RU2413699C2 - Superhard material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of superhard material which contains CVD diamond and which can be used in making a wheel dressing tool, a cutting, drilling tool etc. The surface of the CVD diamond is partially or completely covered by a shell under high pressure and temperature, where the said shell has a frame made from polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) with a bond between diamond-diamond grains or cBN-cBN grains, between which an activating additive is placed. The surface area of the shell surrounding the CVD diamond is not less than 40% of the surface of the CVD diamond; said shell contains 70-95 wt % PCD or PCBN and 5-30 wt % activating additive. If the shell is made from polycrystalline material based on PCD, the activating additive contains silicon and/or at least one transition metal, and if made from polycrystalline material based on PCBN, the activating additive contains aluminium and/or nitrides, borides and/or salicides of group IlIa, IVa, IVb, Vb, VIb, VIIb and VIII metals. The CVD diamond component of the superhard material can be polycrystalline as well as monocrystalline and can have different shapes and dimensions.

EFFECT: obtaining superhard material with high compression strength and thermal stability.

4 cl, 5 tbl, 2 dwg

Description

The invention relates to the production of a superhard material (STM) containing CVD diamond, which can be used in the manufacture of tools for dressing grinding wheels, cutting tools, drilling tools, etc., namely, the production of superhard polycrystalline materials based on diamond and cubic boron nitride ( cBN) under conditions of their thermodynamic stability.

CVD diamond, which is obtained by growing from a gas phase (Chemical Vapor Deposition, CVD) began to spread rapidly in the early 80s, when it became possible to obtain it on an industrial scale. Polycrystalline and single crystal films and CVD diamond wafers with diameters of more than 100 mm and thicknesses from micrometers to 1-3 mm are available today, obtained using the CVD process at temperatures of 700-1000 ° C and an operating pressure of 30-100 Top.

In contrast to diamond ceramics obtained by sintering diamond powder, CVD diamond synthesized from the gas phase does not contain a binder [Ralchenko VG, Ashkinazi E.E. Synthesis conditions, abrasive and laser processing of polycrystalline CVD diamond. // Instrumental light. - 2005. - No. 3. - S.14-18]. In its characteristics, it is more similar to single crystals of diamond. With a rather high purity of the reaction gases, the nitrogen content (the main impurity in natural and synthetic crystals) in diamond can easily be increased to 1 ppm.

The diamond material produced by the CVD process is characterized by a morphology that is sensitive to exact growth conditions. The growth rates for different deposition processes can vary significantly, and it usually turns out that higher growth rates can be achieved only due to the corresponding loss in quality of CVD diamond.

Table 1 shows the main physical properties of CVD diamonds according to the data of Diamond Materials Gmbh (http://www.diamond-materials.de).

Table 1 Knoop hardness, GPa up to 110 Young's modulus, GPa 900-1100 Poisson's ratio 0.1 Breaking strength, MPa up to 1200 Density, g / cm ³ 3,515 The coefficient of thermal expansion, K ^-1 1.0 × 10 ^-6 Thermal conductivity at room temperature, W · m ^-1 K ^-1 > 1800

The thermal stability of CVD diamond is 870–920 K (according to the data given in the brochures of Element Six).

Along with the main applications in electronics, CVD diamond is increasingly used as a tool material, in particular as an abrasive and as a coating on cutting tool inserts. A variety of cutting and drilling tools such as drill heads, reamers, countersinks with CVD diamond coatings, etc. is now commercially available for machining non-ferrous metals, plastics, and composite materials. Preliminary tests have shown that such CVD diamond coated tools have a longer life, provide faster cutting speeds and better finish than conventional tungsten carbide carbide inserts. These facts were confirmed by a survey of representatives of five leading German tool companies [http://www.stankoinform.ru/journal/werkzeuge. htm2]. It was emphasized that the application of CVD coatings with a thickness of 15-25 microns to tools for turning, drilling, and milling increase their efficiency in the processing of titanium, aluminum alloys, and composites. Moreover, they serve not as a replacement, but as an addition to polycrystalline diamonds. In addition, effective technological solutions for applying these coatings to hard alloys are known [JP 3094062, MKI ² C22C 1/05, C23C 16/26, C23C 16/27. Diamond-coated sintered hard alloy / Minoru N., Toshio N. - Publ. 04/18/1991]. It is reported that sales of diamond-coated tools in 2004 totaled EUR 20 million, and by 2010 it is expected to increase by 10 times.

The company SF Diamond Co, Ltd (China) offers a straightening tool made of CVD diamond in the form of columns obtained by laser cutting a workpiece grown by CVD method.

A fairly wide range of diamond tools obtained by CVD (CDD, CDM, CDE) is offered by Element Six. The company recommends producing diamond pencils, mandrel diamonds, diamond needles, a straightening tool, combs, and rollers from these diamonds.

However, attention must be paid to a number of technological obstacles to obtaining an effective CVD diamond tool. First of all, it is characteristic for diamond in general and CVD diamond in particular, an extremely low coefficient of thermal expansion, and secondly, it is the anisotropy of the properties of CVD diamonds. These factors in the manufacture of CVD diamond-based tools by traditional methods and its operation often lead to the occurrence of dangerous thermal stresses in the material, which lead to its destruction. Therefore, for a short time, the heating temperature in the manufacture of the tool should not exceed 870-920 K. According to the recommendations of the company Element Six [http://www.e6.com/en/resources/literatureproductsheets/monocrystal diamond /], special attention should also be paid to orienting the worker element (it is necessary to maintain the direction of 100, otherwise the tool life is reduced by 50-70%. In some cases (in particular, in the manufacture of combs), crystals are placed with an orientation of 111. In addition, the thickness of the CVD diamond used in the tool, does not exceed 0.6 mm. T Thus, the use of CVD diamond in the tool in the form of samples of finite dimensions (and not in the form of coatings) causes significant technological difficulties, in particular, due to the stresses that arise in CVD diamond, it cannot be used in a drilling tool, and in tools that work under heavy loads.

These difficulties should be significantly reduced in the manufacture of CTMs based on CVD diamond under the conditions of thermodynamic stability of diamond and cBN due, in particular, to the fact that stresses will be relieved in CVD diamond under high pressures and temperatures.

The closest in technical essence to the proposed material is a superhard material containing CVD diamond [Patent WO9323204, IPC ² С04В 35/583, С23С 16/26, Diamond Compact / Catalano JA, Lacy RB - publ. November 25, 1993], which is obtained in two stages. At the first stage, a compact material is obtained by sintering at high pressures and temperatures of cBN powders, diamond, and other superhard materials without additives that activate the sintering process. At the second stage, a CVD diamond layer is deposited on a compact material using the CVD process in a gaseous medium at a temperature of 700-1000 ° C and low pressures (30-100 Top), which, in particular, fills the pores and creates a single whole body of superhard material .

A significant disadvantage of this method is the inability to enter CVD diamond into closed pores in which graphite or amorphous carbon will form, which reduces the physicomechanical properties of the obtained superhard material.

Thus, the main problems that need to be solved in the manufacture of STMs based on CVD diamond are, firstly, the provision of a single whole between the CVD diamond and the surrounding frame of superhard material. The solution to this problem will significantly reduce the influence of the anisotropy of the physical properties of CVD diamond on the operational characteristics of the tool, increase its strength and thermal stability. The second important problem that needs to be solved is the elimination of the possibility of the formation of undesirable impurities of graphite or amorphous carbon in the pores in the case of using a shell of polycrystalline diamond (PCD) or hexagonal boron nitride, boron oxides in the case of using a shell of polycrystalline cubic boron nitride (PCBN) which significantly reduce the operational characteristics of the material.

The basis of the invention is the task of such an improvement in superhard material, in which due to the surrounding of its surface partially or completely under high pressure and temperature by a shell of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) with a bond between diamond-diamond grains or grains cBN-cBN, between which the activating additive is placed, such technical effects as the implementation of strain hardening, reduction of the influence of anisotropy of physical properties are provided CVD-diamond in the performance of his manufactured with use of the tool, thereby increasing the compressive strength and thermal stability of the STM, as well as the efficiency of ruling, cutting, drilling tools in general.

The problem is solved in that for a superhard material containing CVD diamond, according to the invention, the surface of CVD diamond is partially or completely at high pressure and temperature surrounded by a shell of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) with a bond between the grains diamond-diamond or cBN-cBN grains, between which an activating additive is placed, while the area of the shell covering the CVD diamond is at least 40% of its surface; said shell contains 70-95 wt.% PCD or PCBN and 5-30 wt.% activating additives;

when the shell is made of a polycrystalline material based on PCD, the activating additive contains silicon and / or at least one of the transition metals of the Periodic system of elements, and when the shell is made of a polycrystalline material based on PCBN, the activating additive contains aluminum and / or nitrides, borides and / or silicides of metals IIIa, IVa, IVb, Vb, VIb, VIIb and VIII groups of the Periodic system of elements.

The CVD diamond component of the superhard material can be either polycrystalline or monocrystalline, including doped with, for example, boron, it can have different shapes and sizes, including in the form of a powder.

For the formation of a polycrystalline shell, cBN, synthetic or natural diamond powders can be used, the sizes of which can vary from the nanometric range to 100 microns.

A causal relationship between the claimed combination of features and the technical results that are achieved during its implementation is as follows.

The formation of a superhard material based on CVD diamond must be carried out under the conditions of thermodynamic stability of diamond and cBN.

This is due to the fact that a characteristic feature of the polycrystalline shell of a material based on diamond or cBN is the presence of a continuous rigid framework of intergrown diamond or cBN grains, which is formed in the region of thermodynamic stability of diamond and cBN. The grains that make up the frame are, in fact, single crystals of diamond or cBN, which combine unique physical, mechanical and thermophysical properties. How much these properties are realized in a polycrystal depends on the degree of diamond-diamond bond or, respectively, cBN - cBN. The main role in this process belongs to the plastic deformation of the particles of the material forming the shell, namely diamond or cBN, for which a large proportion of covalent bonds is characteristic, and in the case of such materials, as is known, the presence of high pressures and temperatures is necessary for their effective consolidation by plastic deformation. that correspond to the thermodynamic stability of these materials [Polycrystalline materials based on diamond / Shulzhenko A.A., Gargin V.G., Shishkin V.A., Bochechka A.A. Repl. ed. Novikov N.V .; USSR Academy of Sciences. Institute of superhard materials. - K .: Science. Dumka, 1989. - 192 p.].

Thus, in CVD diamond-based material manufactured under conditions of thermodynamic stability of diamond or cBN, diamond-diamond or cBN - cBN bonds, respectively, are provided. As a result, the created polycrystalline shell and CVD diamond are a single whole, and since the components of the material are close in their physical properties, the effect of thermal stresses will be significantly lower during the manufacture and operation of the tool than in the case of using traditional materials based on CVD diamond, which will to contribute to the efficiency of its use by increasing strength and thermal stability and, as a consequence, the growth of wear resistance.

Optimum according to the invention is such a formation of a polycrystalline shell around a CVD diamond, in which the area of the shell that covers the CVD diamond is at least 40% of its surface.

This is due to the following. We experimentally established that the initial hardness of CVD diamond from the germinal side is 77 GPa. The hardness of sintered CVD diamond surrounded by polycrystalline PCD diamond was 124 GPa, and this at a sintering temperature of 1600 K.

Processing at the same pressure and temperature of CVD diamond without a polycrystalline shell does not increase its hardness.

It was also found that if CVD diamond is surrounded by a polycrystalline shell by an amount less than 40%, then the effect of increasing hardness is reduced.

In the manufacture of superhard material based on CVD diamond, the following important fact is also taken into account. The temperature of the onset of plastic deformation, in particular for diamond micropowders, is 1230 K at a pressure of 7 GPa. It was experimentally established that during sintering, the pressure at the contact points of diamond grains can reach 130 GPa. At the same time, in the pores between the diamond particles the pressure during sintering is much lower, which causes the formation of graphite or amorphous carbon in them [Polycrystalline materials based on diamond / Shulzhenko AA, Gargin VG, Shishkin VA, Bochechka A.A .; Repl. ed. Novikov N.V .; USSR Academy of Sciences. Institute of superhard materials. - K .: Science. Dumka, 1989. - 192 p.]. To overcome this undesirable effect, it is necessary to use additives that activate the sintering process.

Due to the introduction of an activating additive into the initial charge, the degree and rate of physicochemical processes during the formation of superhard material during sintering increases, while in the manufacture of STMs based on CVD diamond, the activating additive, firstly, prevents chemical interaction with oxygen due to chemical interaction leading to the formation of volatile oxides and, as a result, increases the porosity of the material. Secondly, interacting with other impurities (in particular, with graphite or amorphous carbon), the activating additive significantly reduces their negative effect on the physicomechanical properties of the framework, while the number of pores also decreases. In addition, the activating additive helps to reduce the temperature of the onset of plastic deformation at the grain contacts, which increases the strength of the polycrystalline frame. The activating additive also accelerates diffusion processes in the contact zone of diamond grains or cBN, resulting in the creation of strong bonds diamond-diamond or cBN-cBN.

The amount of activating additive, which is 5-30 wt.%, Represents the optimal boundaries at which the most effective interaction with impurities in the pores is ensured.

The STM was formed in a high-pressure apparatus (AED) of the toroid type. It is possible to use other types of AEDs, which ensure the creation of a high-pressure cell in the reaction volume during sintering, pressure above 4.0 GPa at a temperature above 1300 K. When the reaction volume of the high-pressure cell is equipped, various variants of the mutual arrangement of CVD diamond and the charge forming polycrystalline shell around it. Examples of some locations of CVD diamond 1 in a shell of PCD or PCBN 2 are shown in FIG.

Other options for the mutual arrangement of the CVD diamond and the mixture are possible.

It should be noted that when forming a polycrystalline shell, any substances that will reduce the porosity of the material can be used as an activating additive. But when forming a shell of a polycrystalline material based on PCD, it is optimal when the activating additive contains silicon and / or at least one of the transition metals of the Periodic system of elements.

In the case of using silicon as an activating additive, due to its interaction with graphite or amorphous carbon, silicon carbide is formed in the pores (see Fig. 2, which illustrates the formation of a polycrystalline diamond-based shell with silicon as an activating additive: CVD diamond 1; diamond 3; diamond-diamond bond 4; silicon carbide (SiC) 5.

The creation of an additional diamond - carbide bond leads to an increase in the total strength of the polycrystalline shell.

Table 2 shows the main physicochemical characteristics of a polycrystalline shell based on diamond with silicon as an activating additive.

table 2 Density, g / cm ³ 3.45 Knoop hardness, GPa 50-55 Crack resistance, MPa / m ^1/2 10-12 Compressive strength, GPa 2.2-3.1 Young's modulus, GPa 970 Thermal conductivity, W / (m · K) 250-300 Thermostability, K ~ 1500

When using active additives from a number of transition metals of the Periodic system of elements (for example, Fe, Ni, Co, 50% Co-50% Ni, etc.), their ability to dissolve carbon is taken into account, which will facilitate the conversion of graphite or amorphous carbon into diamond and, as consequence, the formation of additional diamond-diamond bonds.

Table 3 shows the main physicochemical characteristics of a polycrystalline shell based on diamond with cobalt as an activating additive.

Table 3 Density, g / cm ³ 3.74-3.77 Knoop hardness, GPa fifty Crack resistance, MPa / m ^1/2 10-13 Compressive strength, GPa 3.2 Young's modulus, GPa 1000 Thermal conductivity, W / (m · K) 500 Thermostability, K 1000-1200

When using activating additives consisting of silicon and transition metals of the Periodic system of elements (for example, TiSi, ZrSi ₂ , etc.), both of the above-mentioned mechanisms of formation of the structure of a polycrystalline shell are realized, namely, due to the interaction of graphite or amorphous carbon in pores with silicon, additional diamond - carbide bonds, and the result of interaction with transition metals are additional diamond-diamond bonds. The properties of the obtained diamond-based polycrystalline shell will correspond to Table 2 or Table 3, depending on the ratio of the components of the activating additive.

When the shell is made of a material based on PCBN, the activating additive contains aluminum and / or nitrides, borides, and / or silicides of metals IIIa, IVa, IVb, Vb, VIb, VIIb, and VIII of the Periodic Table of the Elements. The shell is formed at high pressures and temperatures that correspond to the thermodynamic stability of cBN by reactive sintering of cBN powders with aluminum and / or the aforementioned refractory compounds. Such conditions provide a polycrystalline shell structure, which is a continuous framework formed by directly contacting cBN grains and distributed along grain boundaries where there is no such contact connecting ceramics from refractory compounds. The composition of ceramics is determined by the reactions that take place between the components that form the shell, including impurities.

The optimal amount of activating additive, which is 5-30 wt.%, Provides the optimal combination of the contact surface cBN-cBN with the contact surface cBN - refractory ceramics. The strength of such contacts and the physicomechanical properties of ceramics formed due to activating additives determine the complex of physicomechanical properties of the shell based on PCBN (Table 4).

Table 4 The main physicochemical characteristics of the shell based on PCBN with an activating additive Density, g / cm ³ 3.35-3.38 Knoop hardness, GPa 28-30 Crack resistance, MPa / m ^1/2 10.5 Ultimate compressive strength, GPa 2.9 Young's modulus, GPa 920 Thermal conductivity, W / (m · K) 70 Thermostability, K 1400

Examples of specific implementations of the invention are given in table 5.

Table 5 No. p / p STM The composition of the activating additive The amount of activating additives, wt.% Compressive strength, GPa Thermostability, K one diamond Si 10 3,1 1500 2 diamond TiSi ₂ 5 2.9 1500 3 diamond ZrSi ₂ fifteen 2.2 1500 four diamond Co 10 3.2 1100 5 diamond Co-ni thirty 2,8 1000 6 diamond no - 1.4 720 7 cBN Al 8 2.9 1400 8 cBN Aln fifteen 2.7 1350 9 cBN Si ₃ N ₄ thirty 2.7 1380 10 cBN GeSi 8 2,4 1300 eleven cBN TiB ₂ twenty 2.6 1400 12 cBN TiN fifteen 2.6 1380 13 cBN CrB ₄ 6 2,3 1320 fourteen cBN Nisi ₂ 8 2.5 1340 fifteen cBN no - 1.4 720

Examples 1-5 and 7-14 are given for those cases that relate to the claimed features.

Examples 6 and 15 are provided for those cases that are beyond the scope of the claimed features. As you can see, in the absence of an activating additive during the formation of a polycrystalline shell, the strength and thermal stability of the superhard material are significantly reduced.

Thus, due to the fact that CVD diamond is in a shell made of polycrystalline diamond or cBN, and sintering is carried out at high pressures and temperatures, the thermal stability of the manufactured superhard material significantly increases (from 870 to 1500 K, depending on the type of activating additive). In addition, during sintering under conditions of high pressures and temperatures, strain hardening is realized in CVD diamond, which contributes to a significant increase in the physicomechanical properties of the superhard material and it becomes possible to use it in a drilling tool and other types of tools that operate at high loads.

Claims (4)

1. A superhard material containing CVD diamond, characterized in that its surface is partially or completely at high pressure and temperature surrounded by a shell of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) with a bond between the diamond - diamond grains or grains cBN-cBN, between which activating additive is placed. 2. The material according to claim 1, characterized in that the area of the shell covering the CVD diamond is at least 40% of its surface. 3. The material according to claim 1, characterized in that the said shell contains 70-95 wt.% PCD or PCBN and 5-30 wt.% Activating additives. 4. The material according to claim 1, characterized in that when the shell is made of a polycrystalline material based on PCD, the activating additive contains silicon and / or at least one of the transition metals of the Periodic system of elements, and when the shell is made of a polycrystalline material based on PCBN, the activating additive the additive contains aluminum and / or nitrides, borides and / or silicides of metals IIIa, IVa, IVb, Vb, VIb, VIIb and VIII of the Periodic Table of the Elements.

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