home Translator Super-hard materials of the brand. Hard and superhard alloys

Super-hard materials of the brand. Hard and superhard alloys

Superhard materials (STM) - these include diamonds (natural and synthetic) and composite materials based on cubic boron nitride.

Diamond- one of the modifications of carbon. Due to the cubic structure of the crystal lattice, diamond is the hardest mineral known in nature. Its hardness is 5 times higher than that of a hard alloy, but the strength is low and natural diamond single crystals break into small fragments when critical loads are reached. Therefore, natural diamonds are used only in finishing operations, which are characterized by low power loads.

The heat resistance of diamonds is 700...800 °C (at more high temperatures the diamond burns). Natural diamonds have high thermal conductivity and the lowest coefficient of friction.

Natural diamond is designated by the letter A , synthetic - AC . Natural diamonds are individual single crystals and their fragments, or intergrown crystals and aggregates. Synthetic diamonds are obtained in the form of fine-grained powders and are used to make abrasive wheels, pastes and micropowders. A separate group consists of polycrystalline diamonds (PDA) of the ASB (Ballas) and ASPK (Carbonado) brands. PCD, due to its polycrystalline structure, resists impact loads much better than diamond single crystals, and, despite its lower hardness compared to natural diamond, has higher tensile and transverse shear strengths. The impact strength of diamond polycrystals depends on the size of the diamond grains and decreases with their increase.

Diamond has a chemical affinity for nickel- and iron-containing materials, so when cutting iron-based steels, contact surfaces diamond tool, intensive adhesion of the material being processed occurs. The carbon that makes up diamond reacts actively with these materials when heated. This leads to intensive wear of the diamond tool and limits the scope of its application, therefore natural diamonds are used mainly for fine turning of non-ferrous metals and alloys that do not contain carbon and iron. 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 from various polymer composite materials. The tool can be used for turning discontinuous surfaces and for milling, but its durability will be shorter than when machining without impact.

Processed material	V, m/min	s, mm/rev	t, mm
Aluminum cast alloys	600…690	0,01…0,04	0,01…0,20
Aluminum-magnesium alloys	390…500	0,01…0,05	0,01…0,20
Aluminum heat-resistant alloys	250…400	0,02…0,04	0,05…0,10
Duralumin	500…690	0,02…0,04	0,03…0,15
Tin bronze	250…400	0,04…0,07	0,08…0,20
Lead bronze	600…690	0,025...0,05	0,02…0,05
Brass		0,02…0,06	0,03…0,06
Titanium alloys	90…200	0,02…0,05	0,03…0,06
Plastics	90…200	0,02…0,05	0,05…0,15
Fiberglass	600…690	0,02…0,05	0,03…0,05

In many cases, the greater wear resistance of cutters made from synthetic diamonds, observed in practice, compared to cutters made from natural diamonds, is explained by the difference in their structures. In natural diamond, cracks appear on the cutting edge, develop and can reach significant sizes. In PCD (synthetic diamond), the resulting cracks are stopped by the boundaries of the crystals, which determines their higher, 1.5...2.5 times, wear resistance.

Another promising area of application for PCD is the processing of materials that are difficult to cut and cause rapid tool wear, such as particle boards, medium-density boards with a high adhesive content, coated with melamine resin, decorative laminate paper, as well as other materials. having an abrasive effect. Tools with PCD have a durability when processing such materials that is 200..300 times higher than the durability of carbide tools.

PCD tools in the form of replaceable polyhedral inserts have been successfully used in the processing of polymer materials. composite materials. Their use makes it possible to increase durability by 15...20 times compared to tools made of hard alloy.

Cubic boron nitride(KNB, BN ) is not found in nature; it is obtained artificially from “white graphite” at high pressure x and temperatures in the presence of catalysts. In this case, the hexagonal lattice of graphite turns into a cubic lattice, similar to the lattice of diamond. Each boron atom is connected to four nitrogen atoms. In terms of hardness, CBN is somewhat inferior to diamond, but has higher heat resistance, reaching 1300...1500 °C, and it is practically inert to carbon and iron. Like diamond, CBN has increased brittleness and low bending strength.

There are several brands of CBN, grouped under the “composites” group. Varieties of CBN differ from each other in size, structure and properties of grains, percentage composition of the binder, as well as sintering technology.

The most widely used composites are: composite 01 (elbor-R), composite 05, composite 10 (hexanite-R) and composite 10D (two-layer plates with a working layer of hexanite R). Of these, the strongest is composite 10 ( σ and = 1000...1500 MPa), therefore it is used for shock loads. Other composites are used for impactless finishing of hardened steels, high-strength cast irons and some difficult-to-cut alloys. In many cases, turning with composites is more effective than the grinding process, since, due to its high thermal conductivity, CBN does not cause burns when working at high cutting speeds and at the same time provides low surface roughness.

Composites are used in the form of small plates of square, triangular and round shapes, fixed to the tool body by soldering or mechanically. Recently, hard alloy plates with a layer of composite or polycrystalline diamond deposited on them have also been used. Such multilayer plates have greater strength, wear resistance and are more convenient for fastening. They allow you to remove allowances of great depth.

The main reserve for increasing processing productivity for tools based on BN is the cutting speed (Table 11.), which can exceed the cutting speed of a carbide tool by 5 or more times.

Table 11. Cutting speeds allowed by various tool materials

From the table it is clear that greatest efficiency application of tools based on BN occurs when processing high-hard cast irons, steels and alloys.

One of the possibilities for increasing the efficiency of a tool based on BN is the use of cutting fluids (coolants), which for tools made of BN it is most effective to use them by spraying them at cutting speeds up to 90...100 m/min.

Another effective area for using tools equipped with polycrystalline composites is the processing of surfacing, which is used to strengthen parts of metallurgical production. Welded materials of very high hardness (up to HRC 60..62) are produced by electric arc or plasma surfacing with flux-cored wires or tapes.

The areas of application for cutting speed and feed of all groups of considered tool materials are approximately shown in Fig. 38.

Fig.38. Scope of application of various tool materials according to cutting speed V and submission s .

1 – high-speed steels; 2 – hard alloys; 3 – hard alloys with coatings; 4 – nitride ceramics; 5 – oxide-carbide (black) ceramics; 6 - oxide ceramics; 7 – cubic boron nitride.

Synthetic superhard materials (SHM) used for blade tools are dense modifications of carbon and boron nitride.

Diamond and dense modifications of boron nitride, which have a tetrahedral distribution of atoms in the lattice, are the hardest structures.

Synthetic diamond and cubic boron nitride are obtained by catalytic synthesis and catalyst-free synthesis of dense modifications of boron nitride under static compression.

The use of diamond and boron nitride for the manufacture of blade tools became possible after they were obtained in the form of large polycrystalline formations.

Currently, there is a wide variety of STM based on dense modifications of boron nitride. They differ in their production technology, structure and basic physical and mechanical properties.

The technology for their production is based on three physical and chemical processes:

1) phase transition of graphite-like boron nitride to cubic:

BN Gp ® BN Cub

2) phase transition of wurtzite boron nitride to cubic:

BNVtc ® BN Cub

3) sintering of BN Cub particles.

Unique physical and Chemical properties(high chemical stability, hardness, wear resistance) of these materials are explained by the purely covalent nature of the bonding of atoms in boron nitride, combined with the high localization of valence electrons in the atoms.

The heat resistance of a tool material is its important characteristic. The wide range of values of thermal stability of BN (600–1450°C) given in the literature is explained both by the complexity of the physicochemical processes occurring when heating BN, and to some extent by the uncertainty of the term “thermal stability” in relation to STM.

When considering the thermal stability of polycrystalline STMs based on diamond and dense modifications of boron nitride (they are often composite and the amount of binder in them can reach 40%), it should be taken into account that their thermal stability can be determined both by the thermal stability of BN and diamond, and by changes in the properties of the binder during heating and impurities.

In turn, the thermal stability of diamond and BN in air is determined by both the thermal stability of high-pressure phases and their chemical resistance under given conditions, mainly with respect to oxidative processes. Consequently, thermal stability is associated with the simultaneous occurrence of two processes: oxidation of diamond and dense modifications of boron nitride by atmospheric oxygen and a reverse phase transition (graphitization), since they are in a thermodynamically nonequilibrium state.

According to the technology for producing diamond-based STMs, they can be divided into two groups:

1) diamond polycrystals obtained as a result of the phase transition of graphite into diamond;

2) diamond polycrystals obtained by sintering diamond grains.

The most common grain size is approximately 2.2 microns, and there are practically no grains whose size exceeds 6 microns.

The strength of ceramics depends on the average grain size and, for example, for oxide ceramics it decreases from 3.80–4.20 GPa to 2.55–3.00 GPa with increasing grain sizes, respectively, from 2–3 to 5.8–6.5 µm.

Oxide-carbide ceramics have an even finer grain size distribution, and the average grain size of Al 2 O 3 is generally less than 2 μm, and the grain size of titanium carbide is 1–3 μm.

A significant disadvantage of ceramics is its fragility - sensitivity to mechanical and thermal shock loads. The fragility of ceramics is assessed by the crack resistance coefficient - K WITH.

Crack resistance coefficient K C, or the critical stress intensity factor at the crack tip, is a characteristic of the fracture resistance of materials.

High hardness, strength and elastic modulus, complexity of mechanical processing and small sizes of STM samples limit the application of most currently used methods for determining the crack resistance coefficient.

To determine the crack resistance coefficient – K With STM, they use the method of diametrically compressing a disk with a crack and the method of determining the fracture toughness of ceramics by introducing an indenter.

To eliminate the brittleness of ceramics, various compositions of oxide-carbide ceramics have been developed.

The inclusion of monoclinic zirconium dioxide ZrO 2 in aluminum oxide-based ceramics improves the structure and thereby significantly increases its strength.

Tools equipped with polycrystalline diamonds (PCD) are designed for finishing non-ferrous metals and alloys, non-metallic materials instead of carbide tools.

Composite 01 and composite 02 - polycrystals from cubic boron nitride (CBN) with a minimum amount of impurities - are used for fine and finishing turning, mainly without impact, and face milling of hardened steels and cast irons of any hardness, hard alloys (Co > 15%) with depth cutting 0.05–0.50 mm (maximum permissible cutting depth 1.0 mm).

Composite 05 - polycrystalline sintered from CBN grains with a binder - is used for preliminary and final turning without impact of hardened steels (HRC< 60) и чугунов любой твердости с глубиной резания 0,05–3,00 мм, а также для торцового фрезерования заготовок из чугуна любой твердости, в т. ч. по корке, с глубиной резания 0,05–6,00 мм.

Composite 10 and two-layer plates from composite 10D (composite 10 on a hard alloy substrate) - polycrystals based on wurtzite-like boron nitride (WNB) - are used for preliminary and final turning with and without impact and face milling of steels and cast irons of any hardness, hard alloys (Co > 15%) with a cutting depth of 0.05–3.00 mm, intermittent turning (the presence of holes, grooves, and foreign inclusions on the machined surface).

Thus, STM tools based on boron nitride and diamond have their own areas of application and practically do not compete with each other.

The wear of cutters made of composites 01, 02 and 10 is a complex process with a predominance of adhesive phenomena during continuous turning.

With an increase in contact temperatures in the cutting zone above 1000°C, the role of thermal and chemical factors increases - the following intensify:

– diffusion;

– chemical decomposition of boron nitride;

– α phase transition;

– abrasive-mechanical wear.

Therefore, when turning steels at speeds of 160–190 m/min, wear increases sharply, and at v > 220 m/min it becomes catastrophic, almost regardless of the hardness of the steel.

During intermittent turning (with impact), abrasive-mechanical wear predominates with chipping and tearing out of individual particles (grains) of the tool material; the role of mechanical shock increases with increasing hardness of the matrix of the processed material and the volume content of carbides, nitrides, etc.

The greatest influence on the wear and durability of cutters during continuous turning of steels is the cutting speed, when turning with impact - speed and feed, when turning cast iron - feed, and the machinability of malleable cast iron is lower than that of gray and high-strength cast iron.

Work order

1. Study the grades and chemical composition of steels and alloys, the classification of steels by manufacturing method and purpose depending on the content of chromium, nickel and copper, requirements for macrostructure and microstructure, standardization of hardenability. Pay attention to the procedure for selecting samples to check hardness, microstructure, depth of the decarburized layer, surface quality, and fracture.

2. Investigate the microstructure of U10 steel samples. Evaluate the microstructure of heat-treated steel by examining it under an MI-1 microscope. Capture the microstructure in the computer and print it out.

When writing a report, you must provide a brief description theoretical foundations structure, properties of materials for cutting tools made of carbon tool steels, high-speed steels, hard, super-hard alloys and ceramic materials. Provide photographs of the microstructure of U10 steel obtained during examination under the MI-1 microscope; indicate the heat treatment mode and structural components in the caption. The results of measurements of the main parameters of several inclusions of the steel under consideration are included in the table. 3.19.

Table 3.19

Control questions

1. Classification of materials for cutting tools.

2. Structure and properties of tool carbon steels.

3. Structure and properties of die steels.

4. Structure and properties of high-speed steels.

5. Structure and properties of hard and superhard tool alloys.

6. Structure and properties of ceramic tool materials.

7. Structure of tool carbon steels.

8. Basic properties that a material for cutting tools should have.

9. Wear resistance and heat resistance of cutting tools.

10. What determines the heating temperature of the cutting edge of tools?

11. Chemical composition and modes heat treatment the most commonly used tool steels.

12. Hardenability of carbon steels, hardenability score, hardness distribution.

13. The influence of carbon content on the properties of carbon tool steels.

14. How is the tempering temperature of tools determined?

15. Hot hardness and red resistance of high-speed steel.

16. Reversible and irreversible hardness of high-speed steels.

17. How is the red resistance of high-speed steels structurally created?

18. How is red fastness characterized, its designation.

19. Heat treatment modes for high-speed steel tools, cold treatment, multiple tempering.

20. Steels for hot stamps, their heat resistance, heat resistance, toughness.

21. Operating temperatures for cutting tools made of hard alloys.

22. The hardness of metal-ceramic hard alloys, how is it determined?

23. Steels used for blade tools.

24. What explains the unique physical and chemical properties (high chemical resistance, hardness, wear resistance) of synthetic superhard materials?

25. A significant disadvantage of ceramics.

26. How is the fragility of ceramics assessed?

Laboratory work № 4

Dependency Research

composition – structure – properties For cast irons

Goal of the work: study of the structure, composition and properties of pig iron and machine-building cast iron; their classification and application.

Materials and equipment: collection of unetched sections of cast iron; metallographic complex, including an MI-1 optical microscope, digital camera Nikon Colorpix-4300 with photo adapter; etchant (4% solution of HNO 3 in alcohol).

Theoretical part

Cast iron are called iron-carbon alloys containing more than 2.14% carbon and permanent impurities - silicon, manganese, sulfur and phosphorus.

Cast irons have lower mechanical properties than steel, since the increased carbon content in them leads either to the formation of a hard and brittle eutectic, or to the appearance of free carbon in the form of graphite inclusions of various configurations, violating the continuity of the metal structure. Therefore, cast irons are used for the manufacture of parts that do not experience significant tensile and impact loads. Cast iron is widely used in mechanical engineering as a casting material. However, the presence of graphite also gives cast iron a number of advantages over steel:

– they are easier to process by cutting (brittle chips are formed);

– have better anti-friction properties (graphite provides additional lubrication of friction surfaces);

– have higher wear resistance (low coefficient of friction);

– cast irons are not sensitive to external stress concentrators (grooves, holes, surface defects).

Cast irons have high fluidity, fill molds well, and have low shrinkage, which is why they are used for making castings. Parts made from cast iron castings are much cheaper than those made by cutting from hot-rolled steel profiles or from forgings and stampings.

The chemical composition and, in particular, the carbon content do not sufficiently reliably characterize the properties of cast iron: the structure of cast iron and its basic properties depend not only on the chemical composition, but also on the smelting process, the cooling conditions of the casting and the heat treatment regime.

Carbon in the structure of cast iron can be observed in the form of graphite and cementite.

Depending on the state of the carbon, cast irons are divided into two groups:

1) cast irons in which all carbon is in a bound state in the form of cementite or other carbides;

2) cast irons in which all or part of the carbon is in a free state in the form of graphite.

The first group includes white cast iron, and the second group includes gray, malleable and high-strength cast iron.

According to their purpose, cast iron is divided into:

1) for conversion;

2) mechanical engineering.

Conversion ones are mainly used for the production of steel and malleable cast iron, and machine-building ones are used for the production of castings of parts in various industries: automobile and tractor manufacturing, machine tool building, agricultural engineering, etc.

White cast iron

In white cast iron, all carbon is in a chemically bound state (in the form of cementite), i.e. they crystallize, just like carbon steels, according to the metastable diagram Fe – Fe 3 C. They got their name from the specific matte white color of the fracture, due to the presence of cementite in the structure.

White cast iron is very brittle and hard, difficult to bend machining cutting tool. Pure white cast irons are rarely used in mechanical engineering; they are usually processed into steel or used to produce malleable cast iron.

The structure of white cast iron at normal temperature depends on the carbon content and corresponds to the “iron-cementite” equilibrium state diagram. This structure is formed as a result of accelerated cooling during casting.

Depending on the carbon content, white cast irons are divided into:

1) hypoeutectic, containing from 2 to 4.3% carbon; consist of perlite, secondary cementite and ledeburite;

2) eutectic, containing 4.3% carbon, consist of ledeburite;

3) eutectic, containing from 4.3 to 6.67% carbon, consist of perlite, primary cementite and ledeburite.

a B C

Rice. 4.1. Microstructure of white cast iron, × 200:

A– hypoeutectic (ledeburite, pearlite + secondary cementite);

b– eutectic (ledeburite);

V– hypereutectic (ledeburite + primary cementite)

Perlite in white cast iron is observed under a microscope in the form of dark grains, and ledeburite is observed in the form of separate sections of colonies. Each such area is a mixture of small rounded or elongated dark pearlite grains, evenly distributed in a white cementite base (Fig. 4.1, A). Secondary cementite is observed in the form of light grains.

With increasing carbon concentration in hypoeutectic cast iron, the proportion of ledeburite in the structure increases due to a decrease in the areas of the structure occupied by pearlite and secondary cementite.

Eutectic cast iron consists of one structural component - ledeburite, which is a uniform mechanical mixture of pearlite and cementite (Fig. 4.1, b).

The structure of hypereutectic cast iron consists of primary cementite and ledeburite (Fig. 4.1, V). With increasing carbon, the amount of primary cementite in the structure increases.

Related information.

One of the directions for improving the cutting properties of tools, which makes it possible to increase labor productivity during machining, is to increase the hardness and heat resistance of tool materials. The most promising in this regard are diamond and synthetic superhard materials based on boron nitride.

Diamonds and diamond tools widely used in processing parts made of various materials. Diamonds are characterized by exceptionally high hardness and wear resistance. In terms of absolute hardness, diamond is 4-5 times harder than hard alloys and tens and hundreds of times higher than the wear resistance of other tool materials when processing non-ferrous alloys and plastics. In addition, due to their high thermal conductivity, diamonds better remove heat from the cutting zone, which helps ensure the production of parts with a burn-free surface. However, diamonds are very fragile, which greatly limits their scope of application.

The main application for the manufacture of cutting tools is artificial diamonds, which in their properties are close to natural. At high pressures and temperatures in artificial diamonds it is possible to obtain the same arrangement of carbon atoms as in natural ones. The weight of one artificial diamond is usually 1/8-1/10 carats (1 carat - 0.2 g). Due to the small size of artificial crystals, they are unsuitable for the manufacture of tools such as drills, cutters and others, and therefore are used in the manufacture of powders for diamond grinding wheels and lapping pastes.

Blade Diamond Tools are produced on the basis of polycrystalline materials such as “carbonado” or “ballas”. These tools have long dimensional tool life and provide high quality treated surface. They are used in the processing of titanium, high-silicon aluminum alloys, fiberglass and plastics, hard alloys and other materials.

Diamond as a tool material has a significant drawback - when elevated temperature it enters into a chemical reaction with iron and becomes ineffective.

In order to process steel, cast iron and other iron-based materials, superhard materials, chemically inert to it. Such materials are obtained using a technology close to the technology for producing diamonds, but boron nitride, rather than graphite, is used as the starting material.

Polycrystals of dense modifications of boron nitride are superior in heat resistance to all materials used for blade tools: diamond by 1.9 times, high-speed steel by 2.3 times, hard alloy by 1.7 times, mineral ceramics by 1.2 times.

These materials are isotropic (the same strength in different directions), have a microhardness lower but close to the hardness of diamond, increased heat resistance, high thermal conductivity and chemical inertness with respect to carbon and iron.

The characteristics of some of the materials under consideration, which are currently called “composite,” are given in the table.

Comparative characteristics of STM based on boron nitride

Brand	Original title	Hardness HV, GPa	Heat resistance, o C
Composite 01	Elbor-R	60...80	1100...1300
Composite 02	Belbor	60...90	900...1000
Composite 03	Ismit	60	1000
Composite 05	Composite	70	1000
Composite 09	PCNB	60...90	1500
Composite 10	Hexanit-R	50...60	750...850

The effectiveness of using blade tools made from various grades of composites is associated with improving the design of tools and their manufacturing technology and determining the rational area of their use:

composites 01 (elbor-R) and 02 (belbor)

composite 05

composite 10 (hexanite-R)

At the same time, the service life of tools increases tens of times compared to other tool materials.

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

Table 2.18

Basic properties of synthetic superhard materials

Name of private label	Name	Hardness, HV, GPa	Heat resistance, °C
Ballas (ASB)	Synthetic diamond
Carbonado (ASPC)	Synthetic diamond
	Synthetic diamond
Composite 01
Composite 02 (05)
Composite 03
Composite 09
Composite 10	Hexaiit-R
Composite KP1 (KPZ)

Natural and 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 is one of the natural superhard natural materials. The name “diamond” comes from the Arabic al-mas, which translates as “the hardest,” or the Greek adamas, which means “insurmountable, indestructible, invincible.” At the end of the 18th century. It was found that diamond is made of carbon. Diamonds are found in the form of individual well-defined crystals or in the form of a cluster of crystal grains and numerous intergrown crystals (aggregates). The unit of measurement for the size of a diamond is the carat (from Arab, kirat), which is 0.2 g.

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

When sharpening, the diamond is first removed from the rod and ground in a technological holder on special machines using cast iron discs coated 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, tightly bound crystals with high strength and wear resistance.

Areas of application of private labels:

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) under high pressure and temperature, while the hexagonal face-centered lattice of graphite is transformed into a cubic face-centered diamond lattice. 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, through an appropriate chemical reaction it is possible to obtain a compound of these elements, i.e. boron nitride, which has a graphite-like hexagonal crystal lattice with approximately the same number of boron and nitrogen atoms arranged alternately. Similar to graphite, hexagonal boron nitride (HBN) has a layered, loose structure and can be transformed into CBN. This process is described by the state diagram of GNB - CBN. By adding special solvent catalysts (usually metal nitrides), the intensity of the transformation increases, and the pressure and temperature of the process are reduced, respectively, to 6 GPa and 1500°C. During the transformation, CBN crystals increase. When heated, individual CBN crystals are sintered together in contact zones and form a “polycrystalline" mass. To intensify sintering, solvents are also added. In addition, the entire sintered mass must be at a certain pressure and temperature to prevent the reverse transformation of hard CBN crystals into soft hexagonal crystals.

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

As a cutting material, diamond has high durability and a low coefficient of friction when paired with metal, which ensures high surface quality. Diamonds are used (natural and synthetic) for precision turning and boring of parts made of non-ferrous alloys. Diamonds are not used for processing carbon-containing metals (cast iron, steel), since due to the chemical affinity of the processed and tool materials, intensive wear of diamond cutters and carburization of the surface layer of the workpiece occurs.

Materials based on boron nitride are a crystalline cubic (CBN) or wurtzite-like (WNL) modification of a boron-nitrogen compound, synthesized using a technology similar to the production of synthetic diamonds. Due to variation technological factors Several different materials are obtained on this basis - elboron, cubonite, hexanite, etc. Polycrystals based on boron nitride are obtained with a size of up to 12 mm, 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 appearance of each is qualitative new group The development of tool materials is characterized primarily by a significant, abrupt increase in cutting speeds and is therefore always accompanied by profound changes in machine tool construction and machining technology.

Cutting speed - most important factor intensification of the processing of materials by cutting using tools made of synthetic superhard materials in conditions where the reserves for significantly increasing the 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 high speed cutting work is almost completely converted into heat and segmented chips are formed, the segments of which are separated by a fragile narrow bridge of heavily deformed metal; short, crushed chips are actually produced. Automation of material processing processes with chip removal and a further increase in cutting speeds are inseparable.

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

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

Polycrystals SV, SVS, dismite, SVBN, and carbonite are currently produced from materials obtained by sintering diamond grains.

Polycrystals of the ASB brand have a spherical shape with a diameter of about 6-6.5 mm, a clearly defined radial structure. Ballas crystals form a block structure and have different sizes across the cross-section of the sample: smaller in the center than at the periphery. Their size is in the range of 10-300 microns.

Diamonds of the ASPC brand have the shape of a cylinder with a diameter of 2-4.5 mm, a height of 3-5 mm, their structure is also radial, 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%.

In order of increasing strength, diamond polycrystals are arranged as follows: ASB, ASPK, SV, dismite.

Diamond tools can be operated, unlike composite tools, at low speeds inherent in carbide tools, providing a manifold increase in durability. When milling, speeds can be increased by 1.5-2 times. The cutting depth of wood-based particle board materials is determined by the width of the cutters or saws.

The effectiveness of using CA in processing high-hard 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 consistently ensuring the specified quality.

Processed material	Cutting speed, V, m/min	Innings, S, mm/rev	Depth of cut, t, mm
Aluminum and aluminum alloys
Aluminum alloys (10-20% silicon)
Copper and copper alloys (bronze, brass, babbitt, etc.)
Various composites (plastics, plastics, fiberglass, carbon fiber, hard rubber)
Semi-sintered ceramics and hard alloys
Sintered carbide
Wood-based materials
Rocks (sandstone, granite)

High wear resistance is revealed by tools made of ASP 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.

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

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

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 binder, titanium carbide alloys on a nickel-molybdenum binder. Widely used superhard materials: electrocorundum, zirconium oxide, silicon carbide, boron carbide, borazone, rhenium diboride, diamond. Superhard materials are often used as abrasive materials.

IN last years close attention of modern industry is directed to the search for new types of superhard materials and the assimilation of materials such as carbon nitride, boron-carbon-silicon alloy, silicon nitride, titanium carbide-scandium carbide alloy, alloys of borides and carbides of the titanium subgroup with carbides and borides of lanthanides.

Wikimedia Foundation. 2010.

See what “Superhard materials” are in other dictionaries:

Super hard ceramic materials- – composite ceramic materials obtained by introducing various alloying additives and fillers into the original boron nitride. The structure of such materials is formed by tightly bound tiny crystallites and, therefore, they are... ...

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 binder... ... Wikipedia

Fiberboard superhard boards SM-500- - are made by pressing ground wood pulp, treated with polymers, most often phenol-formaldehyde, with the addition of drying oils and some other components. They are produced in lengths of 1.2 m, widths of 1.0 m and thicknesses of 5–6 mm. The floors are made of... ... Encyclopedia of terms, definitions and explanations of building materials

powder materials- consolidated materials obtained from powders; In the literature, the term “sintered materials” is often used along with “powder materials”, because One of the main methods of consolidating powders is sintering. Powder... ... Encyclopedic Dictionary of Metallurgy

- (French abrasif grinding, from Latin abradere scrape) these are materials with high hardness and are used for surface treatment of various materials. Abrasive materials are used in the processes of grinding, polishing,... ... Wikipedia

Wikipedia has articles about other people with this surname, see Novikov. Wikipedia has articles about other people named Novikov, Nikolai. Novikov Nikolay Vasilievich ... Wikipedia

Grinding is a mechanical or manual operation for processing hard material (metal, glass, granite, diamond, etc.). A type of abrasive processing, which, in turn, is a type of cutting. Mechanical grinding is usually... ... Wikipedia

- (from the Middle Ages, lat. detonatio explosion, lat. detonо thunder), propagation of a zone of rapid exothermic at supersonic speed. chem. radio following the front of the shock wave. The shock wave initiates the radio, compressing and heating the detonating water... ... Chemical encyclopedia

Inorganic chemistry is a branch of chemistry associated with the study of the structure, reactivity and properties of all chemical elements and their inorganic compounds. This area covers all chemical compounds, with the exception of organic... ... Wikipedia

- ... Wikipedia

Books

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