Direction " Materials Science and Technology»

Main 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, which includes the activities of MIET. Recently, much attention has been paid to the development of nanotechnology all over the world, 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.

As part of the direction "Materials Science and Technology of Materials" (PMT) graduates bachelors in the profile:

Graduates of the PMT Institute, who received bachelor's and master's degrees in the field of "Materials Science and Technology of Materials", are well-trained in natural sciences, with an in-depth study of the features of the study and creation of nanomaterials and nanostructures, which are the basis for the design and development of nanotechnologies. They are fluent in custom and special computer programs and are able to use modern programming languages ​​to develop an effective solution to the tasks.

The Institute has the latest equipment, which makes it possible to carry out research and development of micro- and nano-materials and structures, as well as methods for their research. Students who are interested in the work of teachers of the institute, already from 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, presented at conferences and seminars, and are often awarded diplomas and diplomas. After successful completion of their studies, many students continue their studies in graduate school. Graduate students 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 of 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 recognized worldwide. The developed principles and techniques are used in various foreign universities and firms. Postgraduate students of the Institute have repeatedly been awarded grants and scholarships of the President of the Russian Federation.

Graduates of the PMT Institute are in demand in a number of priority areas 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 other various sectors of the economy from energy to banking.

Materials Science and Technology

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 for Higher Professional Education as physics, chemistry, mathematics, engineering graphics and applied mechanics.

The discipline consists of two sections, structurally and methodically coordinated with each other, which allows students not only to know the nature of engineering materials, but also to study their properties depending on the chemical composition, structure and subsequent processing. Acquaintance with traditional and new technological processes for obtaining metallic and non-metallic materials, as well as technologies for obtaining blanks and finished products can be considered very important.

The control work involves the independent development by students of the route technology for the manufacture of a particular product, taking into account all possible stages 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 studying each topic. Then, using the proposed literature, work through the educational material with the obligatory preparation of a summary. After studying each topic, answer the self-test questions.

Guidelines 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 to 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 for shaping products and parts from structural materials.

Structural materials are used for the manufacture of machine parts, structures and structures. The concept of "structural materials" includes ferrous and non-ferrous metals, implies a wide range of non-metallic materials, such as plastics, rubber materials, as well as silicate glasses, glass-ceramics and ceramics. Composite materials, materials and products of powder metallurgy are distinguished in a special group of structural materials. Structural materials must meet certain requirements, taking into account their mechanical, physico-chemical, technological and operational properties.

When studying the course, special attention should be paid to the possibilities of obtaining one type of product by various methods of obtaining and the ability to conduct a technical and economic comparison of these methods.

Questions for self-examination

1. What metals and alloys are non-ferrous?

2. What metals and alloys are ferrous?

3. List the main groups of non-metallic structural materials.

Section 1. TECHNOLOGY OF MATERIALS

The technology of structural materials is a set 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, which make it possible to form materials both on metal and non-metal bases with different processing accuracy and surface quality.

Topic 1. Basics of metallurgical production

Modern metallurgical production is a complex complex of various industries based on ore deposits, coking coal, energy capacities

The listener should understand the scheme of modern metallurgical production, taking into account all possible main and auxiliary stages. It is necessary to know the main types of products of ferrous and non-ferrous metallurgy.

1.1 Physical and chemical bases 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. An ore is a natural mineral raw material containing a metal that can be extracted in an economically advantageous industrial way. The task of metallurgy is to obtain metals and metal alloys from ores and other raw materials. To do this, depending on the nature of the metal and the type of feedstock, it is possible to use various methods. Disassemble the essence of recovery, electrolysis and metallothermy in metallurgical production. Consider the main materials used in the production of metals from ores (industrial ore, fluxes, fuels, refractory materials).

Questions for self-examination

1. The structure of modern metallurgical production.

2. Materials for the production of metals and alloys.

3. Main types of metallurgical processes.

1.2. Iron production

For the smelting of pig iron, blast-furnace production is mainly used. When studying the process of producing pig iron, it is necessary to consider the design of a blast furnace and auxiliary units. The starting 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 enriching the ore, the presence of harmful impurities, the physical state of the ore (porosity, size of pieces), and the composition of the waste rock. The main operations for preparing ore for smelting include crushing, enrichment, and agglomeration.

Of great importance for metallurgical processes are fluxes, i.e., substances added during the smelting of ores to lower the melting temperature of the 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. The properties and requirements for blast-furnace fuel should be studied. It is also necessary to familiarize yourself with the types of refractory materials (acidic, basic, neutral).

The physical and chemical essence of the domain process is as follows. In the blast furnace, the iron must be separated from the waste rock, reduced to a metallic state, and finally combined with the right amount of carbon to reduce the melting point. To implement these changes, complex processes are required: 1) fuel combustion; 2) reduction of oxides of iron and other elements; 3) carburization of iron; 4) slag formation. These processes take place in the furnace simultaneously, but with different intensity and at different levels of the furnace. Consider each of these processes.

The products of blast furnace production are cast iron and ferroalloys of various grades, blast furnace slag, and top gas.

Work to improve the indicators of blast-furnace production is being carried out in several directions: 1) improving the design of furnaces; 2) improving the preparation of charge materials; 3) intensification of the domain process; 4) improvement of systems of complex mechanization and automation of blast-furnace process control.

Questions for self-examination

1. Tell us about the technological processes of preparing ore for production.

2. What is the role of flux in blast furnace production?

3. What types of fuel are used in the blast furnace?

4. Classification of refractory materials.

5. Physical and chemical processes occurring in a blast furnace.

6. Draw a diagram of the internal profile of a blast furnace and name its main parts. Give approximate temperatures in various parts 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 an oxygen-enriched blast, as well as by moistening the blast?

9. Name the products of blast-furnace smelting and indicate their areas of application.

10. Tell us about the activities 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 a lower content of carbon, silicon, manganese, sulfur and phosphorus. The 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 pig iron into steel are reduced mainly to the effect of oxygen on pig iron at high temperatures. However, during the selective oxidation of carbon and other impurities, the molten iron also absorbs some oxygen, which adversely 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.

Familiarize yourself with the device of these units, the principle of their operation, the features 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. For obtaining steels 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.

At present, almost all steel-smelting processes are cyclic, discontinuous. Replacing a discontinuous process with a continuous one makes it possible to increase the productivity of the units and improve the quality of steel. Familiarize yourself with the principle of operation of continuous steelmaking units.

Progressive methods of obtaining steel (iron) include non-domain methods, which make it possible to obtain directly from the ore, bypassing the blast furnace, metallic iron in the form of a sponge, cracker 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 be familiar with the construction of the pouring ladle and molds, as well as with the main methods of pouring steel: pouring from above, pouring by siphon, continuous casting. By the listed 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 ingots of calm and boiling steel.

Questions for self-examination

1. Indicate the main differences in the chemical composition of cast iron and slal.

2. Tell us about the physical and chemical nature of the redistribution 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 an open-hearth furnace and the principle of its operation.

6. Features of steel production in open-hearth furnaces.

7. Obtaining steel in arc and induction electric furnaces.

8. What technical and economic indicators characterize the production of 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 for obtaining high-quality steels.

10. Steel-smelting units of continuous operation: device, principle of operation.

11. Tell us about non-domain methods of obtaining steel (iron).

12. Arrangement of pouring ladle and molds.

13. Methods for pouring steel into molds.

14. Advantages of the process of continuous casting of steel.

15. The structure of an ingot of calm and boiling steel.

1.4. Production of non-ferrous metals

Copper production. Copper is found in nature in the form of oxide and sulfide compounds. Hydrometallurgical and pyrometallurgical methods for extracting copper from copper ores have been developed. Study the pyrometallurgical method of obtaining copper, get acquainted with the physical and chemical essence of each stage in the technological scheme of copper production.

Aluminum production. In terms of production, aluminum ranks second in the world after iron. The main raw material for producing aluminum 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 for its refining.

Titanium production. Titanium has 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 common methods for obtaining titanium is the magnesium thermal method. Learn this way to produce titanium.

Questions for self-examination

1. Name the main ores of copper.

2. Tell us about the methods of enrichment of copper ores.

3. Give a simplified copper production scheme.

4. Give an industrial scheme for the production of aluminum

5. What is the raw material for producing alumina and cryolite?

6. Name the main ores of titanium.

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. Comprehensive 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, and tellurium; along with titanium, iron is also obtained from titanomagnetites.

2. Use of associated mining materials. 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, the issue of processing all waste into products is acute. Currently, the following waste disposal processes are being implemented: in the coke industry, ammonia, medicines, dyes, naphthalene and other substances are obtained from waste; in blast furnace production, waste is used to produce building materials (slag) and to heat the air blast entering the blast furnace (top gas). In the process of copper production and incidentally receive sulfuric acid from the off-gas.

4. Creation of closed cycles. It implies the repeated use of certain substances in the production cycle. For example, in the production of titanium, after refining a titanium sponge, circulating magnesium is again sent to production - to restore titanium.

Questions for self-examination

1. Name the main directions in the creation of non-waste technologies.

Topic 2. Fundamentals 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 in various states of aggregation: in solid (forming, machining, welding), liquid (casting), gaseous (spraying). One of the criteria for choosing a method for forming blanks is the properties of the material of the blanks, such as plasticity, hardness, weldability, casting properties, and a number of others.

2.1. Fundamentals of foundry technology

Foundry is a branch of mechanical engineering engaged in the manufacture of shaped parts by pouring molten metal into a mold, the cavity of which has the shape of a part. The main advantages and advantages of producing castings are the relative cheapness compared to 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, segregation, gas absorption. Familiarize yourself with the casting properties of metals and alloys.

Currently, there are more than 100 different ways of making molds and obtaining castings. Moreover, modern methods for producing blanks by casting provide the specified accuracy, surface roughness parameters, physical and mechanical properties of blanks quite widely. Therefore, when choosing a method for obtaining a workpiece, it is necessary to evaluate all the advantages and disadvantages of each compared option.

In the general production of cast billets, casting in sand-clay molds occupies a significant volume, which is explained by its technological versatility. This method of casting is economically feasible for any type of production, for parts of any weight, configuration, dimensions, for producing castings from almost all casting alloys. The technological process of manufacturing cast fittings in sand-clay molds consists of a significant number of operations: preparation of molding and core sands, making molds and cores, pouring molds, releasing castings from molds, trimming and cleaning castings. By changing the molding method, using different materials of models and molding sands, it is possible to obtain castings with a fairly clean surface and accurate dimensions.

Making molds from sand-clay mixtures is the most complex and responsible operation. It is necessary to study the technology of manufacturing molds for manual and machine molding, to get acquainted with the foundry tooling. Knockout and cleaning of castings are the most labor-intensive and low-mechanized processes. You should remember the methods of knocking out castings, the methods of cutting and cleaning castings, familiarize yourself with the defects of castings and measures to eliminate them.

Despite the versatility and low cost, the method of casting in sand-clay molds is associated with a large traffic flow of auxiliary materials, increased labor intensity. In addition, up to 25% of the mass of castings is converted into chips during machining.

Compared with casting in sand-clay molds, the advantage of special types of casting is as follows: to increase the accuracy and improve the quality of the surface of the castings; weight reduction of the gating system; a sharp decrease in the consumption of molding materials. In addition, the technological process of manufacturing castings using 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 mold casting, investment casting, mold casting, centrifugal casting, injection molding and continuous casting in molds. You should carefully understand the essence, features and applications of special types of casting.

Questions for self-examination

1. Significance and scope of foundry production.

2. Classification of methods for obtaining castings.

3. The main advantages of obtaining cast parts.

4. Casting properties of alloys.

5. Molding materials used for the manufacture of molds and cores.

6. What are the requirements for molding materials?

7. Basic operations in the production of castings.

8. Manual and machine molding when casting in sand-clay molds.

9. Appointment and manufacture of rods.

10. Methods for knocking out and cleaning castings.

11. Describe the essence of the investment casting method, the advantages and disadvantages of this method.

12. The essence of the method of casting into shell molds and its advantages.

13. Specify the advantages of casting in metal molds (chill molds).

14. Describe the essence of the injection molding method.

15. State the essence of obtaining shaped castings on centrifugal machines.

16. Scope of continuous casting.

Questions for self-examination

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. Products of pressing.

5. What are the advantages and disadvantages of pressing as one of the OMD methods?

Drawing- deformation of metal materials in a cold state. In the process of cold plastic deformation, the metal is hardened (riveted). Drawing products have high dimensional accuracy and good surface quality. It is necessary to have a good understanding of the operations of the technological process of drawing, especially in the operations of preliminary preparation of metal, to study the drawing tool and equipment, the advantages and disadvantages of this method, and to know the products of drawing.

Questions for self-examination

1. Essence and features of the drawing process.

2. Schemes and principles of work of drawing mills.

3. Drawing products.

Production of roll-formed profiles- a method of profiling sheet material in a cold state. In this case, shaped thin-walled profiles of a very complex configuration and great length are obtained. Understand the essence of this method and its scope.

Questions for self-examination

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 by 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 blanks with high mechanical properties in small-batch and single-piece production.

Familiarize yourself with the blanks used in forging, free forging operations and related tools. Consider the equipment used in each case, the advantages and disadvantages of free forging.

Questions for self-examination

1. What is the essence of the free forging process?

2. What is the forging workpiece?

3. What kind of free forging operations do you know and what kind of forging tool is used?

Stamping- a kind of forging, which allows mechanizing and automating this process. Stamping is hot and cold, bulk and sheet. It is necessary to study the basic methods and operations of volumetric and sheet stamping, tools, equipment, advantages and disadvantages. Pay attention to progressive forging methods: cross-wedge rolling, rotational compression, split die forging, etc.

Questions for self-examination

1. Compare forging and stamping. Which type of processing is more advanced? Why?

2. Describe the main stages of the hot forging process.

3. What are the initial blanks for forging?

4. Compare the advantages and disadvantages of forging in open and closed dies.

5. Draw diagrams of cold forging operations.

6. What is the original workpiece and sheet metal products?

7. What kind of sheet metal stamping operations do you know?

2.3. Fundamentals of welding technology

Welding is the most progressive, high-performance and very economical technological method for producing permanent joints. Welding can be seen as an assembly operation (especially in the construction industry) and as a way to produce workpieces. In many industries, composite weldments are widely used, which consist of separate blanks made using different technological processes, and sometimes different materials. The part is divided into its component parts with their subsequent welding, if the manufacture of its solid or solid forged one is associated with great production difficulties, lack of equipment, complication of machining, or if individual parts of the part work under especially difficult 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 the welding processes, which consists in the formation of strong atomic-molecular bonds between the surface layers of the workpieces to be joined. To obtain a welded joint, it is required to clean the welded surfaces from impurities and oxides, bring the surfaces to be joined together and impart some energy (activation energy) to them. This energy can be transferred in the form of heat (thermal activation) and in the form of elastic-plastic deformations (mechanical activation). Depending on the activation method, all welding methods are divided into three classes: thermal, thermomechanical and mechanical.

You should be familiar with the possible source of heat during welding and with the criteria for the weldability of materials, as well as pay attention to the manufacturability of welded joints.

Thermal class welding- connection by melting using thermal energy (arc, electroslag, plasma, electron beam, laser, gas).

In arc welding, the heat source for melting the metal is an electric arc that occurs between the workpiece and the electrode. Studying electric arc welding, the student should get acquainted with the essence of the arc process, study the technology, equipment, areas of application of manual arc welding, as well as other methods of arc welding: automatic submerged arc welding and welding in shielding gases. Special consideration should be given to the issue of electroslag welding. 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 released when the electric current passes through the slag bath.

Welding with an electron beam in a vacuum, plasma jet, laser beam refers to special methods of electric welding. Consider the technology of these types of welding, features of welded joints, scope.

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 burner, equipment and welding technology.

The next thing to consider is metal cutting. There are three main types of cutting: separation, surface cutting and oxyfuel cutting. Depending on the method of heating the metal to melting, there are oxygen, oxygen-flux, plasma, air-arc cutting of metals.

Questions for self-examination

1. State the essence of the electric arc welding process.

2. Features and characteristics of consumable and non-consumable electrode welding.

3. Why are metal electrodes coated with coatings and what kind?

4. Manual arc welding.

5. Draw a diagram of automatic submerged arc welding.

6. State 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. State the technology of gas welding.

10. Tell us about the scope of gas welding.

Electrocontact welding refers to the types of welding with short-term heating of the junction and draft of heated workpieces. This is a high-performance 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 electric resistance welding.

In diffusion welding, a joint is formed as a result of mutual diffusion of atoms of the surface layers of the contacting materials. This method of welding makes it possible to obtain high-quality joints of metals and alloys in homogeneous and heterogeneous combinations. Understand the technology features and applications of diffusion welding.

Questions for self-examination

1. Draw and explain the schemes of spot, roller, seam and projection electric resistance 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 Welding Class- welding carried out using mechanical energy and pressure without preheating of the workpieces to be joined (cold welding, ultrasonic welding, explosion welding, friction welding). It is necessary to familiarize yourself with the technology, advantages and scope of these types of welding.

Questions for self-examination

1. Draw and explain the diagrams of the types of welding of the mechanical class.

Surfacing- a method of restoring worn and hardening of the original parts. Currently, various methods of surfacing and coating are developed and widely used. Surfacing is used to create surface layers on parts with the required properties. It is necessary to study the technology of various surfacing methods, materials and equipment used in surfacing operations.

Questions for self-examination

1. Indicate the techniques and methods of surfacing.

2. Tell us about the areas of application of hardfacing.

Soldering- the technological process of joining metal blanks without their melting by introducing molten metal between them - solder.

The solder has a melting point lower than the melting point of the metals being joined. It is necessary to understand the physical essence of the soldering processes, to know the methods of soldering and the types of solder joints. It is important to understand in which cases soft solder should be used, and in which hard solder. It is necessary to study the scope of soldering metals and alloys.

Questions for self-examination

1. The physical essence of the soldering process.

2. What is the purpose of the flux when soldering?

3. What equipment is used for soldering?

The quality of welded and soldered joints is evaluated using destructive control methods. It is necessary to study the external and internal defects of the joints and methods for their control.

Violation of the technological modes of welding leads in some cases to the occurrence of stresses and deformations in welded joints. It is necessary to familiarize yourself with the measures to deal with stresses arising during welding, and ways to correct deformed elements and structures.

Questions for self-examination

1. List the defects of welded and soldered joints.

2. List the destructive and non-destructive methods of control of welded and soldered joints.

3. Name the causes 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 blanks for machine parts

Dimensional processing is understood as giving the details of the dimensions and shapes corresponding to the drawing by various cutting methods using specialized machines and tools. Machining 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 process of metal cutting

Metal cutting is designed to give parts the required geometry with the appropriate surface finish. At the same time, before the start of processing, the future part is called a workpiece, during processing this workpiece is called a workpiece, and at the end of all types of processing, a finished part is obtained.

The layer of metal that is removed during processing is called the allowance, and the removal of the allowance by hand corresponds to metalwork, and the removal of the allowance on machine tools corresponds to machining.

The movement of the executive bodies of metal-cutting machines is divided into working and auxiliary. Understand what movements are called workers and schematically depict them in the figure. In this case, 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.

According to the diagrams and drawings given in the textbooks, understand the types of surfaces to be processed. In this case, pay special attention to the geometry of the cutting tool using the example of a turning tool. The process of chip formation is the main cutting mechanism and depends on the cutting force and cutting mode. All this is characterized by cutting power. Based on these parameters, study cutting guidelines and understand the principles of cutting data selection, including the calculation of machining time.

Questions for self-examination

1. What movements during machining are called working, and which are auxiliary?

2. What types of surfaces are isolated 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 processing time calculated?

3.2. Classification of cutting machines 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 system symbol machine tools, understood as numbering. Then, consider in detail the cutting technologies performed on various metal cutting machines.

Machining on lathes. Using the illustrations, examine the main components of a screw-cutting lathe and understand why lathes are often called universal lathes. Analyze the types of machines of the turning group.

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. Considering the types of surface treatment by planing, highlight the features of this group of machines. Study the type of tools used for these purposes. Make a scheme of work on the machines of this group.

Processing on grinding and finishing machines. Learn the grinding process and the tools used for this purpose. Please note that grinding also applies to cutting operations and understand what this is connected with. Consider grinding methods 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 machine tools. Understand what numerical control (CNC) machines are and how flexible automatic lines (FAPs) are assembled from them. Enter for yourself the concept of robots and manipulators.

Questions for self-examination

1. What are the machines of the turning group 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 planers?

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. Electrophysical and chemical processing 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 with conventional methods (hard alloys, rubies, diamonds, and even superhard materials), and also makes 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 methods of processing. Methods belonging to this group are most often called electroerosive and electrobeam, depending on the method of supplying energy to the treated surface.

Electroerosive machining of conductive metals and alloys is based on the phenomenon of local destruction of the material under the action of a pulsed electric current passed between it and a special electrode.

Current discharges are carried out directly in the processing zone, where they are converted into heat, melting particles of the metal being processed.

Allocate:

electrospark processing;

Electropulse processing;

Electrocontact-arc processing;

ultrasonic processing.

Electrobeam processing is carried out on any materials and it does not depend on their electrical conductivity. In this case, energy is supplied to the treated surface through the use of quantum generators (lasers) or electron beam guns.

Allocate:

Light beam processing (laser);

Electron beam processing.

Consider each method separately and draw a processing scheme in the abstract.

Electrochemical processing methods. These methods are widely used in industry and are based on the anodic dissolution of the metal (anode) by passing through a direct current electrolyte solution.

Allocate:

Electrochemical etching (polishing);

Dimensional electrochemical processing;

Electrochemical-mechanical processing;

Chemical-mechanical processing.

Understand for yourself the essence of each method, its capabilities and scope. Accompany the abstract with diagrams of the processing process.

Questions for self-examination

1. What is the essence of electrophysical processing methods?

2. Why can only electrically conductive materials be subjected to electroerosive machining?

3. What is the source of energy in ultrasonic processing?

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

The concept of "non-metallic materials" includes plastics, rubber materials, wood, silicate glasses, ceramics, glass-ceramics and other materials.

Non-metallic materials are not only substitutes for metals, but they are often used as independent, sometimes even as irreplaceable (rubber, glass). Individual materials have high mechanical and specific strength, lightness, thermal and chemical resistance, high electrical insulating characteristics, etc. Of particular note is the manufacturability of non-metallic materials. The use of non-metallic materials provides significant economic efficiency.

Non-metallic construction materials

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 special attention to the physical state and phase composition of the polymers.

Plastics are man-made materials derived from organic polymers. It is necessary to study the composition of simple and complex plastics, to get acquainted 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 preparation of blanks is carried out in a viscous-fluid state. Giving the final shape and dimensions to plastic parts and products is carried out in a highly elastic and solid state. Learn how to process plastics into products and how to obtain permanent joints from plastics by welding and gluing. Understand the essence of the methods, the tools and equipment used.

An important group of polymers are rubbers, which form the basis of a separate class of structural materials - rubbers. As a technical material, rubber is characterized by high plastic properties. In addition, rubber has a number of important properties such as gas and water impermeability, 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 rubbers of various grades.

The technological scheme for the production of rubber products includes the preparation of a rubber mixture, its molding and vulcanization (chemical interaction of rubber and sulfur). Consider the methods of shaping rubber products and methods for obtaining rubber-fabric products.

A special group is made up of paints and varnishes and adhesives. Find out 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 large. 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 features of their change and mechanical capabilities.

Questions for self-examination

1. What is called a polymer?

2. What underlies the classification of polymers as "thermoplastics" and "thermoplastics"?

3. What characterizes the crystalline state of polymers.

4. Tell us about the three physical states of polymers: glassy (solid), highly elastic and viscous.

5. List the reasons for the aging of polymers.

6. List the components included and the composition of complex plastics.

7. What kind of plastic fillers do you know?

8. Indicate the scope of thermoplastics and thermoplastics.

9. What are the advantages of plastics over metal materials? What are their disadvantages?

10. What components are included in the composition of rubber 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 joint?

Inorganic construction materials

The group of inorganic materials includes inorganic glasses, glass-ceramic materials (sitalls), ceramics, graphite and asbestos. Understand that the basis of inorganic materials are mainly 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 combined under the general name - silicate materials. Currently, the range of inorganic materials has expanded significantly. Pure oxides of aluminium, 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 similar indicators for organic polymeric materials.

A special group is made up of natural inorganic materials, which include graphite, asbestos, wood and a number of rocks (marble, basalt, obsidian). Study the features of these materials and their technical capabilities.

Questions for self-examination

1 What mineral materials are silicate glass?

2. What are glass-ceramics, indicate the ways of obtaining them.

3. What is technical ceramics?

Composite structural materials

Composite materials are artificial materials obtained by combining chemically dissimilar components. In composite materials, unlike alloys, the components retain their inherent properties and there is a clear interface between them. Allocate natural (eutectic) and artificial composite materials.

Such a specialty as "Materials Science and Technology of Materials" has recently become in demand among applicants. Consider the main features of this direction, its characteristics.

Area of ​​professional activity of specialists

The direction "Materials science and technology of materials" includes:

• research, development, use, modification, operation, utilization of materials of organic and inorganic nature in various directions;
• technologies for their creation, structure formation, processing;
• quality management for instrumentation and mechanical engineering, rocket and aviation equipment, household and sports equipment, medical equipment.

Objects of activity of masters

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; nanocoatings 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 testing 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" involves the 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.

Areas of training

The specialty "Materials Science and Technology of Materials" is associated with training in the following types of professional activities:

• Research and calculation and analytical work.
• Production and design and technological activities.
• Organizational and managerial direction.

Having received the specialty "materials science and technology of materials", what to work with? A graduate who successfully passes the final attestation receives the qualification "Master-Engineer". He can find a job in various companies in order to carry out settlement and analytical and research activities.

In addition, the specialty "Materials Science and Technology of New Materials" makes it possible to conduct scientific and applied experiments, 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, preparing certain tasks for ordinary workers.

Direction specifics

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 carry out the systematization of 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 technological, but also in production activities.

Direction features

Engineers who have received such a specialization prepare tasks for the development of project documentation, conduct patent research aimed at creating innovative directions. They are looking for the best options for the processing and processing of various materials, devices, installations, their technological equipment using automatic design systems.

Certified specialists assess the economic viability of a certain technological process, take part in the analysis of alternative methods of production, organize the processing and processing of products, participate in the process of certification of products and technologies.

The specifics of training

Bachelors in this profile are trained in the following skills:

• select information about available materials using databases, as well as a variety of literary sources;
• analyze, select, evaluate materials according to operational characteristics, while performing a structural complex 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;
• draw up documents, records, protocols of experiments.

Bachelors have the skills to check created projects for full compliance with all legal regulations. They design high-tech processes intended for initial research and design and technological structures, organize and equip workplaces with the necessary equipment.

Responsibilities

Diploma holders with the direction "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 nodes in complex mechanisms, engineers take into account their operational features.

After completion of the work, they check the compliance of the results obtained with the declared conditions, the safety of the created mechanisms. It is these specialists who prepare documents for the registration of new images and draw up special technical documentation.

Very often, graduates start their professional career with the position of "chemical and spectral analysis engineer", as well as "coatings 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 thermal technologist and flaw detector.

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 education, having received 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 is impossible to imagine and implement without a thorough knowledge of this subject.

The course of materials science deals with the study of the range of various raw materials and their properties. Various properties of the materials used predetermine the range of their application in engineering. The internal structure of the metal or composite alloy directly affects the quality of the product.

Basic properties

Materials Science and Structural Materials Technology note 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 work loads. The doctrine of destruction and strength is one of the most important components basic course"Materials Science and Technology of Materials". This science is to find the right structural alloys and components for the manufacture of parts with the desired strength characteristics. Technological and operational features make it possible to predict the behavior of the finished product under working and extreme loads, calculate the strength limits, and evaluate the durability of the entire mechanism.

Basic materials

Over the past centuries, metal has been the main material for the creation of machines and mechanisms. Therefore, the discipline "materials science" pays great attention to metal science - the science of metals and their alloys. A great contribution to its development was made by Soviet scientists: Anosov P.P., Kurnakov N.S., Chernov D.K. and others.

Goals of materials science

The fundamentals of materials science are mandatory for future engineers to study. After all, the main goal of including this discipline in training course is teaching technical students to do right choice material for engineered products to extend their lifespan.

Achieving this goal will help future engineers solve the following tasks:

• Correctly evaluate the technical properties of a particular material, analyzing the conditions of manufacture of the product and its service life.
• Have well-formed scientific ideas about the real possibilities of improving any properties of a metal or alloy by changing its structure.
• Know about all methods of strengthening 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 scope.

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 to them to conquer the specialized disciplines. More senior courses consider various production processes and technologies, in which materials science and technology play a significant role.

Who to work?

Knowledge of the design features and technical characteristics of 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 diploma in "materials science and technology" in the defense industry and in the development of communications.

Development of materials science

As a separate discipline, materials science is an example of a typical applied science that explains the composition, structure and properties of various metals and their alloys under different conditions.

Man acquired the ability to extract metal and produce various alloys during the period of decomposition 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 is the period of discoveries by the French encyclopedist Réaumur, 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 short report on the columnar structure that he discovered, which is formed during the solidification of iron.

In the Russian Empire, the first scientific works in the field of metal science belonged to M. V. Lomonosov, who in his manual tried to briefly explain the essence of various metallurgical processes.

Metal science made a big leap forward at the beginning of the 19th century, when new methods for studying 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. The technology of structural materials could not make new discoveries using outdated methods. Optics have been replaced by electronics. Metal science began to resort to electronic methods of observation, 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;
• about methods of studying the internal structure of the material.

Practical classes in the discipline of materials science

There is a department of materials science in every technical university. During the course of a given course, the student studies the following methods and technologies:

• Fundamentals of metallurgy - history and modern methods of obtaining metal alloys. Production of steel and iron in modern blast furnaces. Casting of steel and cast iron, methods of improving the quality of products 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. 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 initially calculated characteristics. Modern technology construction materials offers the use of new substances instead of standard metal ones. More attention is paid to the use of plastics, ceramics, composite materials, which have strength parameters that are compatible with metal products, but are devoid of their shortcomings.

Ministry of Education of the Republic of Belarus

BELARUSIAN NATIONAL

TECHNICAL UNIVERSITY

Department of "Information-measuring equipment and technologies"

LABORATORY WORKS

(WORKSHOP)

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 workshop plays an important role. Without mastering the skills of using the analysis of the behavior of materials under various conditions, a directed synthesis of new materials and their reasonable use in practice is impossible.

Performing laboratory work will allow you to consolidate the theoretical provisions of the main sections of the science of materials, get acquainted with modern techniques scientific research and analyze the obtained experimental results. As a result, you can perform a small, fully completed scientific study.

The textbook (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 contains a list of additional literature, which will contribute to a more detailed study of the work.

The purpose of the manual is to familiarize with the various metallic and non-metallic structural materials used in instrumentation, and the acquisition by students of clear ideas about the diverse nature of physical and chemical phenomena occurring in materials during 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 obtained results and conclusions. When conducting laboratory work, it is necessary to strictly adhere to safety requirements.

laboratory work number 1

STUDY OF THE STRUCTURE OF METALS AND THEIR ALLOYS

Goal of the work: study the "iron-carbon" state diagram, get acquainted with the microstructure of iron-carbon alloys (steels and cast irons), powder composite materials.

Theoretical part

When the concentration of components in alloys changes, 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 diagrams state, which is a graphical representation of the state of the alloys. Diagrams are built for the equilibrium state of alloys. equilibrium state- 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 for their construction. With its help, cooling curves of 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. Using state diagrams, the melting and polymorphic transformation temperatures 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 for studying transformations in the solid state, 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 binary alloys, the temperature is plotted vertically, and the concentration of components is plotted horizontally. Each point on the x-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 of 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 should decrease.

The type of the state 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 in the liquid state there is unlimited solubility between the components, 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 experience polymorphic transformations.

Mechanical mixtures are formed if the elements that make up the alloy, during solidification from the liquid state, do not dissolve in each other and do not interact. The structure of the mixture is a heterogeneous body. On the thin section, crystallites of various components forming a mechanical mixture are visible. Chemical analysis also determines various components. There are two types of crystal lattices.

Solid solutions- phases in which one of the components (solvent) retains its crystal lattice, while the atoms of other (dissolved) components are located in its lattice, distorting it. Chemical analysis solid solution shows the presence of two elements, and X-ray diffraction - one type of solvent lattice. On structure - homogeneous grains. If both components have the same type of crystal lattices, and their atomic diameters differ by no more than 8 - 15%, then unlimited solubility is possible (for example, gold and silver).

Chemical compounds formed when the elements that make up an alloy interact with each other. Structurally, they are homogeneous solids. The properties of chemical compounds differ from the properties of the elements that form them. They have a constant melting point. The crystal lattice of a chemical compound differs from the lattices of the initial components. In a chemical compound, a certain ratio of atoms of elements is preserved, i.e. There is a chemical formula for the compound.

Diagram of the state of the "iron-carbon" system

Iron and its alloys with carbon

Polymorphism - the property of a substance or material to change its crystal lattice with a change in temperature, Crystalline forms of α-Fe and ... Carbon is a non-metallic element. It occurs in nature in the form of two ... Under normal conditions, carbon is in the form of a modification of graphite with a hexagonal layered lattice. Modification…

Become

Become- iron-carbon alloys containing up to 2.14% carbon. In addition, the composition of the alloy usually includes manganese, silicon, sulfur and phosphorus. Some elements can be introduced specifically to improve physical and chemical properties (alloying elements).

By structure have been 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. C).

Dot D - eutectoid point(when austenite is cooled, a mechanical mixture of ferrite and cementite is formed). The eutectoid transformation does not occur from a liquid, but from a solid solution.

Depending on the chemical composition, carbon steel and alloy steel are distinguished. In its turn carbon steels can 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% alloying elements;

3) high-alloyed - contain over 10% alloying elements.

By appointment steels are:

1) structural, intended for body and machine-building products;

2) tool, 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 e.g. stainless, heat-resistant or heat-resistant steels.

Depending on the content of harmful impurities(sulfur and phosphorus) steels are divided into:

1. Steel 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. Particularly high quality, up to 0.025% phosphorus and up to 0.0] 5% sulfur.

Degree of oxygen removal from steel, i.e. according to the degree of its deoxidation, they distinguish:

1) calm steels, i.e. fully deoxidized, are indicated by the letters "sp" at the end of the brand;

2) boiling steel - slightly deoxidized, marked with the letters "kp";

3) semi-quiet steels, occupying an intermediate position between the two previous ones; denoted by the letters "ps".

Depending on the normalized indicators (tensile strength σ, relative elongation δ%, yield strength δt, cold bending), the steel of each group is divided into categories, which are indicated by Arabic numerals.

Standard quality steel denoted by the letters "St" and conditional brand number (from 0 to 6) depending on the chemical composition and mechanical properties. The higher the carbon content and strength properties of steel, the higher its number. To indicate the category of steel, a number is added to the brand designation at the end of the corresponding category, the first category is usually not indicated.

For example: St1kp2 - carbon steel of ordinary quality, boiling, grade No. 1, second category, supplied to consumers in terms of mechanical properties (group A).

quality steels mark as follows: at the beginning of the brand indicate the carbon content in hundredths of a percent for steels,

For example: 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 denoted by Russian letters: A - nitrogen, K - cobalt, T - titanium, B - niobium, M - molybdenum, F - vanadium, V - tungsten, H - nickel, X - chromium, G - manganese, P - phosphorus, D - copper, C - silicon.

If there is a number after the letter denoting the alloying element, then it indicates the content of this element as a percentage. If there is no number, then the steel contains 0.8 - 1.5% of the alloying element.

For example: 14G2 - low-alloyed quality steel, calm, contains approximately 14% carbon and up to 2.0% manganese.

OZKh16N15MZB - high-quality high-alloy 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 high-quality steel grade 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 the dash, the letter "Sh".

For example: U8A - high-quality carbon tool steel containing 0.8% carbon;

ZOHGS-Sh is a particularly high-quality medium-alloy steel containing 0.30% carbon and 0.8 to 1.5% chromium, manganese and silicon each.

Separate 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 number following it indicates the percentage of tungsten in it (P18).

Free-cutting 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 iron-carbon alloys containing more than 2.14% carbon. They contain the same impurities as steel, but in greater quantities.

Cast irons, unlike steels, complete crystallization with the formation of eutectics, have low plastic deformation capacity and high casting properties.

Depending on the state of the carbon in cast iron, distinguish:

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 irons).

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) hypoeutectic - carbon content up to 4.3%. The structure consists of perlite, secondary cementite and ledeburite;

2) eutectic - carbon content 4.3%. The structure consists of ledeburite;

3) hypereutectic - the carbon content is more than 4.3%. The structure consists 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 free carbon in the form of lamellar graphite. Under a microscope, graphite will appear as dark curved bands against a light background. Compared to a metal base, graphite has low strength. The places of its occurrence can be considered as discontinuities. Gray cast iron has low performance mechanical properties in tensile tests. However, gray cast iron also has a number of advantages: it allows you to get cheap casting, it has a good one. machinability, high damping properties.

Gray cast iron is marked with two letters SCH and two numbers corresponding to the minimum value of tensile strength in MPa.

For example: SCH10 - gray cast iron with a tensile strength of 100 MPa.

As graphite inclusions round off, their negative role as cuts in the metal base decreases, and the mechanical properties of cast irons increase. The rounded shape of graphite is achieved by modification. When used as a modifier of magnesium in an amount of up to 0.5%, ductile iron is obtained.

Ductile iron contains carbon in the free state in the form of spherical inclusions of graphite. Under the microscope, rounded dark grains of different sizes are observed on 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 magnitude of the temporary resistance.

For example: VCh 35 - high-strength cast iron with a tensile strength of 350 MPa.

malleable iron contains free carbon in the form of flake-shaped graphite. Ductile iron is obtained from white iron by graphitization annealing (long-term annealing at 1000°C). Under the microscope, a flocculent phase is observed on 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 example: 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 cast iron.

graphitization The process of graphite separation during crystallization or cooling of iron-carbon alloys is called. Graphitization is a diffusion process and proceeds slowly. The graphitization process consists of several stages:

1) formation of centers, graphitisation;

2) diffusion of carbon atoms to graphitization centers;

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 molding 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 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 state diagram given in the theoretical part.

3. Using samples-microsections of cast irons and an auxiliary album with photographs, study and graphically depict their structure. Determine the type of cast iron, the shape of graphite inclusions, the type of metal base. For white cast irons, determine the carbon content. Determine the phase composition of white cast irons from the state diagram.

4. Study 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 done, formulate conclusions.

Laboratory work No. 2,

STUDY OF MECHANICAL PROPERTIES

STRUCTURAL MATERIALS

Goal of the work: study the mechanical properties of structural materials and methods for evaluating 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 environment. The purpose of mechanical testing of materials is to determine precisely those or other properties or their combination, which will most fully characterize the reliability of the corresponding products under specified service conditions. The combination of such 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, which are often determined 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. Evaluation 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 property evaluation criteria 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 fracture under load;

2) plastic- the ability of the material to irreversibly change the shape and size without destruction under the action of a load;

3) fragility- the ability of the material to break down without protective absorption of energy;

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 dimensions after the load is removed;

6) hardness- the ability of a material to resist the penetration of another body into it in the surface layer.

Stretch Chart

The construction of a tensile diagram is the main task of tensile tests. For these tests, cylindrical specimens are used from ... The OA zone is called the elastic zone (after removing the load Rpts, 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.

Benefits of hardness testing

2. Measurement of hardness according to the execution technique is much simpler than determination of strength (does not require special samples, it is performed ... 3. Measurement of hardness does not entail the destruction of the part being tested and ... 4. Hardness can be measured on parts of small thickness, as well as in thin layers.

Determination of hardness on the Mohs scale

with glass, knife blade, etc., as shown in Table. 2.1. Table 2.1

experimental part

1. Tensile testing.

1.1. Get cylindrical specimens of steel tested in tension.

1.2. Using a caliper, make the necessary measurements of the lengths and diameters of the samples. Enter the data in Table 2.2.

Table 2.2

1.3. Determine the main mechanical characteristics, namely the tensile strength of the material, relative elongation and relative contraction according to the formulas given in the theoretical part of the work.

1.4. Construct a tensile diagram of steel images in the P-Δl coordinates.

1.5. Familiarize yourself with the tensile diagrams of various structural materials issued by the teacher, highlight the main zones, determine the mechanical characteristics.

2. Determination of the hardness of materials.

2.1. Brinell hardness determination:

a) the test specimen 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 table, remove the sample;

d) Using a microscope, measure the diameter of the resulting print and calculate the Brinell hardness.

2.2. Vickers hardness determination:

a) determine the length of the diagonals of the imprint on the sample installed on the microscope stage;

2.3. Study of the effect of carbon content in steel on its hardness;

a) measure the diameters of the prints of the obtained samples for steels ST20, ST45, U8;

b) determine the Brinell hardness values ​​using 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.

Lab #3

STUDYING THE PROCESS OF CRYSTALLIZATION OF MATERIALS

Goal of the work: to study the features of the process of crystallization of materials on 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 point, crystallization point, boiling point, or sublimation point.

Solid crystalline bodies have a regular structure, in which atoms and ions are located at 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 extend 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 exhibit the ability to grow.

As the temperature of the solid increases, the mobility of atoms at the lattice sites increases, the amplitude of oscillations also increases when

a certain temperature, called the melting point, the lattice collapses with the formation of a liquid phase.

The opposite picture is observed during cooling of the liquid (melt) and its subsequent solidification. 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. When the "melting-solidification" temperature is reached, a crystal lattice is formed again, and the metal passes into a solid state. The transition of a metal from a liquid state to a solid state at a certain temperature is called crystallization.

Crystalline bodies are characterized anisotropy- dependence of properties on the direction. Amorphous bodies (e.g. glass) are isotropic- their properties do not depend on the direction.

Let us consider the thermodynamic conditions of crystallization. The energy state of any system is characterized by a certain amount of internal energy, which is made up of the energy of the movement of molecules, atoms, etc. Free energy is such a component of internal energy, which under isothermal conditions can be converted into work. The value of free energy changes with a change in temperature, melting, polymorphic transformations, etc.

According to the second law of thermodynamics, any system tends to the minimum value of free energy. Any spontaneously current process goes on only if the new state is more stable, i.e. has less 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. The metal solidifies if the solid state has less free energy, and melts if the liquid state has less free energy. The change in the free energy of the liquid and solid states with a change in temperature is shown in fig. 3.1. Temperature changes in free energy are different for liquid and solid states of matter.

Rice. 3.1. Thermodynamic condition of crystallization

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 supercooling. The temperature at which crystallization occurs is called actual crystallization temperature T cr. The difference between theoretical and actual crystallization temperatures is called degree of hypothermia:ΔT \u003d T 0 - T cr. The greater the degree of supercooling ΔT, the greater the difference in free energies ΔF, the more intense the crystallization will be.

Just as solidification requires subcooling to the actual crystallization temperature, melting requires overheating to reach the actual melting temperature.

The mechanism of the crystallization process

1) nucleation of crystallization centers; 2) 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 heat removal that occurs due to cooling is compensated by heat ...

The structure of an ingot of calm steel

The diagram of the structure of a quiet steel ingot is shown in fig. 3.7. The structure of the ingot consists of three zones: the outer fine-grained zone 1, the columnar zone… Fig. 3.7. The structure of a metal ingot

experimental part

1. Conduct a thermal analysis of the metal.

1.1. Turn on the furnace in which the metal sample is placed.

1.2. Perform heating (melting) of the sample to the temperature specified by the laboratory assistant.

1.3. Take meter readings every 60 seconds. 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 meter readings 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

degree of hypothermia.

2. To study the process of crystallization on the example of metal salts.

2.1. Put 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 formation of zones, their number.

3. Based on the experimental results, formulate conclusions.

Lab #4

INVESTIGATION OF THERMAL PROPERTIES

STRUCTURAL 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, thermal expansion.

heat resistance refers to the ability of materials without damage and without acceptable deterioration of other practically important properties to reliably withstand the action of elevated temperature (short-term or for a time comparable to normal operating time). The value of heat resistance is estimated from the corresponding temperature values ​​at which changes in properties (for example, electrical properties for inorganic dielectrics) appeared. The heat resistance of organic dielectrics is often determined by the onset of mechanical deformations. If the deterioration of properties is detected only after prolonged exposure to elevated temperatures - due to slowly occurring chemical processes, then this is the so-called thermal aging of the material. In addition to the effect of temperature, the aging rate can be significantly affected by: an increase in air pressure, oxygen concentration,

various chemical reagents, etc.

For a number of brittle materials (glass, ceramics), resistance to abrupt changes temperature - thermal impulses. The ability to withstand heat changes is called heat resistance. With rapid heating or cooling of the surface of the material, 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 estimated by the number of heat cycles that a sample of material withstood without a noticeable change in properties.

As a result of the tests, the resistance of the material to thermal effects is determined, and this resistance may vary in different cases. For example, a material that easily withstands 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 and changes its properties upon rapid cooling. The elevated temperature test sometimes needs to be carried out with 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 the effects of 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 that are flexible and elastic at ordinary temperatures become very brittle and rigid at low temperatures, which leads to unreliable operation.

All solids are capable of conducting heat to some extent. Some are worse, others are better. Thermal conductivity is the property of materials to conduct heat from more heated parts of the body to less heated ones, leading to temperature equalization.

In principle, there are the following ways of transferring thermal energy in a substance:

1) radiation- All bodies, whatever their temperature, radiate energy. This may be a purely thermal phenomenon (thermal 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.

Fourier's basic law of heat conduction 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 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, tk. the degree of dispersion of thermal elastic waves is greater there. A decrease in thermal conductivity is also observed during the formation of solid solutions, because at the same time there are additional centers dispersion of thermal waves. In heterophase (multiphase) alloys, the thermal conductivity is the sum of the thermal conductivities of the formed phases. The thermal conductivity of 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 sizes and other factors. Heat capacity is the amount of heat corresponding to a change in the temperature of a unit 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 inherent in almost all materials.

Although the strength of the bonding forces in a solid body is very high, there are possibilities of movement elementary particles(atoms, ions). Both in amorphous bodies and in crystalline ones, the atoms vibrate around the center of equilibrium.

In this case, the oscillation amplitude increases with increasing temperature. Practice shows that the specific volume of most substances 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 oscillatory 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 potential energy systems from the interatomic distance. Any kind of chemical bond involves a balance of attractive and repulsive forces between atoms. When atoms approach each other, attractive forces dominate at first. The approach of atoms to a certain limit reduces the energy of the system, i.e. gives it 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 a decrease in the 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. Scheme of force interaction between

oppositely charged particles

The potential well is characterized by a strongly pronounced asymmetry. Let us assume that at a certain temperature an oscillating atom has a certain energy. In this case, it oscillates about the center, deviating alternately "left-right". Since displacements from the position

equilibrium must be the same, then an increase in the energy of the system causes a shift in the center of oscillation along the axis of the interatomic distance. Thus, the average distance between atoms increases as the temperature rises, which corresponds to the thermal expansion of the body.

Thus, the phenomenon of thermal expansion of solids is based on the anharmonicity of the oscillatory motion of its atoms, and the degree of deviation of thermal vibrations from the harmonic law, i.e. the value of the 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 nature of the bond, the potential well is characterized by a significant width and asymmetry. This fact determines a significant increase in the average interatomic distances when they are heated, or a significant thermal expansion of ionic compounds.

On the contrary, in substances with a predominantly covalent nature of the bond (borides, nitrides, carbides), the potential well has the shape of a pointed depression, and therefore the degree of its symmetry is higher. Therefore, the increase in the distance between atoms during heating is relatively small, which corresponds to their relatively small thermal expansion. Metals have, as a rule, increased thermal expansion, tk. the metallic bond is generally weaker than the ionic and covalent bonds. Finally, organic polymers are characterized by very large thermal expansion due to weak van der Waals forces acting between molecules, while strong covalent forces act within 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 with an infinitesimal change in temperature.

2. The temperature coefficient of volume expansion, which characterizes the three-dimensional expansion of a substance.

An important practical consequence is the need to use data on the thermal expansion coefficient obtained in a specific temperature range in which the material operates. Temperature coefficients cannot be compared
expansions of materials measured at different temperatures.

For isotropic materials (crystals with a cubic lattice, glasses), the CLTE is the same in all directions. Most crystalline substances, however, are anisotropic (the 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, the expansion of graphite along the layer is much less than perpendicular to it. For some similar materials with a strongly pronounced anisotropy, the LTEC value in one of the directions may even turn out to be negative. For example, cordierite 2MgO 2A1 2 O 3 5SiO 2, in which, during thermal expansion along one axis, expansion of the crystal is observed, and along the other axis, compression corresponding to the approach of the layers of the structure. This phenomenon is used in technology; in a field and a crystalline material, the chaotic distribution of crystals leads to the mutual orientation of their positive and negative expansion. The result is a material with a low TLEC value, characterized by a very high thermal stability. At the same time, significant stresses can arise in such materials at the grain boundaries, which affects their mechanical strength. For polyphase materials at the boundary of two contacting phases with different thermal expansion coefficients, the phase with a large expansion coefficient will be compressive and tensile stresses will act on the phase with a small thermal expansion coefficient (during heating). When cooled, the voltages change signs. If the critical stress values ​​are exceeded, cracks and even destruction of the material may occur.

Thus, the LTEC is a structurally sensitive property and sensitively reacts to changes in the structure of the material, for example, to the presence of polymorphic transformations in it. In this regard, inflections can be observed on the expansion curves of multiphase materials, their monotonic nature is violated.

If the expansion of the body in a given temperature range occurs uniformly, then graphically the expansion will be expressed as a straight line (Fig. 4.2.), And the average coefficient of linear expansion will be numerically equal to the tangent of the slope of this straight line to the temperature axis, related 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 not be expressed 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, it is necessary 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 value of thermal expansion of bodies during heating primarily depends on the nature of the given material, i.e. on its chemical and mineralogical composition, the structure of the spatial lattice, the strength of the chemical bond, etc. So,

The value of the thermal expansion coefficient of ceramics is determined primarily by the nature of the crystalline phase, glass - by the chemical composition, and ceramic glass - by the nature of the crystalline phase, the chemical composition of the residual vitreous 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 temperature, the expansion is proportional 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 occur, 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.

CLTE is a technical characteristic of the material and is calculated by the formula

where l 0 is the length of the body at the initial temperature T 0 ;

l t is the length of a body heated to a temperature T.

TCLE - change in length with a change in temperature by 1 degree, referred to the original length of the sample. Materials with a low thermal expansion coefficient are used as parts of high-precision instruments and equipment, which should not change dimensions when heated. When parts of the device are rigidly connected, for example, in a junction of metal with glass, it is necessary to choose materials with close values ​​of thermal expansion coefficient, 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 TCLE is also necessary for the layers of microcircuits subjected to temperature changes during technological operations or in the course of operation, otherwise the layers of the circuit may be destroyed.

The coefficient of thermal expansion also plays an important role in assessing the thermal stability of materials: the lower the thermal expansion coefficient, the higher the thermal stability.

There are metal alloys that do not obey the general laws of thermal properties. Such alloys are alloys of iron with nickel Re-M1. An alloy containing 36% nickel has a TCLE value close to zero and is called invar(lat. "unchanging").

Engineers take advantage of another thermal property, namely thermal modulus of elasticity(TKMU). 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-Ni 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 maximum TKMU. The selection of a certain chemical composition makes it possible to develop alloys whose TCMC are practically independent of temperature. These alloys are called elinvars.

Steels with a certain thermal expansion are used to manufacture thermobimetals when a layer with low thermal expansion (passive layer) is securely bonded by rolling to another layer with higher thermal expansion (active layer). Bimetallic plates are used as a temperature controller in instrumentation.

Heating of such a plate leads to its curvature, which allows to close the electrical circuit. The main property of thermobimetals is thermal sensitivity- the ability to bend with temperature changes.

Description of the quartz dilatometer used to measure the temperature 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. Get acquainted with the device of the dilatometer.

2. Place the tube with the bronze sample in the tube furnace.

3. Switch on the oven and the combined reading instrument.

4. Set the indicator to zero.

5. At regular intervals (for example, after 20°C), 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 dyne of the sample;

α q - correction for the expansion of quartz.

8. Construct and explain the graphic dependence of the elongation of the sample 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 g -1 , α tin = 230 ·10 -7 g -1 .

10. Familiarize yourself with the expansion curves for non-metallic materials, identify characteristic zones, explain the processes that occur in materials when heated.

11. Based on the results of the work, formulate conclusions.

Lab #5

METHODS FOR STUDYING POROUS COMPOSITE MATERIALS

Goal of the work: Familiarize yourself with various porous materials and their manufacturing technology. Determine the water absorption of polymeric, composite and glass-ceramic materials and make a comparative analysis of the results obtained.

Theoretical part

All materials, to a greater or lesser extent, have water absorption, i.e. ability to absorb V moisture from the environment and moisture permeability, those. the ability to pass water through. Atmospheric air always contains some water vapor.

The water absorption of the material is significantly affected 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 materials, have a high water absorption. Determination of water absorption by increasing the mass of the wetted sample gives some idea of ​​the ability of the material to absorb moisture.

Any porous structural material (metal, ceramic, glass-ceramic or polymer) is, as a rule, a combination of a solid substance 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. For example, the mechanical strength of ceramics depends not only on the total porosity, but also on the size of the pores and 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 nature of the distribution of pores largely determine the slag resistance of the furnace lining; porosity affects the thermal conductivity of materials.

Pores in materials have various shapes, outlines, and can be unevenly distributed over the volume; therefore, it is extremely difficult to obtain a complete characterization of porosity, even when using modern porosity meters. Despite the variety of forms, pores can be divided into:

1. Closed pores- inaccessible to the penetration of liquids and gases.

2. open- pores available for penetration.

Open pores, in turn, are divided into:

1) dead ends- 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 determined primarily by channel-forming pores in the presence of pressure drops at their open ends. Porosity and permeability are important texture characteristics for all types of engineering materials.

Since direct methods for measuring the porosity of materials are extremely complex, this indicator is often estimated by determining other properties that are directly dependent on porosity. These indicators include the density of the material and water absorption.

Let's look at some definitions.

True Density- the ratio of the mass of the material to its volume, excluding pores.

Apparent density- this 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, it is possible to evaluate the overall, open and closed porosity of the ceramic.

True (total) porosity- the total volume of all open and closed pores, expressed as a % of 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- this 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 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, it is denoted by 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 ...

Plastic classification

Plastics can be classified according to various criteria, such as composition, heat and solvents, etc.

Composition plastics are divided into:

1) unfilled. They are pure resin.

2) filled (composite). They contain, in addition to resin, fillers, plasticizers, stabilizers, hardeners and special additives.

Fillers 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 plastics and degrades electrical performance.

plasticizers(glycerin, castor or paraffin oil) is introduced in an amount of 10-20% to reduce brittleness and improve awn formability.

Stabilizers(soot, sulfur compounds, phenols) are introduced 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 operational 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 to connect polymer molecules by chemical bonds.

Special additives- lubricants, dyes, to reduce static charges, to reduce flammability, to protect against mold.

In the manufacture of foam and foam plastics, blowing agents are added - substances that soften when heated, releasing a large amount of gases that foam the resin.

Relative to heating and solvent plastics are divided into thermoplastic and thermoset.

Thermoplastic polymers(thermoplastics) - polymers that can repeatedly soften when heated and harden when cooled without changing their properties. In these polymers, weak van der Waaps forces act between molecules, and there are no chemical bonds. Thermoplastics also have solubility in solvents.

Thermoset polymers(thermoplastics), when heated to a certain temperature, melt and as a result of chemical reactions at the same temperature, when cooled, they harden (as they say, “bake”), turning into a hard, non-melting and insoluble substance. In this case, along with weak van der Waals forces, there are strong chemical bonds between molecules, called transverse ones. Their occurrence is the essence of the polymer curing process.

According to the decreasing effect of the filler plastics are divided into the following types:

1) with sheet filler (getinaks, textolite, fiberglass, wood-laminated plastic);

2) with fiber filling(fiber, asbestos fiber, fiberglass);

3) with powder filling(phenolic, amino,

epoxy press powders);

4) without filler(polyethylene, polystyrene);

5) with gas-air filler(foams).

Getinaks consists of two or more layers of strong, heat-resistant, impregnating paper, treated with a thermosetting phenol-formaldehyde resole type resin (bakelite). In order to increase the heat resistance, organosilicon substances are additionally introduced into some grades of getinax, and epoxy resins are added to increase the adhesive ability. Getinaks is a cheap material used in REA for the manufacture of various kinds of flat electrical insulating parts and printed circuit board bases.

Heat resistance of getinaks - 135°C. 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 getinaks, with bakelite. It is easier to process than getinaks, has higher water resistance, compressive strength and impact strength. Textolite is 5-6 times more expensive than getinaks. Heat resistance 150°С.

Fiberglass- a material consisting of two or more layers of alkali-free glass fabric impregnated with various thermosetting resins.

Fiberglass, in comparison with getinax and textolite, has increased moisture resistance, heat resistance and better electrical and mechanical parameters, but is less mechanically processed. Fiberglass has a good damping ability (the ability to dampen vibrations) and is superior in this respect to steel and titanium alloys. In terms of thermal expansion, it is close to steels. Heat resistance - 185°С. Fiberglass is widely used because it combines light weight, high strength, heat resistance and good electrical properties.

Wood-laminated plastic - a material with a filler in the form of sawdust or veneer.

Sheet foil plastics have a special purpose and are used for the manufacture of printed circuit boards. They are laminated plastic lined on one or both sides with electrolytic copper foil.

This method of obtaining foil provides a uniform composition and a rough surface on one side, which improves the adhesion of the foil to the dielectric during gluing. 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 by keeping the sample in water for 24 hours at room temperature (or by boiling for 30 minutes).

Table 5.1.

Properties of plastics

2. Plastics are resistant to long-term action of industrial aggressive environments and are used for the manufacture of protective coatings on metals. ... 3. Under the influence of the environment, plastics age slowly, that is ... 4. Most polymers can work for a long time only at temperatures below 100 ° C. Above this temperature...

Porous ceramic and glass-ceramic materials

1) obtaining initial powders, 2) consolidation of powders, i.e. production of compact materials; 3) processing and control of products.

Porous metal 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. boiling 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. Record 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 dimensions of the samples required to calculate the volume using a caliper.

2.2. Place the samples in a beaker, bring to a boil and hold at the boiling temperature for 60 minutes.

2.3. Remove samples from the beaker and weigh. Attention! Samples should not be thoroughly blotted as they will water will be removed from relatively large holes.

2.4. Determine the water absorption of each sample using the formula above.

2.5. Determine the apparent density of the samples using the formula

2.6. Calculate the apparent (open) porosity P to:

2.7. Record the results of the calculations in Table 5.3.

Table 5.3

3. Based on the experimental results, conduct a comparative analysis and formulate conclusions.

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