Superhard material design. Superhard materials Superhard materials composition properties grade application

High hardness materials are used mainly in mechanisms subject to abrasive wear.

Of the simple substances, only diamonds and boron have great hardness.

The overwhelming majority of substances of high hardness are refractory chemical compounds (carbides, nitrides, borides, silicides).

Due to the high fragility of solid joints and the difficulty of processing them, the manufacture of parts from them in most cases is impractical or economically unprofitable. Their main area of application is solid constituents. composite materials and coatings applied in a variety of ways.

Superhard materials

These include cubic modifications of carbon (diamond) and boron nitride.

Synthetic diamonds in the form of powders are used for the preparation of abrasive tools and abrasive crust, in the form of dense polycrystalline formations (Ballas, Carbonado) for the production of abrasive tools, cutters, dies.

By sintering a mixture of micropowders of synthetic and natural diamonds, dense polycrystalline diamond formations - CB and Dismit - are obtained.

Diamonds of the SV brand are used for drill bits and bits, as well as for cutting non-metallic materials.

Dismit is used for the manufacture of mining tools, cutting tools (cutters, drills and others) used for processing non-ferrous metals and alloys, plastics, fiberglass.

Cubic boron nitride

Obtained only synthetically from the hexagonal modification. It is mainly used for the manufacture of abrasive tools. In terms of hardness, it is inferior to diamond, but significantly surpasses it in heat resistance.

In the USA, cubic boron nitride is produced under the name Borazon, in the CIS - Elbor and Cubonite. Their brands, respectively, LO and KO of normal strength and LR and KR - increased.

Varieties of polycrystalline material based on Elbor and Cubonite - Elbor-R, Geksanit - R, ISMIT, PNTB, COMPOSIT and others ... are produced in the form of plates of various shapes. They are used to make metal-cutting tools used in the processing of hard-to-machine hardened steels, cast irons and alloys with a hardness of HRC> 40. The durability of such a tool is 10 ... 20 times higher than that of a carbide tool, the productivity increases 2 ... 4 times.

Superhard materials

Superhard materials- a group of substances with the highest hardness, which includes materials whose hardness and wear resistance exceeds the hardness and wear resistance of hard alloys based on tungsten and titanium carbides with a cobalt carbide bond titanium alloys on a nickel-molybdenum bond. Widely used superhard materials: alumina, zirconium oxide, silicon carbide, boron carbide, borazon, rhenium diboride, diamond. Superhard materials are often used as abrasive materials.

In recent years, close attention modern industry is aimed at finding new types of superhard materials and assimilation of such materials as carbon nitride, boron-carbon-silicon alloy, silicon nitride, titanium carbide-scandium carbide alloy, alloys of borides and carbides of the titanium subgroup with lanthanide carbides and borides.

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See what "Superhard materials" is in other dictionaries:

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Books

Instrumental materials in mechanical engineering: Textbook. Grif of the Ministry of Defense of the Russian Federation, Adaskin AM .. The textbook presents materials for the manufacture of cutting, stamping, fitting and assembly, auxiliary, control and measuring tools: instrumental, high-speed and ...

What materials are considered superhard? What is the range of their application? Are there materials harder than diamond? Professor, PhD in Crystallography Artem Oganov talks about this.

Superhard materials are materials that have a hardness greater than 40 gigapascals. Hardness is a property traditionally measured by scratching. If one material scratches another, it is considered to have higher hardness. This is relative hardness; it does not have rigid quantitative characteristics. Strict quantitative characteristics of hardness are determined by a pressure test. When you take a pyramid, usually made of diamond, apply some force and press the pyramid against the surface of your test material, measure the pressure, measure the area of the indentation, a correction factor is applied, and this value will be the hardness of your material. It has the dimension of pressure, since it is force divided by area, therefore gigapascals (GPa).

40 GPa is the hardness of cubic polycrystalline boron nitride. This is a classic superhard material that is widely used. The hardest material known to mankind so far is diamond. For a long time, there have been attempts, which do not stop even now, to discover a material harder than diamond. So far, these attempts have not been successful.

Why do you need superhard materials? The number of superhard materials is small, about ten, maybe fifteen materials known today. First, superhard materials can be used in cutting, polishing, grinding, drilling. For tasks related to machine tool construction, jewelry, stone processing, mining, drilling, and so on, all this requires superhard materials.

Diamond is the hardest material, but it is not the most optimal material. The fact is that a diamond, firstly, is fragile, and secondly, a diamond burns in an oxygen atmosphere. Imagine a drill that heats up to high temperatures in an oxygen atmosphere. Diamond, being elemental carbon, will burn. And besides, you can't cut steel with a diamond. Why? Because carbon reacts with iron to form iron carbide, which means that your diamond will simply dissolve in steel at a high enough temperature, and therefore you need to look for some other materials. Besides, diamond is of course quite expensive, even synthetic diamond is not a cheap enough material.

Moreover, superhard materials can still be useful in body armor and other protective military devices. In particular, a material such as boron carbide is widely used, which is also superhard and fairly light. Such is the range of applications for superhard materials.

It is known that superhard materials are formed in substances with a strong covalent bond. The ionic bond lowers the hardness. The metal bond also lowers the hardness. The bonds should be strong, directed, that is, covalent, and as short as possible. The density of a substance should also be as high as possible, density in terms of the number of atoms per unit volume. And, if possible, the symmetry of the substance should also be very high so that the substance is equally strong in this direction, and in this, and in this. Otherwise, the story will be the same as in graphite, where the bonds are very strong, but only in two directions, and in the third direction, the bonds between the layers are extremely weak, as a result, the substance is also soft.

Many institutes, many laboratories around the world are engaged in the synthesis and development of superhard materials. In particular, these are the Institute for High Pressure Physics in the Moscow Region, the Institute for Superhard and New Carbon Materials in the Moscow Region, the Institute for Superhard Materials in Kiev and a number of laboratories in the West. Active development in this area began, I think, in the 50s, when artificial diamonds were first obtained in Sweden and America. At first, these developments were secret, but soon enough the synthesis of artificial diamonds was also established in the Soviet Union, thanks to the work of researchers from the Institute of High Pressure Physics and the Institute of Superhard Materials.

There have been various attempts to create materials harder than diamond. The first attempt was based on fullerenes. are soccer-ball-like molecules, hollow molecules, round or somewhat elongated. The bonds between these molecules are very weak. That is, it is a molecular crystal composed of healthy molecules. But the bonds between the molecules are weak, van der Waals. If this kind of crystal is squeezed, then bonds will begin to form between the molecules, between these balls, and the structure will turn into a three-dimensionally connected covalent very solid structure. This material was named tisnumite in honor of the Technological Institute for Superhard and New Carbon Materials. It was assumed that this material has a higher hardness than diamond, but further research has shown that this is most likely not the case.

There were proposals and a fairly active discussion about the fact that carbon nitrides can be harder than diamond, but, despite active discussion and active research, so far such material has not been presented to the world.

Was enough fun job Chinese researchers, in which they suggested on the basis of theoretical calculations that another modification of carbon is similar to diamond in many ways, but slightly different from it, and is called lonsdaleite. According to this work, lonsdaleite is harder than diamond. Lonsdaleite is an interesting material, thin lamellas of this material have been found in shock-compressed diamond. This mineral was named after the famous woman Kathleen Lonsdale, the great British crystallographer, who lived in the 50s and 70s of the XX century. She had an extremely interesting biography, she even had a chance to sit in prison when she refused to put out fires during the Second World War. She was a Quaker religion, and Quakers were forbidden to do anything related to the war, even to put out fires. And for this they put her in a paddy wagon. But nevertheless, everything was fine with her, she was the president of the International Union of Crystallographers, and this mineral was named in her honor.

Lonsdaleite, judging by all available experimental and theoretical data, is still softer than diamond. If you look at the work of these Chinese researchers, you can see that even according to their calculations, lonsdaleite is softer than diamond. But somehow the conclusion was made contrary to their own results.

Thus, it turns out that there is no real candidate for removing a diamond from the position of the hardest substance itself. But nevertheless, the question is worth working it out. Still, many laboratories are still trying to create such a material. Using our method of predicting crystal structures, we decided to ask this question. And the task can be formulated as follows: you are not looking for a substance that has maximum stability, but a substance that has maximum hardness. You specify a range of chemical compositions, for example, from pure carbon to pure nitrogen, and everything in between, all possible carbon nitrides are included in your calculation, and you are evolutionarily trying to find more and more solid compositions and structures.

The hardest substance in this system is the same diamond, and adding nitrogen to carbon does not improve anything in this system.

Thus, the hypothesis of carbon nitrides as substances harder than diamond can be buried.

We tried everything else that was suggested in the literature, different shapes carbon and so on - in all cases, the diamond always won. So it looks like the diamond cannot be removed from this pedestal. But it is possible to invent new materials that are preferable to diamond in a number of other respects, for example, in terms of fracture toughness or in terms of chemical resistance.

For example, elemental boron. We have discovered a structure, a new boron modification. We published this article in 2009, and it caused a tremendous response. The structure is obtained by applying low pressure to ordinary boron and heating it to high temperatures. We called this form gamma-boron, and it turned out that it contains a partial ionic chemical bond. In fact, this is something that will somewhat lower the hardness, but due to its high density, this modification still turns out to be the hardest known modification of boron, its hardness is about 50 GPa. The synthesis pressures are small, and therefore, in principle, one can even think about its synthesis in sufficiently large volumes.

We predicted a number of other superhard phases, such as phases in the "tungsten - boron", "chromium - boron" system, and so on. All these phases are superhard, but their hardness still belongs to the lower part of this range. They are closer to the 40 GPa mark than to the 90–100 GPa mark, which corresponds to the hardness of diamond.

But the search continues, we do not despair, and it is quite possible that we or our other colleagues working on this topic around the world will be able to invent a material that can be synthesized at low pressures and which will be close to diamond in hardness. Something in this area has already been done by us and other colleagues. But how to apply this technologically is not yet entirely clear.

I'll tell you about new form carbon, which was actually produced experimentally back in 1963 by American researchers. The experiment was conceptually simple enough: they took carbon in the form of graphite and squeezed it at room temperature. The fact is that a diamond cannot be obtained this way; a diamond requires strong heating. Instead of diamond, their experiments formed a transparent superhard non-metallic phase, but nevertheless it was not a diamond. And this did not agree with the characteristics of any of the known forms of carbon. What's the matter, what is this structure?

Quite by accident, while studying various structures of carbon, we came across one structure that was only slightly inferior to diamond in terms of stability. Only three years after we saw this structure, looked at it, even published somewhere between the lines, it dawned on us that it would be nice to compare the properties of this structure with what was published by all those researchers since 1963 and right up to the most recent years. And it turned out that there is a complete coincidence. We were happy, we quickly published an article in one of the most prestigious magazines, The Physical Review Letters, and a year later an article in the same journal was published by American and Japanese researchers who found that a completely different structure of carbon also describes the same experimental data. The problem is that the experimental data were of poor enough resolution. So who's right?

Soon, Swiss and Chinese researchers proposed a number of modifications. And in the end, a Chinese researcher published about forty carbon structures, most of which also describe the same experimental data. He promised me that if he was not too lazy, he would offer about a hundred more structures. So which structure is correct?

To do this, we had to investigate the kinetics of the transformation of graphite into various structures of carbon, and it turned out that we were very lucky. It turned out that our structure is the most preferable from the point of view of transformation kinetics.

A month after the publication of our article, an experimental work came out in which the experimenters made the most accurate experiment with data of much better resolution than before, and it really turned out that of all those dozens of published structures, only one structure explains the experimental data - this is still our structure. This new material we named M-carbon, since its symmetry is monoclinic, from the first letter M.

This material is only slightly inferior in hardness to diamond, but whether there is any property in which it surpasses diamond is still unclear.

Until now, it can be said to be a “thing in itself”. We continue to search and hope that we will be able to invent a material that, while not inferior to diamond in hardness, will significantly overtake it in all other characteristics.

One of the ways to improve the mechanical characteristics of substances is to nanostructure them. In particular, the hardness of the same diamond can be increased by creating diamond nanocomposites or diamond nanopolycrystals. In such cases, the hardness can be increased even 2 times. And this was done by Japanese researchers, and now you can see the products they produce, rather large, on the order of a cubic centimeter, diamond nanopolycrystals. The main problem with these nanopolycrystals is that they are so hard that it is nearly impossible to even grind them, and an entire laboratory grinds it for weeks.

In this way, you can both change the chemistry, change the structure of a substance in search of an improvement in its hardness and other characteristics, and change the dimension.

A significant reserve for increasing the productivity of cutting is the use of tools equipped with STM inserts based on polycrystalline diamonds, cubic and hexagonal boron nitride.

It is customary to call STM materials that have a Vickers hardness at 20 ° C above 35 hPa. The submicro-fine grain size of STM (some types) allows to provide a radius of rounding of edges of 0.3-3 microns when sharpening a tool, and due to the exceptionally high "hot hardness" (measured on samples heated to the appropriate temperature in a vacuum) and wear resistance, STM tools can be used at high and ultra-high cutting speeds. For example, a tool made of STM when cutting at speeds of 900-1200 m / min allows you to obtain the parameters of the roughness of the machined surface Ra<0,8-0,1 мкм. Это значительно меньшая шероховатость, чем шероховатость, полученная при шлифовании, и соизмерима с шероховатостью после притирки, суперфиниширования или алмазного выглаживания.

Currently, a large number of STM grades are produced based on dense modifications of boron nitride and diamond (Table 2.5).

Table 2.5

Characteristics of the physical and mechanical properties of superhard materials based on boron nitride and diamond (20 ° C)

Private label	r, g / cm 3	d compressed, hPa	d and, hPa	HV, hPa	E, hPa	TO 1C, mPa / m 2
Composite 01 * (Elbor-RM)	3,4	2,7	-			4,2
Composite 02 * (belbor)	6,5	-	-	-	-	-
Composite 05 *	4,3	2,2	0,47	18,8		6,7
Composite 09 * (PTNB)	-	3,4-4,9	1,0	-	-	-
Composite 10 * (hexanite)	3,4	2,6	1,0-1,2		-	3,8
Borazon *	3,48	-	-		-	-
Amborite *	-	-	0,57	40,5		-
ASB **	3,5-3,9	0,21-0,4	0,5-1,0	50-114	-	-
ASPK **	3,5-4,0	-	0,5-1,0	92-150	-	-
SVBN **	3,34-3,46	8-10	-	70-100	-	-

The end of the table. 2.5

Carbonite **	3,2-3,4	4,42-5,88	-	39-44	-	-
Compax **	-	-	-		-	-
Megadimond **	3,1-3,48	-	-	-	-	-

* CTM based on boron nitride

** Private label on the basis of diamond

The properties of cubic boron nitride (CBN) are due to the purely covalent nature of the atomic bond with a high localization of valence electrons at the atoms. CBN is characterized by high chemical resistance, hardness, thermal stability at a temperature of 1450 ° C. This makes it possible to use ultra-high cutting speeds (up to 1200 m / min) for CBN tools. However, the relatively low strength ( s and »0.47-0.7 hPa) and the increased brittleness of the CBN make it possible to use the tool only for finishing workpieces from brittle, hard materials with a limited cross-section of the cut material and increased rigidity of the technological system. The use of CBN tools for machining high-strength cast irons, hardened steels (HRCe> 40) and some alloys allows 10-20 times the cutting speed of these materials with a carbide tool.

The blade tool, equipped with natural single crystals and synthetic polycrystals of diamonds, as well as cubic boron nitride, provides high-quality processing of parts made of non-ferrous metals and alloys, hardened steels and cast iron, non-metallic materials, hard alloy and mineral ceramics in conditions of serial, mass and automated production... This tool has a high durability, allows you to get high precision products without changeovers for a long time, which determines the effectiveness of its use on automatic lines and CNC machines. In some cases, the use of such a tool allows you to replace grinding operations with blade processing.

Used for manufacturing cutting tools natural diamonds (A) belong to the cut group, i.e. diamonds, which are given the required geometric shape and dimensions. Diamond and graphite by chemical composition are pure carbon and are only its different modifications, differing in the arrangement of atoms in the structural lattice. Graphite has a hexagonal (hexagonal) structural lattice with a distance between layers of 3.35 A. Carbon atoms are located in a layer along the vertices of regular hexagons. The distance between the atoms in the layer is 1.42 A; the centers of the hexagons remain empty. The mutual orientation of the layers is such that the three vertices of the hexagon of one layer are located above the centers of the hexagons of the next layer. As a result of this structure of graphite, the bonds between the carbon atoms in the layer are very strong, and between the layers, in mind long distance between them, very weak, which leads to easy exfoliation of graphite in this direction.

The diamond has a cubic crystal lattice containing 18 carbon atoms, of which 8 are located at the vertices of the cube, 6 are at the centers of the cube faces, and 4 are at the centers of 4 out of 8 cubes formed by dividing an elementary cubic cell by three mutually perpendicular planes. The crystal lattice constant of diamond is 3.57 A, and the shortest distance between atoms is 1.54 A. Each carbon atom in the diamond lattice is linked by common electrons to four equivalent atoms. Carbon atoms in diamond have extremely strong covalent bonds, which are responsible for its extremely high hardness and other features.

Diamond is anisotropic in hardness, which is due to the unequal distance between atoms in different directions and an unequal number of atoms contained in different planes. The property of anisotropy of diamond in terms of hardness is taken into account in the manufacture of single-crystal diamond tools.

Conditionally distinguish between "hard" and "soft" directions in diamond crystals. The diamond is easier to work in the soft directions, but wears out more than in the hard ones. When making tools, the diamond must be processed in the "soft" direction, and in the process of work, the crystal must be oriented so that the wear occurs in the "hard" direction. The directions in crystals are determined by their external shape and on special installations using X-rays or sound vibrations. Laboratory tests it was found that the accuracy of the orientation of the main cutting edge of the tool relative to the crystallographic axes has a more significant effect on the durability of the diamond tool than other parameters of the cutting process, including the elements of the cutting mode. The grinding performance of a single crystal of diamond, in the "hard" and "soft" directions, can differ by almost 100 times.

Diamond has the highest hardness of all minerals known in nature; on the Mohs scale, the diamond takes the highest, tenth place. The Vickers microhardness of diamond (measured by a diamond pyramid with an angle between opposite faces of 136 °) is approximately 100 hPa. Along with high hardness, diamond possesses high wear resistance and abrasive ability.

Diamond has an extremely high thermal conductivity. The coefficient of linear expansion of diamond is many times less than the coefficient of linear expansion of hard alloys. Therefore, tools with diamond crystals have low thermal deformations. The modulus of elasticity of diamond exceeds the modulus of elasticity of all known solids in nature.

One of the important properties of diamond is its low coefficient of friction. The disadvantage of diamond as a tool material is its relatively low heat resistance. In air, diamond burns at a temperature of 850-1000 ° C.

The limited reserves of natural diamonds, as well as their high cost, have necessitated the development of artificial diamond technologies. The conditions for the production of artificial diamonds are in the impact on the diamond-forming material containing carbon (graphite, soot, charcoal), a pressure of 60 thousand atmospheres at a temperature of 2000-3000 ° C, which ensures the mobility of carbon atoms and the possibility of restructuring the graphite structure into a diamond structure. The synthesis is carried out in high-strength vessels - autoclaves in the presence of chemical catalysts (iron, nickel, chromium, etc.). When producing diamonds without catalysts, a pressure of 215 thousand atmospheres and a temperature of over 3770 ° C are required.

Cubic boron nitride (CBN) is effective for machining hardened steels and ductile irons.

There are three options for technical processes for obtaining a private label:

Synthesis from hexagonal nitride, boron;

Synthesis from wurtzite-like boron nitride;

Sintering from cubic boron nitride powders with alloying additives.

According to the first variant of the technological process, Composite 01 (Elbor-R) * and Composite 02 (Belbor) are manufactured. Composite 01 is synthesized with a catalyst, while Composite 02 is synthesized without a catalyst. The end product in both cases is cubic boron nitride.

Composite 10 (Hexanit-R) and Composite 09 (PTNB) are obtained according to the second version of the technical process. Composite 10 is prepared by synthesis and sintering. The starting material is wurtzite-like boron nitride, the final material is a mixture of wurtzite-like and cubic boron nitride. Composite 09 is the result of synthesis from a mixture of wurtzite-like and cubic boron nitride, final product- cubic boron nitride.

According to the third variant of the technological process, Composite 05 is manufactured (sintering from CBN and Al 2 O 3 powders) and its modification - composite 05 I.

Polycrystals of all these brands differ in size and physical and mechanical properties.

Composites 01 and 02 have maximum microhardness (»75 hPa), but low strength (s and» 0.4-0.5 hPa); the diameter and height of the blanks in this case are about 4 mm, the weight is 0.8 carats. The presence of wurtzite in the initial and final materials increases the strength, but decreases the hardness of the resulting polycrystal

Composite 10 has a microhardness of 40-50 hPa, but its strength is higher than that of Composites 01 and 02 (s and »0.7-1 hPa). The diameter of the Composite 10 polycrystals is 4-6 mm, the height is 4-5 mm, and the weight is 1.5 carats.

Cubic boron nitride is superior in hardness to all materials except diamond; the lower hardness is mainly due to the fact that the lattice parameters of cubic boron nitride are somewhat larger than those of diamond. The heat resistance of CBN is higher than that of diamond; CBN does not lose its cutting properties up to a temperature of »1200 ° C. Exactly these unique properties, along with chemical inertness to iron-containing alloys and high wear resistance, predetermined the possibility of using CBN in processing hardened and high-strength steels, as well as cast irons with high cutting speeds.

Natural and synthetic minerals are widely used in mechanical engineering for the manufacture of cutting and abrasive tools. The most widely used natural minerals are diamond, quartz, corundum, and synthetic ones - diamonds, cubic boron nitride, electrocorundum, boron carbide, silicon carbide. In many respects, synthetic materials are superior to natural ones. The main properties of synthetic superhard materials (STM) used in cutting are shown in Table 2.18.

Table 2.18

Basic properties of synthetic superhard materials

Name of private label	Name	Hardness, HV, GPa	Heat resistance, ° С
Ballas (ASB)	Synthetic diamond
Carbonado (ASPK)	Synthetic diamond
	Synthetic diamond
Composite 01
Composite 02 (05)
Composite 03
Composite 09
Composite 10	Hexait-R
Composite KP1 (bullpen)

Natural, synthetic diamonds and cubic boron nitride CBN are used for blade processing. For abrasive - natural and synthetic diamonds, cubic boron nitride, corundum and electrocorundum, silicon carbide, boron carbide, aluminum oxide, chromium oxide, iron oxide, as well as some rocks.

Diamond belongs to natural superhard natural materials. The name "diamond" comes from the Arabic al-mas, which translates as "hardest", or the Greek adamas (adamas), which means "irresistible, indestructible, invincible." At the end of the 18th century. it was found that the diamond is composed of carbon. Diamonds are found in the form of separate well-defined crystals or in the form of an accumulation of crystal grains and numerous intergrown crystals (aggregates). The unit for measuring the size of a diamond is carat (from Arab, kirat), which is 0.2 g.

It should be noted that natural diamonds are rarely used in metalworking. As a rule, for these purposes, they use the board (thrown overboard) - this is the name for all diamonds that are not used for making jewelry. For the manufacture of cutting tools (cutters, drills), diamond crystals weighing 0.2-0.6 carats are used. Diamond powders are used to make diamond wheels. Diamond crystals are fixed in the holder by soldering with silver solder or by mechanical fastening.

When sharpening, the diamond is preliminarily removed from the rod and regrind in a technological holder on special machines using cast iron discs, caricatured with a mixture of diamond powder and olive oil.

Polycrystals of synthetic diamonds are produced as ballas according to TU 2-037-19-70 (ASBZ and ASB4 for the manufacture of smoothers and ASPK2 for cutters). They are polycrystalline formations up to 12 mm in size of tightly bound crystals with high strength and wear resistance.

Fields of private label application:

for diamonds (A) - processing of non-ferrous metals and their alloys, as well as wood, abrasive materials, plastics, hard alloys, glass, ceramics;
for CBN - processing of ferrous metals, raw and hardened, as well as special alloys based on nickel and cobalt.

Currently, the industry mainly uses synthetic A, obtained from carbon (in the form of graphite) when exposed to high pressure and temperature, while the hexagonal face-centered lattice of graphite transforms into a cubic face-centered lattice of diamond. The temperature and pressure required for structural transformations are determined from the graphite-diamond phase diagram.

Since boron and nitrogen are located on both sides of carbon in the periodic table, a compound of these elements can be obtained by an appropriate chemical reaction, i.e. boron nitride, which has a graphite-like hexagonal crystal lattice with approximately the same number of boron and nitrogen atoms, located alternately. Similar to graphite, hexagonal boron nitride (HDD) has a layered loose structure and can be converted into CBN. This process is described by the diameter of the state of the HDD - CBN. By adding special catalytic solvents (usually metal nitrides), the conversion rate increases, and the pressure and temperature of the process are reduced to 6 GPa and 1500 ° C, respectively. During the transformation, CBN crystals increase. individual crystals of CBN are sintered together in the contact zones and form a "polycrystalline" mass.

As a result of sintering, a CBN conglomerate is obtained, in which arbitrarily oriented anisotropic crystals are interconnected, forming an isotropic mass of large volume. Then, from this mass, plates for cutting tools, dies for drawing wire, tools for dressing grinding wheels, wear-resistant parts, etc. are obtained.

As a cutting material, diamond has high durability and low friction when paired with metal, which provides a high surface quality. Diamonds are used (natural and synthetic) for precision turning and boring of non-ferrous alloy parts. Diamonds are not used for processing carbon-containing metals (cast irons, steels), since due to the chemical affinity of the processed and tool materials, the diamond cutters are intensively worn out and the surface layer of the workpiece is carburized.

Boron nitride materials are crystalline cubic (CBN) or wurtzite-like (VNB) modification of the boron-nitrogen compound, synthesized using a technology similar to the production of synthetic diamonds. By varying technological factors, several different materials are obtained on this basis - elbor, cubonite, hexanite, etc. Polycrystals based on boron nitride are obtained up to 12 mm in size, they are used for processing steels and iron-based alloys.

In domestic production, materials based on boron nitride for abrasive tools are produced under the brand name Elbor, and for blade tools - composite.

The emergence of each qualitatively new group of tool materials is characterized primarily by a significant, abrupt increase in cutting speeds and, therefore, is always accompanied by profound changes in machine tool construction and machining technology.

Cutting speed is the most important factor in the intensification of cutting materials using tools made of synthetic superhard materials in conditions when the reserves of a significant increase in cutting speeds of traditional tool materials are practically exhausted.

At the same time, as recent studies show, cutting speed is also a very effective factor in solving the problem of chip breaking - one of the most difficult problems in metalworking.

At a high cutting speed, work is almost completely converted into heat and segmented chips are formed, in which the segments are separated by a fragile narrow bridge of highly deformed metal; in fact, short crushed shavings are formed. Automation of material processing processes with chip removal and further increase in cutting speeds are inseparable.

A sharp increase in cutting speed, all other things being equal, provide a corresponding increase in the minute feed of the tool, i.e., the productivity of the process, as well as a decrease in the cutting force, work hardening and roughness of the machined surface, i.e., the accuracy and quality of processing. It has been established, in addition, that with an increase in the cutting speed within certain limits, the reliability of the STM tool increases; this is fundamentally important when applied to automated equipment.

As a rule, part of the available cutting speed increase reserve when switching from carbide tools to STM tools is used to reduce the thickness of the cut layer. For example, with an increase in the milling speed of cast iron by 10 times, the minute feed can be increased not by 10, but by 4 times, with a corresponding decrease in the feed per revolution by 2.5 times. This gives an additional significant reduction in cutting force and surface roughness.

From the materials obtained by sintering diamond grains, polycrystals of SV, SHS, dismit, SVBN, carbonite are currently produced.

ASB polycrystals have a spherical shape with a diameter of about 6-6.5 mm, a clearly pronounced radial structure. Ballas crystals form a block structure and different sizes over the cross section of the sample: in the center they are smaller than on the periphery. Their value is in the range of 10-300 microns.

ASPK diamonds have the shape of a cylinder with a diameter of 2-4.5 mm, a height of 3-5 mm, their structure is also radially-radiant, but more finely formed and perfect. The grain sizes are smaller (up to 200 microns).

The structure of SV type diamonds is polycrystalline, two-phase. The total amount of impurities does not exceed 2%.

As the strength increases, diamond polycrystals are arranged as follows: ASB, ASPK, SV, dismit.

A diamond tool can be operated, unlike a composite tool, and on low speeds inherent carbide tools, providing a manifold increase in durability. When milling, the speeds can be increased by 1.5-2 times. The depth of cut in wood-based materials is determined by the width of the cutters or saws.

The efficiency of using SA in the processing of high-hardness materials can be illustrated by the example of turning hard alloys VK10, VK10S, VS15, VK20 with ASPC cutters. The productivity of such processing is ten times higher than the productivity of grinding while maintaining the required quality consistently.

Processed material	Cutting speed, V, m / min	Innings, S, mm / rev	Cutting depth, t, mm
Aluminum and aluminum alloys
Aluminum alloys (10-20% silicon)
Copper and copper alloys (bronzes, brass, babbits, etc.)
Various composites (plastics, plastics, fiberglass, carbon fiber, hard rubber)
Semi-sintered ceramics and cemented carbides
Sintered cemented carbide
Chipboard materials
Rocks (sandstone, granite)

High wear resistance is revealed by tools made of ASPK and ASB when turning abrasive materials, widespread high-silicon and copper alloys, fiberglass, plastic ceramics, press materials, etc. It is ten or more times higher than that of carbide.

Significant experience has been accumulated in turning and boring with ASPC cutters of billets made of aluminum alloys AL-2, AL-9, AL-25, AK-6, AK-9, AK-12M2, VKZhLS-2, titanium alloys VT6, VT22, VT8, VTZ -1, fiberglass, non-ferrous metals, wood.

ASB polycrystals are characterized by high efficiency when turning high-silicon aluminum alloy AK-21, AL-25, copper-based alloy L62, when processing LS59-1, bronze, fiberglass ST, SVAM, AG, etc.