The most effective use of diamond tools is in finishing and finishing operations when processing parts made of non-ferrous metals and their alloys, as well as non-metallic and composite materials. Diamond, as a tool material, has two significant drawbacks - relatively low heat resistance and diffusion dissolution in iron at high temperatures, which practically excludes the use of diamond tools when processing steels and alloys capable of forming carbides. At the same time, thanks to the very high thermal conductivity, the cutting edge of the blade is intensively cooled, making diamond tools suitable for working at high cutting speeds.

The types of diamond-based STMs existing in world practice are presented in Fig. 6.23.

Rice. 6.23 Ultra-hard materials for diamond-based blade tools

Monocrystalline diamond blade tools are used for processing radio ceramics, semiconductor materials, and high-precision processing of non-ferrous alloys. Monocrystalline diamond tools are characterized by record wear resistance and a minimum radius of rounding of the cutting edge, which ensures high quality of the machined surface. It should be taken into account that the cost of a single-crystal diamond blade tool is several times higher than the cost of a polycrystalline diamond tool. The advantages of instrumental polycrystalline diamonds (PCD, abroad PCD), in comparison with single-crystal diamonds, are associated with the arbitrary orientation of crystals in the working layer of cutting inserts, which ensures high uniformity in hardness and abrasion resistance in all directions with high strength values. From polycrystalline diamonds obtained on the basis of a phase transition, ASPC grades, which are obtained from graphite during synthesis in the presence of metal solvents, have become widespread for blade tools. ASPC grades are produced in the form of cylinders with a diameter of 2, 3 and 4 mm, and a length of up to 4 mm.

Of all types of PCD, the most common are diamond tools obtained by sintering diamond powders (size 1...30 microns) in the presence of a cobalt catalyst. An example would be fine-grained CMX850 or the universal brand CTM302 from ElementSix, inserts of various shapes from VNIIALMAZ, OJSC MPO VAI. Significant advantages in terms of the strength of the plates and the convenience of their fastening by soldering in the tool body are provided by two-layer plates with a diamond layer on a carbide substrate, also called ATP - diamond-carbide plates. For example, such plates of various sizes are produced abroad by Diamond Innovations under the brand name Compax. Element Six produces Sindite inserts with diamond layer thicknesses from 0.3 to 2.5 mm and various diamond grain sizes. A domestically produced two-layer SVBN is soldered onto the top of a standard-sized carbide plate. The composite class includes diamond-containing materials based on hard alloys, as well as compositions based on polycrystalline diamonds and hexagonal boron nitride. Of the diamond-hard alloy composites that have proven themselves in operation, it should be noted “Slavutich” (from natural diamonds) and “Tvesal” (from synthetic diamonds).

Diamond polycrystals obtained by chemical vapor deposition (CVD-diamond) represent a fundamentally new type of diamond-based STM. Compared to other types of polycrystalline diamonds, they are characterized by high purity, hardness and thermal conductivity, but lower strength. They represent thick films, and in fact - plates with a thickness of 0.3...2.0 mm (the most typical thickness is 0.5 mm), which, after growing, are peeled off from the substrate, cut with a laser and soldered to carbide inserts. When processing highly abrasive and hard materials, they have durability that is several times higher than other PCDs. According to ElementSix, which produces such PCDs under the general name CVDite, they are recommended for continuous turning of ceramics, hard alloys, and metal matrix compositions. Not used for processing steel. In recent years, publications have appeared on the industrial growth of single-crystal diamonds using CVD technology. Thus, we should expect this type of single crystal diamond tools to appear on the market in the near future.

CVD technology produces not only the diamond blade tools described above, but also diamond coatings on carbide and some ceramic tool materials. Since the process temperature is 600...1000 0 C, such coatings cannot be applied to steel tools. The thickness of coatings on tools, including complex-profile ones (drills, milling cutters, SMP), is 1...40 microns. Areas of rational use of diamond coatings are similar to CVD diamond tools.

Diamond coatings should be distinguished from diamond-like coatings. Diamond-LikeCoating (DLC) amorphous coatings consist of carbon atoms with both diamond and graphite-like bonds. Diamond-like coatings applied by physical vapor deposition (PVD) and plasma activated chemical vapor deposition (PACVD) have a thickness of 1...30 microns (usually about 5 microns) and are characterized by high hardness and a record low coefficient of friction. Since the process of applying such coatings is carried out at temperatures no higher than 300 0 C, they are also used to increase the durability of high-speed tools. The greatest effect from diamond-like coatings is achieved when processing copper, aluminum, titanium alloys, non-metallic materials and highly abrasive materials.

Superhard composites based on boron nitride. STM based on polycrystalline cubic boron nitride (PCBN in Russia and PCBN abroad), slightly inferior to diamond in hardness, are characterized by high heat resistance, resistance to cyclic exposure to high temperatures and, most importantly, weaker chemical interaction with iron, therefore the greatest efficiency of use BN-based tools occur when machining cast irons and steels, including high-hard ones.

Abroad, according to ISO 513, the division of PCBN grades is carried out according to the content of cubic boron nitride in the material: with a high (70...95%) BN content (index "H") and a relatively small amount of binder, and with a low (40...70 %) BN content (index "L"). For low content PCBN grades, TiCN ceramic bond is used. Grades with a high BN content are recommended for high-speed machining of all types of cast iron, including hardened and bleached, as well as turning of heat-resistant nickel alloys. Low BN content PCBNs have greater strength and are used primarily for machining hardened steels, including interrupted machining. Sumitomo Electric also produces ceramic-coated PCBN inserts (BNC type), which have increased resistance to high-speed machining of steels and provide high quality surface finishes.

In addition to homogeneous in structure, PCBN are produced in the form of two-layer plates with a carbide base (similar to PKA). Composite PCBN is produced by sintering a mixture of synthetic diamond powders and cubic or wurtzite boron nitride. In foreign countries, materials based on wurtzite boron nitride are not widely used.

Purpose of STM based on cubic boron nitride:

Composite 01 (Elbor R), Composite 02 (Belbor R) - fine and fine turning without impact and face milling of hardened steels and cast irons of any hardness, hard alloys with a binder content of more than 15%.

Composite 03 (Ismit) - finishing and semi-fine processing of hardened steels and cast irons of any hardness.

Composite 05, composite 05IT, composite KP3 - preliminary and final turning without impact of hardened steels up to 55HRC and gray cast iron with hardness 160...600HB, cutting depth up to 0.2...2 mm, face milling of cast iron.

Composite 06 - fine turning of hardened steels up to 63HRC.

Composite 10 (Hexanit R), composite KP3 - preliminary and final turning with and without impact, face milling of steels and cast irons of any hardness, hard alloys with a binder content of more than 15%, intermittent turning, processing of deposited parts. Cutting depth 0.05...0.7 mm.

Tomal 10, Composite 10D - rough, semi-rough and finishing turning and milling of cast iron of any hardness, turning and boring of steels and copper-based alloys, cutting on casting crust.

Composite 11 (Kiborit) - preliminary and final turning, including impact turning, of hardened steels and cast irons of any hardness, wear-resistant plasma surfacing, face milling of hardened steels and cast irons.

Abroad, blade tools based on PCBN are produced by ElementSix, Diamond Innovations, Sumitomo Electric Industries, Toshiba Tungalloy, Kyocera, NTK Cutting Tools, Ceram Tec, Kennametal, Seco Tools, Mitsubishi Carbide, Sandvik Coromant, ISM (Ukraine), Widia, Ssangyong Materials Corporation, etc.

The main area of ​​effective use of blade cutting tools made from STM is automated production based on CNC machines, multi-purpose machines, automatic lines, and special high-speed machines. Due to the increased sensitivity of STM tools to vibrations and shock loads, increased demands are placed on machines in terms of accuracy, vibration resistance and rigidity of the technological system. Various types of CBN (cubic boron nitride composites) are used to process hardened steels and cast iron, which have high hardness and strength. Composites show excellent performance during processing and provide good surface quality due to their chemical composition and modern sintering technology (Fig. 6.24).

Figure 6.24 – Typical images of the microstructure of a CBN-based composite

The use of STM tools makes it possible to increase processing productivity several times compared to carbide tools, while improving the quality of machined surfaces and eliminating the need for subsequent abrasive processing. The choice of optimal cutting speed is determined by the amount of allowance removed, equipment capabilities, feed, the presence of shock loads during the cutting process and many other factors (Fig. 6.25, 6.26).

Figure 6.26 – Areas of application of some grades of composites

Figure 6.26 – Example of processing hardened steels with STM tools

7 PRINCIPLES OF CONSTRUCTION OF TECHNOLOGICAL PROCESSES WHEN PROCESSING MATERIALS BY CUTTING.

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

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

40 GPa is the hardness of cubic polycrystalline boron nitride. This is a classic super-hard material that is widely used. The hardest material known to mankind so far is diamond. For a long time there have been attempts, which continue to this day, to discover a material harder than diamond. So far, these attempts have not led to success.

Why are superhard materials needed? The number of superhard materials is small, about ten, maybe fifteen materials known today. Firstly, superhard materials can be used for cutting, polishing, grinding, and drilling. For tasks related to machine tool building, jewelry making, stone processing, mining, drilling, and so on, all this requires super-hard materials.

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

Moreover, superhard materials may still be useful in body armor and other protective military devices. In particular, a material such as boron carbide, which is also super-hard and quite light, is widely used. This is the range of application of superhard materials.

It is known that superhard materials are formed in substances with strong covalent bonds. Ionic bonding reduces hardness. The metal bond also reduces hardness. The bonds must be strong, directed, that is, covalent, and as short as possible. The density of the substance should also be as high as possible, density in the sense 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 of High Pressure Physics in the Moscow region, the Institute of Superhard and New Carbon Materials in the Moscow region, the Institute of Superhard Materials in Kyiv and a number of laboratories in the West. Active developments in this area began, I think, in the 50s, when artificial diamonds were first produced 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, precisely 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. - these are molecules similar to a soccer ball, hollow molecules, round or somewhat elongated. The bonds between these molecules are very weak. That is, it is a molecular crystal consisting 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 hard structure. This material was named tisnumite in honor of the Technological Institute of Superhard and New Carbon Materials. It was assumed that this material was harder than diamond, but further research showed that this was most likely not the case.

There have been proposals and quite active discussion that carbon nitrides could be harder than diamond, but despite active discussion and active research, such a material has not yet been presented to the world.

There was a rather funny work by Chinese researchers, in which they suggested, based on theoretical calculations, that another modification of carbon is similar to diamond in many ways, but is slightly different from it, and is called lonsdaleite. According to this work, lonsdaleite is harder than diamond. Lonsdaleite is an interesting material; thin lamellae of this material have been found in shock-compressed diamond. This mineral was named after the famous woman Kathleen Lonsdale, a great British crystallographer who lived in the 50s–70s of the 20th century. She had an extremely interesting biography; she even spent time in prison when she refused to put out fires during World War II. She was a Quaker by religion, and Quakers were prohibited from any activities related to war, even putting 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 Crystallography, 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 drawn contrary to their own results.

Thus, it turns out that there is no real candidate to displace diamond as the hardest substance. But nevertheless, the issue is worth exploring. Still, many laboratories are still trying to create such a material. Using our method for predicting crystal structures, we decided to ask this question. And the problem can be formulated as follows: you are not looking for a substance that has maximum stability, but a substance that has maximum hardness. You give 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 evolutionarily try to find harder and harder 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 forms of carbon and so on - in all cases, 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 the sense of crack resistance or in terms of chemical resistance.

For example, elemental boron. We discovered the structure, a new modification of boron. We published this article in 2009, and it caused a tremendous response. The structure is obtained by applying slight 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 slightly reduce 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 pressures for synthesis are small, and therefore, in principle, one can even think about its synthesis in fairly large volumes.

We have predicted a number of other superhard phases, such as phases in the tungsten-boron system, chromium-boron, and so on. All of these phases are superhard, but their hardnesses are still at the lower end 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 that will be close to diamond in hardness. We and other colleagues have already done something in this area. But how to apply this technologically is not yet entirely clear.

I'll tell you about a new form of carbon, which was actually produced experimentally back in 1963 by American researchers. The experiment was conceptually quite simple: they took carbon in the form of graphite and compressed it at room temperature. The fact is that you can’t get a diamond this way; a diamond requires strong heating. Instead of diamond, a transparent superhard non-metallic phase was formed in their experiments, but nevertheless it was not diamond. And this was in no way consistent with the characteristics of any of the known forms of carbon. What's the matter, what kind of structure is this?

Quite by accident, while studying various carbon structures, we came across one structure that was only slightly inferior to diamond in stability. Only three years after we saw this structure, looked at it, even published it somewhere between the lines, it dawned on us that it would be nice to compare the properties of this structure with what has been published by all those researchers since 1963 and right up to very 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 discovered that a completely different structure of carbon also described the same experimental data. The problem is that the experimental data were of rather poor resolution. So who is right?

Soon, Swiss and Chinese researchers proposed a number of modifications. And towards the end, one 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 what is the right structure?

To do this, we had to study the kinetics of the transformation of graphite into various carbon structures, 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 was published in which the experimenters did the most accurate experiment with data of much better resolution than before, and it really turned out that out of all those dozens of published structures, only one structure explains the experimental data - it is still our structure. We called this new material M-carbon because 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 is superior to diamond is still unclear.

Until now it is, one might say, a “thing in itself.” We continue our search and hope that we will be able to invent a material that, while not much inferior to diamond in hardness, will significantly surpass 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 by 2 times. And this was done by Japanese researchers, and now you can see the products that they produce, quite 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 almost impossible to even polish them, and it takes a whole laboratory to polish it for weeks.

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

To instrumental superhard materials include diamonds and materials based on cubic boron nitride. Distinguish natural(A) and synthetic(AS) diamonds. Diamond is the hardest material. It has high wear resistance, good thermal conductivity, low coefficients of linear and volumetric expansion, low coefficient of friction and low adhesion to metals, with the exception of iron and steel. However, the strength of diamond is low. The hardness and strength of diamond varies in different directions. It is easier to process diamond in a direction parallel to the crystal faces, since in this direction the atoms are furthest apart from each other. The heat resistance of diamond is characterized by the fact that at a temperature of about 800 ° C under normal conditions it begins to transform into graphite. At the same time, diamond has the highest abrasive ability compared to other abrasive materials. The disadvantages of diamond include its ability to rapidly dissolve in iron and its alloys at temperatures of 750...800 °C. Diamond tools are characterized by high performance and durability. It is most effectively used when ob-

working of hard alloys, non-ferrous metals and their alloys, titanium and its alloys, as well as plastics. This ensures high dimensional accuracy and surface quality.

In order of increasing strength, decreasing fragility and specific surface area, synthetic diamond grinding powders are arranged as follows: AC2 (ASO), AC4 (ASR), AC6 (ASV), AC15 (ASK), AC32 (ACC). AC2 grains are well held in a binder and are recommended for making tools using an organic binder. AC4 grains are intended mainly for the manufacture of various tools on metal and ceramic bonds, AC6 - tools on metal bonds operating at high specific pressures, AC 12 - for processing stone and other hard materials, AC32 - for dressing abrasive wheels, processing corundum, ruby and other particularly hard materials.

Micropowders of the AM and AN brands are used from natural diamonds, and ACM and ASN from synthetic diamonds. AM and ACM micropowders of normal abrasive ability are intended for the manufacture of abrasive tools used to process hard alloys and other hard and brittle materials, as well as parts made of steel, cast iron, and non-ferrous metals when it is necessary to obtain a high surface cleanliness.

Micropowders AN and ASN, which have increased abrasive ability, are recommended for processing super-hard, brittle, difficult-to-process materials. The grain size of powders is indicated by a fraction, the numerator of which corresponds to the largest, and the denominator to the smallest grain size of the main fraction.

In order to increase the efficiency of diamond abrasive tools, diamond grains coated with a thin metal film are used. Metals with good adhesive and capillary properties in relation to diamond are used as coatings - copper, nickel, silver, titanium and their alloys. The coating increases the adhesion of grains to the binder, promotes heat removal from the cutting zone, and provides the ability to orient grains in a magnetic field during tool manufacturing.

Cubic boron nitride (elbor, cubonite) are used for processing workpieces made of steel and cast iron. It is especially effective

application for final and profile grinding of heat-treated workpieces made of high-alloy structural heat-resistant and corrosion-resistant steels of high hardness and sharpening of steel cutting tools. At the same time, the consumption of abrasive tools is reduced by 50-100 times compared to the consumption of electrocorundum.

Depending on the indicator of mechanical strength, elbor is divided into grades: LO - normal strength, LP - increased mechanical strength, L KV - high-strength. CBN of normal mechanical strength is used for the manufacture of tools with an organic bond and grinding paper, CBN of increased mechanical strength is used for the manufacture of tools with ceramic and metal bonds, for rough grinding, depth sharpening, and processing of workpieces made of difficult-to-cut structural steels. Elbor brand L KV is used for the production of metal-bonded tools intended for work in difficult conditions.

Cubonite is produced in two grades: KO - normal strength, KR - increased strength. In addition, two grades of micropowders are produced from cubonite: normal (KM) and increased (KN) abrasive ability. Cubonite tools have the same performance properties as CBN tools. It is used for the same purposes.

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

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

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

Due to the high fragility of solid compounds and the difficulty of processing them, the manufacture of parts from them is in most cases impractical or uneconomical. Their main area of ​​application is solid components of composite materials and coatings applied in various 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 crusts, 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 - SV and Dismit - are obtained.

SV grade diamonds are used for drill bits and bits, as well as for cutting non-metallic materials.

Dismite is used for the manufacture of mining drilling 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. It is inferior in hardness to diamond, but significantly superior to it in heat resistance.

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

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

Carbide alloys and cutting ceramics are produced using powder metallurgy methods. Powder metallurgy is a field of technology that covers a set of methods for producing metal powders from metal-like compounds, semi-finished products and products made from them, as well as from their mixtures with non-metallic powders without melting the main component. The starting materials for hard alloys and metal-ceramics - powders - are obtained by chemical or mechanical methods. The shaping of blanks (products) is carried out in a cold state or when heated. Cold forming occurs by axial pressing on mechanical and hydraulic presses or by liquid pressure on an elastic shell into which powders are placed (hydrostatic method). By hot pressing in dies under a hammer (dynamic pressing) or by the gas-static method in special containers due to the pressure (15-400 thousand Pa) of hot gases, products are produced from poorly sintered materials - refractory compounds, which are used for the manufacture of hard alloys and metal-ceramics. The composition of such sintered refractory compounds (pseudo-alloys) includes non-metallic components - graphite, alumina, carbides, which give them special properties.

Hard sintered alloys and cutting cermets (metals + non-metallic components) have become widespread in tool production. According to the content of the main components powders in the mixture, hard sintered alloys are divided into three groups: tungsten, titanium-tungsten and titanium-tantalum-tungsten, by area of ​​application– for alloys for processing materials by cutting, equipping mining tools, for surfacing quickly wearing parts of machines, instruments and fixtures.

Physical and mechanical properties of hard alloys: tensile strength in bending – 1176–2156 MPa (120–220 KGS/mm2), density – 9.5-15.3 g/cm3, hardness – 79–92 HRA.

Hard alloys for chip-free processing of metals, surfacing of quickly wearing parts of machines, instruments and fixtures: VK3, VK3-M, VK4, VK10-KS, VK20-KS, VK20K. In the designation of grades of hard alloys, the letter “K” means cobalt, “B” means tungsten carbide, “T” means titanium and tantalum carbides; the numbers correspond to the percentage of powder components included in the alloy. For example, the VK3 alloy contains 3% cobalt, the rest is tungsten carbide.

The shortage of tungsten has necessitated the development of tungsten-free hard alloys that are not inferior in basic properties to sintered alloys based on tungsten carbides.

Tungsten-free and chromium carbide hard cermet alloys used in mechanical engineering for the manufacture of dies, drawing matrices, for spraying various materials, including abrasive ones, friction parts operating at temperatures up to 900 °C, cutting tools for processing non-ferrous metals.

2. Superhard materials

For the manufacture of various cutting tools, three types of superhard materials (SHM) are currently used in various industries, including mechanical engineering: natural diamonds, polycrystalline synthetic diamonds and composites based on boron nitrite (CBN).

Natural and synthetic diamonds have such unique properties as the highest hardness (HV 10,000 kgf/mm 2), they have very low: linear expansion coefficient and friction coefficient; high: thermal conductivity, adhesive resistance and wear resistance. The disadvantages of diamonds are low bending strength, brittleness and solubility in iron at relatively low temperatures (+750 °C), which prevents their use for processing iron-carbon steels and alloys at high cutting speeds, as well as during intermittent cutting and vibration. Natural diamonds are used in the form of crystals fixed in the metal body of the cutter. Synthetic diamonds of the ASB (balas) and ASPC (carbonado) brands are similar in structure to natural diamonds. They have a polycrystalline structure and have higher strength characteristics.

Natural and synthetic diamonds They are widely used in the processing of copper, aluminum and magnesium alloys, noble metals (gold, silver), titanium and its alloys, non-metallic materials (plastics, textolite, fiberglass), as well as hard alloys and ceramics.

Synthetic diamonds Compared to natural ones, they have a number of advantages due to their higher strength and dynamic characteristics. They can be used not only for turning, but also for milling.

Composite is a super-hard material based on cubic boron nitride, used for the manufacture of blade cutting tools. In terms of hardness, the composite approaches diamond, significantly exceeds it in heat resistance, and is more inert to ferrous metals. This determines its main area of ​​application - the processing of hardened steels and cast irons. The industry produces the following main brands of STM: composite 01 (elbor - R), composite 02 (belbor), composite 05 and 05I and composite 09 (PTNB - NK).

Composites 01 and 02 have high hardness (HV 750 kgf/mm2), but low bending strength (40–50 kg/mm2). Their main area of ​​application is fine and fine non-impact turning of parts made of hardened steels with a hardness of HRC 55–70, cast irons of any hardness and hard alloys of grades VK 15, VK 20 and VK 25 (HP^ 88–90), with a feed of up to 0.15 mm /rev and cutting depth 0.05-0.5 mm. Composites 01 and 02 can also be used for milling hardened steels and cast irons, despite the presence of shock loads, which is explained by more favorable dynamics of milling. Composite 05 occupies an intermediate position in hardness between composite 01 and composite 10, and its strength is approximately the same as that of composite 01. Composites 09 and 10 have approximately the same bending strength (70-100 kgf/mm 2).

3. Materials of abrasive tools

Abrasive materials divided into natural and artificial. The former include quartz, emery, corundum and diamond, and the latter include electrocorundum, silicon carbide, boron carbide, cubic boron nitride and synthetic diamonds.

Quartz(P) is a material consisting mainly of crystalline silica (98.5...99.5% SiO2). It is used for the production of sanding pads on paper and fabric bases in the form of sanding grains in a free state.

Emery(H) – finely crystalline aluminum oxide (25...60% A l2 O 3) of dark gray and black colors with an admixture of iron oxide and silicates. Designed for the production of emery cloth and whetstones.

Corundum(E and ESB) is a mineral consisting mainly of crystalline aluminum oxide (80.95% Al2O3) and a small amount of other minerals, including those chemically associated with Al2O3. Corundum grains are hard and, when destroyed, form a conchoidal fracture with sharp edges. Natural corundum has limited use and is used mainly in the form of powders and pastes for finishing operations (polishing).

Diamond(A) is a mineral that is pure carbon. It has the highest hardness of all substances known in nature. Single-edged cutting tools and diamond metal pencils for dressing grinding wheels are made from crystals and their fragments.

There are four types of electrocorundum:

1) normal electrocorundum 1A, smelted from bauxite, its varieties - 12A, 13A, 14A, 15A, 16A;

2) white, smelted from alumina, its varieties - 22A, 23A, 24A, 25A;

3) alloyed electrocorundum, smelted from alumina with various additives: chromium 3A with varieties 32A, 33A, 34A and titanium 3A with variety 37A;

4) A4 monocorundum, smelted from bauxite with iron sulfide and a reducing agent, followed by the separation of corundum single crystals.

Electrocorundums consist of aluminum oxide Al 2 O 3 and a certain amount of impurities.

Silicon carbide– a chemical compound of silicon with carbon (SiC). It has greater hardness and brittleness. than electrocorundum. Depending on the percentage of silicon carbide, this material comes in green (6C) and black (5C) colors. The first contains at least 97% silicon. The second type (black) is produced in the following varieties: 52C, 53C, 54C and 55C. Various abrasive tools (for example, grinding wheels) for processing hard alloys and non-metallic materials are made from grains of green silicon carbide, and tools (grinding wheels) for processing products made of cast iron, non-ferrous metals and for sharpening cutting tools (cutters) are made from grains of black silicon carbide , drills, etc.).

Cubic boron nitride(CBN) is a compound of boron, silicon and carbon. CBN has a hardness and abrasive ability close to diamond.

Synthetic diamond (AS) has the same structure as natural diamond. The physical and mechanical properties of good grade synthetic diamonds are similar to those of natural diamonds. Synthetic diamonds are produced in five grades: ASO, ASR, ASC, ASV, ACC.