RU2732258C1 - Method of producing composite material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of composite material based on diamond particles. Method involves forming a workpiece from a mixture consisting of diamond particles, impregnating the workpiece with molten silicon at temperature of 1420–1500 °C. Diamond particles are represented by cut diamond particles of two fractions - small particles with particle size of 20–28 mcm and large particles with size of 200–250 mcm. Charge contains not less than 60 vol. % of diamond particles with size of more than 200 mcm, and ratio in charge of sizes of particles of small and large fractions is 1:6–1:10. After moulding, workpiece is heat treated in inert gas medium or in vacuum at 700–800 °C. Workpiece impregnation with silicon melt is carried out in vacuum or inert gas medium with formation of cubic silicon carbide and diffusion-reaction Turing process at diamond-cubic silicon carbide interface. Obtained material can be used in designs for various purposes, where it is necessary to combine or dominate one or more of the listed properties: high modulus of elasticity, low density, high hardness and other physical and mechanical properties. When impregnating workpieces from diamond particles of two fractions with liquid silicon, reaction growth of grains of crystalline silicon carbide is provided, which with diamond particles forms a structure corresponding to three times periodic surfaces of minimum energy.

EFFECT: there is provided a material having the following set of physicomechanical properties: density p = 3_2–3_40 g/cm³, elastic modulus E_El = 746–760 GPa and a Vickers hardness HV = 65–70 GPa.

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Description

The invention relates to a method for producing composite materials based on diamond particles and can be used in various industries, including machine tool building, mechanical engineering, engine building in the manufacture of structures for various purposes, friction units, nozzles of sandblasting machines, engine parts, etc.

The choice of diamond to create a composite with properties that allow it to be used under extreme loads is ensured by the fact that diamond exhibits the highest level of mechanical properties. However, according to economic indicators, it is impossible to obtain dimensional materials from diamond. Also, the technological disadvantage of diamond is its phase transition to graphite, which occurs at a temperature of about 800 ° C and complicates the sintering of pure diamond particles.

Diamond-containing polycrystalline materials, in which diamond particles are bound by a non-metallic refractory matrix, are obtained, as a rule, by sintering initial diamond particles ranging in size from 1 to 60 μm in the presence of small additions of metals, more often silicon.

Known patent (RU No. 2347744, publ. 02/27/2009), which presents a wear-resistant material containing diamond, as well as a binder phase, which can be cobalt and at least one of the following elements - Ti, Zr, Hf, V, Nb, Ta, Cr, Mo. Sintering is carried out under a high pressure of 5.7-7.5 GPa at a temperature of 1400-1900 ° C, which is energy-intensive and economically less profitable.

Known patents (RU # 2151126, publ. 20.06.2000, RU # 2206502, publ. 27.10.2002 and RU # 2270821, publ. 27.02.2006), where a matrix of diamond particles and silicon carbide impregnated with liquid silicon is used as a basis ... The materials have high wear resistance; however, the introduction of silicon carbide into the initial charge mixture sharply decreases the modulus of elasticity, hardness, and a number of other properties of the resulting composite.

The closest patent (prototype patent) to the claimed one is (RU # 2036779, publ. 09.06.1995), where ASM 3/2 diamond particles are used as a matrix. Despite the high properties of these materials, they have a number of disadvantages, in particular, the use of diamond particles of one fraction in composites leads to a low density of blanks, which undoubtedly reduces the level of mechanical properties of finished products. The use of small diamond particles leads to their partial combustion (up to 50% of the initial amount of diamond particles), which also negatively affects the level of mechanical properties of sintered materials.

The technical result of the present invention is to create a method for producing a composite material based on diamond particles, having a structure consisting of triple periodic surfaces of minimum energy, having a complex of physical and mechanical properties: density p = 3.32-3.40 g / cm ³ ; modulus of elasticity E _control = 746-760 GPa; Vickers hardness HV = 65-70 GPa.

The technical result is achieved due to the fact that during the implementation of the method for producing composite materials, such process conditions are selected that promote the synthesis of silicon carbide as a result of the diffusion-reaction Turing process and the formation of triple periodic surfaces of minimum energy.

The method of obtaining composite materials is implemented in several stages as follows.

1. Forming blanks

The first stage of the method is to obtain blanks containing diamond particles. Mixtures of diamond particles of two fractions with a size of 20-28 μm and 200-250 μm are used as the initial charge for forming blanks, which leads, on the one hand, to the achievement of greater compactness of molding and an increase in mechanical properties, and on the other hand, the presence of large and small diamonds, provides a combination of high abrasive properties with high wear resistance.

To achieve the maximum packing of particles during the molding of diamond powders, a two-fraction mixture of powders was used, subject to the use of a face-centered cubic (FCC) packing model, which makes it possible to achieve a space filling factor of 79.4%. For tight packing, the size ratio of small and large particles should be 1: 6 - 1:10. The selected fcc structure consists of 8 large powder particles, forming a cube, on the edges of which small particles are located between four large particles. For tight packing, large particles should be 6-10 times larger than small particles.

It is important that faceted diamond particles are used to obtain composite materials; this is a necessary condition for the implementation of the diffusion-reaction Turing process, which leads to the formation of a strong framework with a high diamond content ("skeleton"). The word "skeleton" is commonly used in silicon carbide technology.

When molding, it is advisable to use a temporary binder, which simplifies the molding process. An alcoholic solution of phenol-formaldehyde resin was used as a temporary binder, but other temporary binder additives can be used. The amount of binder (dry resin) introduced into the workpiece does not exceed 5% of the mass of diamond particles. The use of resin makes the preform stronger and easier to work with.

For pressing workpieces, molding methods are used in molds (semi-dry molding method), however, other methods can be used to obtain dense workpieces: hydrostatic and injection molding, slip casting, as well as methods of inkjet and laser printing.

When forming blanks, it is necessary to ensure a uniform distribution of diamond particles over the volume of the mold, therefore, before forming, the powders were granulated by rubbing through sieves.

After molding, the preforms are dried at temperatures of 120-150 ° C to remove moisture and excess binder. This stage is the final one when receiving blanks.

The described molding methods provide preforms with a relatively high porosity (from 35 to 45 vol.%), While most of the pores are open.

2. High temperature heat treatment of workpieces

Heat treatment is carried out in an inert gas atmosphere or in vacuum at temperatures of 700-800 ° C. At a higher heat treatment temperature, the probability of partial graphitization of diamonds increases. The process begins on the surface of diamond particles and gradually penetrates into depth, which leads to the formation and growth of a graphite layer on the surface of diamond particles. In some cases, the process of high-temperature heat treatment of workpieces can be omitted.

3. Impregnation of blanks with silicon melt

Silicon melt is used to impregnate the workpieces. Impregnation is carried out in a vacuum or inert gas by melting silicon directly on the surface of the workpieces, dipping them into the melt or pouring silicon melt onto the surface of the porous workpieces.

The impregnation is carried out at temperatures exceeding the melting point of silicon - 1420-1500 ° C. Molten silicon penetrates into the volume of the compacted composite (workpiece) and reacts with amorphous carbon and graphite, forming cubic silicon carbide (Fig. 1). The process is accompanied by an instant temperature rise and continues until the components are completely consumed. Within a short time, all amorphous carbon, graphite and silicon are consumed, and the reaction mass can be heated to a temperature of 2700 ° C. As a result, conditions for the diffusion-reaction Turing process are created at the diamond - cubic silicon carbide interface (Fig. 2).

As a result of impregnation of workpieces of diamond particles with liquid silicon, an almost porous material is obtained, consisting of diamond - 88-92 vol. and crystalline silicon carbide - 8-12 vol. %.

It should be noted that during the implementation of the described method there is no noticeable change in shape, i.e. the final products have almost the same dimensions and shape as the original blanks. If it is necessary to obtain products of a more complex shape, additional machining of the blanks can be carried out. It is more convenient to carry out such a processing of the workpieces after the stage of high-temperature heat treatment before silicon impregnation. Such workpieces are more durable and can be processed, for example, by turning, drilling, milling, etc.

In contrast to the prototype patent, the developed method makes it possible to obtain composite materials with the highest level of mechanical properties, which is the main indicator for wear-resistant, heat-resistant, armor and other materials.

Example 1. A charge mixture was prepared from ASM 28/20 (GOST 9206-80) and ASM 250/200 (GOST 9206-80) diamond particles in a ratio of 20/80 (composition 1, table 1). For this, a binder was added to the diamond particles - a 25% alcohol solution of phenol-formaldehyde resin brand SF-010-A (GOST 18094-80) in an amount of 4 wt. % dry resin by weight of diamond particles. The mixture was thoroughly mixed and ground through sieves.

Samples with dimensions of 50 × 50 × 8 mm were molded by pressing the charge in a metal mold at room temperature at a pressure of 100-150 MPa. The shaped blanks were kept in air at room temperature for 5-10 hours, followed by drying at a temperature of 150 ° C to a humidity of the blanks of 3-5%. The workpieces obtained in this way have a porosity of 35-45 vol. %.

The blanks were impregnated with a silicon melt at a temperature of 1420-1500 ° C for 10 min in a vacuum. As a result, products were obtained in the form of tiles with a size of 50 × 50 × 8 mm, in which diamond particles are bound by grains of crystalline silicon carbide, forming a structure of triple periodic surfaces of minimum energy (Fig. 3, Fig. 4).

Example 2. To obtain samples of composite materials used diamond particles grade ASM 28/20 (GOST 9206-80) and grade ASM 250/200 (GOST 9206-80) in a ratio of 20/80 (composition 2, table 1). The technology for obtaining samples is similar to example 1, however, before impregnation with liquid silicon, the samples were additionally heat treated in vacuum (pressure - 0.1 mm Hg) at 800 ° C for 10 minutes. The specified conditions of heat treatment make it possible to avoid graphitization of diamond particles.

Example 3. To obtain samples of composite materials used diamond particles grade ASM 28/20 (GOST 9206-80) and grade ASM 250/200 (GOST 9206-80) in a ratio of 10/90 (composition 3, table 1). The technology for obtaining samples is similar to example 1, but the amount of binder (phenol-formaldehyde resin) is 5 wt. % dry resin by weight of diamond particles.

The physical and mechanical properties of composite materials are shown in Table 2.

Thus, the implementation of the proposed method allows you to obtain composite materials, if necessary, in the form of parts of complex shapes and large sizes. In this case, the resulting materials have the highest level of mechanical properties due to an increase in the amount of initial diamond particles (up to 92 vol.%), The introduction of a large number of large diamond particles (larger than 200 microns) - not less than 60 vol. %, the use of charge mixtures, including diamond particles of two fractions of different sizes, and the implementation of the process in accordance with the Turing reaction, which leads to the formation of a material with a structure consisting of triple periodic surfaces of minimum energy.

The technical and economic effect of the claimed invention is to create a more economical technology in comparison with the technology described in the prototype patent.

Claims (4)

1. A method of obtaining a composite material based on diamond particles, including forming a workpiece from a charge consisting of diamond particles, impregnating the workpiece with a silicon melt at a temperature of 1420-1500 ° C, characterized in that cut diamond particles of two fractions are used as diamond particles - small with a particle size of 20-28 microns and a large one with a size of 200-250 microns, and the charge contains at least 60 vol.% of diamond particles larger than 200 microns, and the ratio in the charge of particle sizes of small and large fractions is 1: 6-1: 10 , while after forming, the workpiece is heat treated in an inert gas atmosphere or in vacuum at a temperature of 700-800 ° C, the workpiece is impregnated with a silicon melt in a vacuum or inert gas environment to ensure the formation of cubic silicon carbide and the Turing diffusion reaction process at the diamond interface - cubic silicon carbide. 2. The method according to claim 1, characterized in that forming the blanks includes preparing a charge by adding to the diamond particles a binder in the form of a 25% alcohol solution of phenol-formaldehyde resin in an amount of 4-5 wt.% Of dry resin from the mass of diamond particles, mixing and grinding through sieves. 3. The method according to claim 1, characterized in that the molding is carried out with the calculation of the particle packing, which ensures the achievement of the maximum density according to the face-centered cubic packing model with a space filling factor of up to 79.4%. 4. The method according to claim 1, characterized in that the impregnation is carried out to obtain a non-porous material consisting of diamond particles - 88-92 vol.% And crystalline silicon carbide - 8-12 vol.%.

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