RU2740599C1 - Method of producing polycrystalline diamond material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used in making cutting tools. Method of producing polycrystalline diamond material includes placing high pressure chamber in reaction cell in zone of maximum temperature of heating of rod from metal-catalyst, having end working surface, and carbon-containing material, forming a shell around the core. Reaction cell is exposed to high pressure and temperature in the region of thermodynamic stability of diamond. End working surface of rod is equipped with barrier layer. Barrier layer is made from metal having a melting point higher than the melting temperature of the catalyst metal and which is not in the synthesis conditions by the diamond formation catalyst. Thickness of barrier layer makes 0.05–0.5 mm.

EFFECT: invention widens the field of use of polycrystalline diamond material by reducing the weakened transition zone in the obtained material while maintaining the overall geometric dimensions of the diamond polycrystalline material.

7 cl, 7 dwg, 1 ex

Description

The invention relates to a method for producing a polycrystalline diamond material, mainly a carbonado-type material.

Polycrystalline diamond materials (diamond polycrystals) consist of intergrown small diamond crystallites. These materials are isotropic, so they are in many cases preferable to single crystals of diamonds and can replace them in various tools, such as drilling tools, cutters, dies, smoothers and others. The synthesized polycrystalline diamond materials are obtained by the action of high pressures and temperatures in the region of the thermodynamic stability of diamond on the carbon-containing material and the metal-catalyst in contact with each other. Under these conditions, the carbon-containing material in the presence of a metal catalyst is transformed into diamond. However, as a result of the processes occurring in the high-pressure chamber, various inclusions of a non-diamond structure are found in the diamond polycrystal, such as residues of the metal catalyst, the products of the interaction of the metal catalyst with carbon, residual graphite, and the reaction products of the materials from which the chamber parts are made. The inclusions significantly reduce the strength, wear resistance, and heat resistance of polycrystalline diamond material, and, accordingly, reduce the service life of the tools.

It was found that the barriers enclosing the synthesis zone in the high-pressure chamber limit the ingress of non-diamond inclusions into the polycrystalline diamond material.

In GB1000702, cl. B01J3 / 062, 1965, a method for producing a polycrystalline diamond material is proposed, in which a metal catalyst substrate is surrounded with a carbonaceous material, the assembly is placed in a barrier tube and subjected to high pressure and temperature. The barrier tube is made of a material whose melting point is higher than the melting point of the catalyst metal. The barrier tube protects the diamond synthesis zone from the ingress of unwanted inclusions formed outside the synthesis zone, for example, reaction products of catlinite, talc, etc., which emit volatiles or melt and flow in the direction of the catalyst metal, and have a negative effect on the process of converting carbonaceous material into diamond.

However, during the synthesis of diamond crystals, a large number of inclusions of a non-diamond structure are formed inside the barrier tube, i.e. in the zone of the reaction cell, where the carbonaceous material and the metal catalyst are located. So in the process of formation of diamond crystals at elevated pressure and temperature, the metal catalyst melts and moves into the volume of the carbon-containing material. In this case, a transition zone enriched in metal inclusions and depleted in diamond crystals is formed in the diamond polycrystal at the interface between the carbon-containing material and the metal-catalyst. This area cannot be used for tool making. As a result, the size of the polycrystal decreases by the size of the transition zone, limiting the area of its application.

In the known method for producing polycrystalline diamond material described in the source SU1533218, class. C01 B31 / 06, 1987, the barrier layer is placed between the carbonaceous material and the metal catalyst, separating them from each other. The barrier layer is made of ammonium salt. The purpose of the barrier layer is to limit the ingress of the catalyst metal into the transition zone of the polycrystal.

The disadvantage of this method is that the porous barrier layer does not prevent the penetration of the metal catalyst into the carbon-containing material and, accordingly, the formation of a transition zone in the diamond polycrystal saturated with the metal catalyst. In addition, the products of the interaction of ammonium salts and the metal catalyst remain inside the synthesized diamond polycrystal, falling into the diamond polycrystal together with the metal solvent. In addition to the metal catalyst, such a transition zone contains large inclusions of a material chemically foreign to the diamond polycrystal with reduced strength and hardness.

The closest technical solution for obtaining a polycrystalline diamond material of the carbonado type of large sizes is a technical solution according to US4049783 class. С01В31 / 06, 1977. The known method includes exposure to high pressure and temperature in the region of diamond stability on a substrate of a carbon-containing material installed in the reaction cell of a chamber of high pressures and temperatures in the presence of a metal catalyst. The substrate is made in the form of a rod located at one end inside the workpiece made of carbon-containing material, and at the other end in contact with the cooling element of the high-pressure chamber. The peculiarity of the method lies in the fact that the working surface of the rod, on which the formation of polycrystalline diamond occurs, has a linear dimension of no more than 0.1-0.2 linear dimensions of the carbon-containing material, while the metal-catalyst is located in the reaction cell in the zone of the maximum heating temperature. When exposed to high pressure and temperature in the region of thermodynamic stability of diamond, thermobaric conditions are created on the working surface of the rod, ensuring the production of a diamond polycrystal with a fine-grained structure and a minimum content of localized non-diamond inclusions.

The disadvantage of this method is that the carbonaceous material and the metal catalyst in the reaction cell are in contact with each other. With an increase in pressure and temperature as a result of processes occurring in the near-contact zone, the catalyst metal melt, in the absence of special restrictive means, moves into the volume of the carbon-containing material and forms a weakened transition zone in the polycrystalline diamond material with an increased content of the catalyst metal. In this case, the metal catalyst forms large metal inclusions in this zone, amounting to tenths of a millimeter. Since the working surface of the resulting diamond polycrystal is initially limited in linear dimensions, the formation of a weakened zone in the polycrystal in the contact zone of the carbon-containing material and the catalyst metal, significantly reduces the working dimensions of the obtained polycrystalline diamond material and thereby narrows the area of its use.

The technical objective of the invention is to expand the areas of application of polycrystalline diamond material by reducing the weakened transition zone in the polycrystalline material without reducing the overall geometric dimensions of diamond polycrystals.

To solve a technical problem in a method for producing a polycrystalline diamond material, including placing a high-pressure and temperature chamber in the reaction cell in the zone of the maximum heating temperature of a rod made of a metal catalyst having an end working surface and a carbon-containing material that forms a shell around the rod, and affecting the reaction cell with high pressure and temperature in the region of thermodynamic stability of diamond, the end working surface of the rod is equipped with a barrier layer made of metal with a melting point higher than the melting point of the metal catalyst and is not a catalyst for the formation of diamond under the synthesis conditions, while the barrier layer has a thickness of 0, 05-0.5 mm.

The barrier layer can be made in the form of a foil.

The barrier layer can be made with variable thickness, increasing towards the zone with the maximum heating temperature.

The increasing barrier layer can be hemispherical or conical. The layer can be located on the working surface of the metal catalyst rod with a bulge directed into the rod or towards the carbon-containing material. Also, the increasing barrier layer can have a biconvex shape.

The essence of the invention is as follows.

The synthesis of polycrystalline diamond material proceeds at high pressures and temperatures, while after loading the reaction cell to the operating pressure, heating is performed by direct current flow through the carbon-containing material to the melting point of the metal catalyst. In the area of contact of the end working surface of the metal-catalyst and the carbon-containing material in the zone of maximum temperature, the growing melt of the metal-catalyst in the volume creates a high local pressure, leading to the appearance of cracks in the near-contact surface of the carbon-containing material. Cracks can be up to 2 mm. The barrier layer on the end working surface of the rod, made of metal impermeable to the melt, does not allow the melt to contact in this zone with the carbon-containing material and, accordingly, penetrate into its cracks and pores. The metal catalyst flows to the periphery of the rod, flows around the barrier layer and enters the zone of carbonaceous material. In this zone, in the presence of a metal catalyst, the transformation of the carbon-containing material into diamond begins, which leads to a decrease in the local pressure due to the volumetric effect of the graphite-diamond transformation. Due to the resulting pressure drop, a new portion of the metal catalyst is injected at the diamond formation boundary, which promotes the synthesis of the next portion of diamond. In the process of transformation of graphite into diamond, the heating current decreases due to the general increase in the electrical resistance of the reaction cell, as a result of which the temperature in the cell decreases. The process of converting the carbonaceous material to diamond occurs until either all of the reactive carbonaceous material is converted to diamond, or the temperature drops to values below the melting temperature of the catalyst metal.

The method is illustrated by figures.

FIG. 1 shows the equipment of the reaction cell, which contains a metal-catalyst made in the form of a rod, a barrier layer made in the form of a foil, and a carbon-containing material surrounding the rod.

FIG. 2 shows a working cell with a grown polycrystalline diamond material.

FIG. 3 shows a rod-shaped catalyst metal and a foil-shaped barrier layer.

FIG. 4 shows a metal catalyst made in the form of a rod and a barrier layer with a variable thickness increasing towards the zone of the maximum heating temperature, i.e. the barrier layer is made in the form of a hemisphere.

FIG. 5 shows a metal catalyst made in the form of a rod and a barrier layer with variable thickness increasing towards the zone of maximum heating temperature, i.e. the barrier layer is made in the form of a cone.

FIG. 6 shows a rod-shaped catalyst metal with a biconvex barrier layer.

FIG. 7 shows a carbonado-type polycrystalline diamond material.

The method is carried out as follows.

The reaction cell (Fig. 1) of the high-pressure chamber contains a graphite heater 1, inside which is installed an electrical insulating layer 2 of hexagonal boron nitride. To carry out the synthesis, a metal catalyst 3 is placed inside the electrically insulating layer, which is preferably made in the form of a rod. The rod has an end working surface 4 for the formation of a polycrystalline diamond material. On the end working surface 4 of the rod there is a barrier layer 5. The free space in the reaction cell is filled with carbon-containing material 6. The rod in the carbon-containing material is placed so that its end working surface 4 with a barrier layer 5 is surrounded by carbon-containing material 6 in the zone of maximum heating temperature 7. After equipping the high-pressure chamber, the pressure is increased and heated to the melting point of the metal catalyst. The reaction cell is heated by direct current flow through the carbon-containing material. After heating, the process of diamond formation begins, which ends within a few seconds, after which the heating is turned off, the pressure is reduced to atmospheric pressure, and the polycrystal 8 is removed (Fig. 7).

Polycrystal 8 consists of intergrown small diamond crystallites and in the area of contact of the carbon-containing material with the barrier layer has a small transition zone 9 containing a small amount of the metal catalyst.

Metals or its alloys having a melting point higher than the melting temperature of the catalyst metal are taken as the material of the barrier layer. The main requirement for the metal barrier layer is that it must be impermeable to the molten metal catalyst. The metallic material should not be a catalyst for the formation of diamond under the conditions of synthesis, should not undergo compression and deformation, while maintaining integrity under the conditions of synthesis, not react with the components involved in the synthesis, and should not release any substances that contaminate the polycrystalline material. As such a material, metals can be used: molybdenum, niobium, tantalum, tungsten, titanium, or alloys of these metals that satisfy the above conditions.

The barrier layer can be made in the form of foil 5 with a thickness of 0.05-0.5 mm. If the thickness of the barrier layer is less than 0.05 mm, the layer will dissolve in the melt of the metal catalyst, and the process of diamond synthesis may be disrupted and the weakened zone of the polycrystal may increase. An increase in the thickness of the barrier layer more than 0.5 mm will lead to a decrease in the height of the forming polycrystal, which will limit the scope of its application.

In other embodiments, the barrier layer may be of varying thickness, increasing towards the zone of the maximum heating temperature of the reaction cell. The barrier layer can be made in the form of a hemisphere 10, in the form of a cone P. of a biconvex shape 12. The barrier layer, made in the form of a hemisphere or a cone, can be located on the metal-catalyst rod with a bulge towards the carbon-containing material (in Fig. 2 and Fig. 3, the layer is shown by a solid line), or directed into the depth of the metal catalyst rod (in Fig. 2 and Fig. 3, the layer is shown by a dashed line). Since at high pressures the transformation of graphite into diamond proceeds with the release of heat - the heat of crystallization, the increased thickness of the barrier layer in the zone of the maximum heating temperature ensures the removal of a certain amount of heat from the zone of maximum heating, contributing to the acceleration of the process and an increase in the resulting diamond crystals in the polycrystal.

As the carbon-containing material, materials such as amorphous carbon, charcoal, anthracite and other carbon materials subjected to high-temperature heat treatment can be used, but it is preferable to use pure graphite with a high crystalline perfection.

The concept of a metal catalyst includes both at least one metal and metal alloys, metal compounds with inclusions of carbides, borides, intermetallic compounds, which can facilitate the catalytic conversion of a carbon-containing material into diamond and have a liquid-phase state under synthesis conditions. Electrolytic nickel can be used as a metal catalyst; nickel-chromium alloys; iron with chromium; nickel, iron and chromium; hard alloy powders and others.

Depending on the metal-catalyst, diamond polycrystals are synthesized at a pressure of 6-12 GPa at the melting temperature of the metal-catalyst. Usually the synthesis time is 3-30 sec.

Examples of

A graphite heater with an inner diameter of 5 mm was placed in a toroid-type reaction chamber with an inner diameter of 7 mm and a height of 9 mm. A rod made of a metal catalyst based on electrolytic nickel was placed inside the heater. A tantalum foil 0.1 mm thick was placed on the end working surface of the rod. The free space of the reaction cell was filled with a carbon-containing material - graphite of the MGOSCH grade. The reaction cell was loaded with a pressure of 8.0 GPa, and the temperature was raised to 2000K. The synthesis conditions were maintained for 15 sec. The obtained polycrystalline material - carbonado - was a cylinder 4.3 mm high and 4.2 mm in diameter. The transition zone was 0.3 mm, the working zone minus the catalyst zone and the transition zone was 3.0 mm. This material size is sufficient for the manufacture of nozzle, drawing tools, for which the size of the polycrystalline diamond material is essential. The cutting tool made of the obtained diamond polycrystal can withstand up to 8 regrinds.

Under similar conditions, a polycrystalline diamond material was obtained without using a barrier layer on the end face. The obtained polycrystalline material - carbonado - was a cylinder 4.3 mm high and 4.2 mm in diameter. The transition zone was 1.2 mm, the working zone minus the catalyst zone and the transition zone was 1.9 mm. This material size is not sufficient for the manufacture of nozzle and drawing tools. The cutting tool made from the obtained diamond polycrystal can withstand up to 3 regrinds.

Thus, the method makes it possible to expand the field of application of the polycrystalline diamond material by reducing the weakened transition zone in the material while maintaining the overall geometric dimensions of the diamond polycrystal.

Claims (7)

1. A method of obtaining polycrystalline diamond material, including placing a high-pressure chamber in a reaction cell in the zone of maximum heating temperature of a rod made of a metal catalyst having an end working surface and a carbon-containing material forming a shell around the rod, and exposing the reaction cell to high pressure and temperature in the field of thermodynamic stability of diamond, characterized in that the end working surface of the rod is equipped with a barrier layer made of metal with a melting temperature higher than the melting point of the metal catalyst and which is not a catalyst for the formation of diamond under the synthesis conditions, and having a thickness of 0.05-0.5 mm. 2. The method according to claim 1, characterized in that the barrier layer is made in the form of a foil. 3. The method according to claim 1, characterized in that the barrier layer is made with a variable thickness increasing towards the zone of the maximum heating temperature of the reaction cell. 4. A method according to claim 1, characterized in that the barrier layer is made in the form of a hemisphere, a cone. 5. The method according to claim 1, characterized in that the barrier layer is located on the working surface of the rod with a bulge directed towards the carbonaceous material. 6. The method according to claim 1, characterized in that the barrier layer is located on the working surface of the rod with a bulge directed into the depth of the rod. 7. The method according to claim 1, characterized in that the barrier layer is made of a biconvex shape.

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