job in various companies to carry out calculation, analytical and research activities.
In addition, the specialty "Materials Science and Technology of New Materials" makes it possible to conduct scientific and applied experiments, to participate in the processes of creating and testing innovative materials and new products.
Masters with such qualifications are engaged in the development of work plans, programs, methods aimed at creating technological recommendations for introducing innovations into the production process, and preparing certain tasks for ordinary workers.
Specificity of the direction
The specialty "Materials Science and Technology of Structural Materials" involves the preparation of publications, reviews, scientific and technical reports based on the results of the research. Such specialists systematize scientific, engineering, patent information on the research problem, reviews and conclusions on implemented projects.
Engineers who have mastered the direction of "materials science and technology of materials" are engaged not only in design and technology, but also in production activities.
Features of the direction
Engineers who have received such a specialization are engaged in the preparation of assignments for the development of project documentation, conduct patent research aimed at creating innovative areas. They are looking for the best options for processing and processing various materials, devices, installations, their technological equipment using automatic design systems.
Certified specialists assess the economic profitability of a certain technological process, take part in the analysis of alternative production methods, organize the processing and processing of products, participate in the process of certification of products and technologies.
Specificity of training
Bachelors in this profile are taught the following skills:
- select information about the available materials using databases, as well as a variety of literary sources;
- analyze, select, evaluate the performance of materials, while performing a complex structural analysis;
- communication skills, as well as the ability to work in a team;
- collect information in the field of ongoing experiments, draw up reports, reviews, certain scientific publications;
- to draw up documents, records, protocols of experiments.
Bachelors have the skills to check the projects being created for full compliance with all legislative standards. They design high-tech processes intended for initial research and design-technological structures, organize and equip workplaces with the necessary equipment.
Duties
Holders of a diploma with the direction of "materials science and technology of materials" are required to carry out equipment diagnostics. They pay special attention to environmental safety in the workplace. When developing technical specifications for creating certain units in complex mechanisms, engineers take into account their operational features.
After the completion of the work, they check the compliance of the results with the stated conditions, the safety of the created mechanisms. It is these specialists who prepare documents for registering new images, draw up special technical documentation.
Very often, graduates begin their professional career with the positions of "chemical and spectral analysis engineer", as well as "coating and materials test engineer".
Conclusion
Having received the specialty "Materials Science and Technology of Materials", the newly minted specialist will not have problems with employment. He can become an engineer at any large factory or combine. Those specialists who have certain knowledge in the field of metal processing and a diploma of higher education can count on the positions of a thermologist and defectoscopist.
A sufficient number of industrial enterprises and organizations of heavy industry are in need of metallurgists and metallographers. If you initially acquire theoretical knowledge in the field of metal processing, in this case, you can first find a job as an engineer, continue your studies, receiving the specialization "chemical and spectral analysis engineer" or "coating test engineer".
The specialty "Materials Science and Technology of Materials" has now become one of the main disciplines for those students who are engaged in mechanical engineering.
Students study the range of those materials that are already used in heavy industry, and also predict the creation of new substances intended for the metallurgical industry.
The specialty "Materials Science and Technology of Materials" is one of the most important disciplines for almost all students studying mechanical engineering. The creation of new developments that could compete in the international market cannot be imagined and carried out without a thorough knowledge of this subject.
The materials science course deals with the assortment of various raw materials and their properties. The various properties of the materials used determine the range of their application in technology. The internal structure of a metal or composite alloy directly affects product quality.
Basic properties
Materials science and engineering materials technology highlight the four most important characteristics of any metal or alloy. First of all, these are physical and mechanical features that make it possible to predict the operational and technological qualities of a future product. The main mechanical property here is strength - it directly affects the indestructibility of the finished product under the influence of working loads. The doctrine of fracture and strength is one of the most important components of the basic course "Materials Science and Technology of Materials". This science is for the search for the necessary structural alloys and components intended for the manufacture of parts with the required strength characteristics. Technological and operational features allow predicting the behavior of the finished product under operating and extreme loads, calculating the ultimate strength, and assessing the durability of the entire mechanism.
Basic materials
Over the past centuries, metal has been the main material for creating machines and mechanisms. Therefore, the discipline "materials science" pays great attention to metal science - the science of metals and their alloys. Soviet scientists made a great contribution to its development: Anosov P.P., Kurnakov N.S., Chernov D.K. and others.
The goals of materials science
Fundamentals of materials science are a must for future engineers. After all, the main purpose of including this discipline in the curriculum is to teach students of technical specialties to do right choice material for engineered products to extend their service life.
Achieving this goal will help future engineers solve the following tasks:
- Correctly assess the technical properties of a particular material by analyzing the conditions for manufacturing a product and its service life.
- Have a well-formed scientific understanding of the real possibilities of improving any properties of a metal or alloy by changing its structure.
- Know about all methods of hardening materials that can ensure the durability and performance of tools and products.
- Have up-to-date knowledge about the main groups of materials used, the properties of these groups and the field of application.
Required knowledge
The course "Materials Science and Technology of Structural Materials" is intended for those students who already understand and can explain the meaning of such characteristics as stress, load, plastic and aggregate state of matter, atomic-crystalline structure of metals, types of chemical bonds, basic physical properties of metals. In the process of studying, students undergo basic training, which will be useful for them to conquer specialized disciplines. The older courses cover a variety of manufacturing processes and technologies in which materials science and materials technology play an important role.
What to work with?
Knowledge of design features and technical characteristics metals and alloys will be useful either to a designer working in the field of operation of modern machines and mechanisms. Specialists in the field of technology of new materials can find their place of work in the engineering, automotive, aviation, energy, and space sectors. Recently, there has been a shortage of specialists with a degree in materials science and technology of materials in the defense industry and in the development of communications equipment.
Development of materials science
As a separate discipline, materials science is an example of a typical applied science explaining the composition, structure and properties of various metals and their alloys under different conditions.
Man acquired the ability to mine metal and make various alloys during the period of the decay of the primitive communal system. But as a separate science, materials science and materials technology began to be studied a little over 200 years ago. The beginning of the 18th century was the period of discoveries of the French scientist-encyclopedist Reaumur, who was the first to try to study the internal structure of metals. Similar studies were carried out by the English manufacturer Grignon, who in 1775 wrote a small message about the columnar structure he discovered, which forms when iron hardens.
In the Russian Empire, the first scientific works in the field of metallurgy belonged to M.V. Lomonosov, who in his leadership tried to briefly explain the essence of various metallurgical processes.
Metallurgy made a big leap forward in the early 19th century, when new methods of researching various materials were developed. In 1831, the works of P.P. Anosov showed the possibility of examining metals under a microscope. After that, several scientists from a number of countries scientifically proved structural transformations in metals during their continuous cooling.
A hundred years later, the era of optical microscopes ceased to exist. Structural materials technology could not make new discoveries using outdated methods. Optics have been replaced by electronic equipment. Metallurgy began to resort to electronic observation methods, in particular, neutron diffraction and electron diffraction. With the help of these new technologies, it is possible to increase the sections of metals and alloys up to 1000 times, which means that there are much more grounds for scientific conclusions.
Theoretical information about the structure of materials
In the process of studying the discipline, students receive theoretical knowledge about the internal structure of metals and alloys. At the end of the course, students should have acquired the following skills and abilities:
- about the internal;
- about anisotropy and isotropy. What causes these properties, and how they can be influenced;
- about various defects in the structure of metals and alloys;
- on the methods of studying the internal structure of the material.
Practical classes in the discipline of materials science
The Department of Materials Science is available in every technical university. During the period of passing a given course, the student studies the following methods and technologies:
- Foundations of Metallurgy - History and modern methods obtaining metal alloys. Steel and pig iron production in modern blast furnaces. Casting of steel and iron, methods of improving the quality of metallurgical production. Classification and marking of steel, its technical and physical characteristics. Smelting of non-ferrous metals and their alloys, production of aluminum, copper, titanium and other non-ferrous metals. The equipment used for this.
Modern development of materials science
Recently, materials science has received a powerful impetus for development. The need for new materials made scientists think about obtaining pure and ultrapure metals, work is underway to create various raw materials according to the originally calculated characteristics. Modern technology of construction materials offers the use of new substances instead of standard metallic ones. More attention is paid to the use of plastics, ceramics, composite materials, which have strength parameters compatible with metal products, but are devoid of their disadvantages.