DK154824B - POLYCRYSTALLIC DIAMOND BODIES AND PROCEDURES FOR PREPARING IT - Google Patents

Description

DK 154824 B

The invention relates to a polycrystalline diamond body / especially in the form of a disc, rod or hollow cylinder, with a mass of diamond crystals.

From US 2,391,589 there is known a polycrystalline diamond body, wherein the binder is a mixture of silicon carbide, boron carbide and alumina, and from US 4,042,347 a polycrystalline diamond body is known in which the binder is a metal and polymer matrix, but a technical barrier to obtaining of a high density diamond composite material (high volume diamond volume) and manufactured below the diamond stability pressure range has heretofore been a failure to develop a suitable binder capable of penetrating or infiltrating the capillary cavities in a densely packed fine particle size diamond powder. The binder must also form a thermally stable, strong bond with the diamond and must not transform the diamond into graphite 15 or react too far with the diamond.

According to the invention, the polycrystalline diamond body is characterized in that the diamond crystals are bonded to each other with a silicon atom-containing binder constituted by silicon carbide and free silicon, that the diamond crystals have a size of from 1 to 1000 µm, that the diamond crystal density in the body ranges from 65 to a maximum of 80% by volume of the body, that the proportion of silicon-containing binder constitutes up to 35% by volume of the body, that the binder is distributed substantially evenly within the body, that the proportion of the binder which contacts diamond surfaces is substantially composed of silicon carbide and that the diamond body is essentially pore-free.

The polycrystalline body of the invention is useful as abrasive material, cutting tool, nozzle or other abrasion resistant component.

The invention also relates to a process for producing the polycrystalline diamond body of the invention using a heat pressing step which is characterized by the characterizing part of claim 5.

In the method of the invention, pressures which are substantially lower than those required in the diamond stability range are used.

The invention will be further explained in the following with reference to the drawing, in which: Figure 1 shows a cross-section of an apparatus for producing 2

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a cavity in a pressure transmitting powder medium; Figure 2 shows a cross-section of an apparatus for exerting a substantially isostatic pressure on the cell, i.e. the cavity and contents, by means of a pressure transmitting powder medium for dimensional stabilization of the cell to produce a substantially isostatic system; Figure 3 shows a cross-section of a graphite form for simultaneously delivering heat and pressure to the substantially iso-static system and where the cell is seen contained therein, and Figure 4 shows a photograph (enlarged 690X) of a polished cross-section of a diamond body produced by the method of the invention wherein the diamond content was 72% by volume of the body. The 15 light gray-white phase in Figure 4 is the binder and the gray phase is diamond crystal. The dark spots are impurities.

In practicing the method of the invention, a mass of diamond crystals in contact with a silicon mass is subjected to a cold pressing step at ambient or room temperature to substantially complete stabilization of their dimensions substantially uniformly and then a hot pressing step, whereby the silicon seeps through the mass. of compressed diamond crystals.

25 The diamond crystal mass and the silicon mass can have many different shapes. Eg. each mass may take the form of one layer with one layer superimposed on the other. Alternatively, the silicon may be in the form of a tube or cylinder with a through cavity, and the diamond crystals may be packed in the silicon cylinder cavity. In another embodiment, the silicon may be in the form of a rod which may be centrally located in a cavity and the enclosing space between the silicon rod and the inner wall of the cavity may be packed with diamond crystals.

The diamond crystals used in the present method may be natural or synthetic, i.e. manmade. They vary in size with respect to largest dimension from approx. 1 pm to approx. 1000 µm, and the specific size or sizes used depend to a large extent on the particular packing or density of diamond crystals desired,

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3 and also of the particular use of the body provided. However, crystals of size less than 5 microns should be offered crystals larger than 10 microns, and crystals of less than 5 microns in size should preferably not constitute more than 50% by volume of the diamond blend to allow satisfactory silicon sieving. For most abrasive applications, diamonds crystals not greater than about 10 cm are preferred. 60 pm. Preferably, in order to maximize the diamond crystal packing, the crystals must be sorted by size to contain a variety of sizes, i.e. crystals of small, medium and large size. Preferably, the size-sorted crystals should be between ca. 1 pm and approx. 60 µm, and within this size range, preferably about 60% by volume to approx. 80% by volume of the total mass of crystals from the larger portion of the region, approx. 5-10% by volume is of medium size and the rest is made up of relatively small crystals or particles.

The classification of the diamond crystals is facilitated by the treatment of the larger diamond crystals in a jet mill. The diamond crystals are preferably chemically purified to remove any oxides or other impurities from their surfaces prior to use in the present process. This can be done by heating the diamond crystals in hydrogen at approx. 900 ° C for approx. 1 hour.

According to the present invention, silicon is used to infuse or seep into the pores or gaps between the diamond crystals. The silicon, e.g. may be in the form of a solid body or powder, used in an amount sufficient to fill the pores or gaps in the diamond crystal mass having a crystal density greater than 65% by volume of the volume occupied by the crystals. In general, the silicon can be used in an amount of between about 25% by volume and approx. 80% by volume, but to obtain the best results preferably from approx. 30 to approx. 60% by volume of the volume of diamond crystals with a crystal density greater than 65% by volume.

The present hot pressing step is carried out in an atmosphere which has no significant detrimental effect on the properties of the diamond crystals or the silicon ingested. In particular, the hot pressing step may be carried out in practically a vacuum or in an inert gas such as e.g. argon or helium, or it can be carried out in nitrogen or

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4 hydrogen. The present hot pressing is carried out sufficiently quickly so that no significant reaction occurs between the liquid silicon and nitrogen or hydrogen. The present hot pressing step cannot be carried out in atmospheric air since 5 diamonds in atmospheric air at more than 800 ° C are rapidly converted to graphite and the liquid silicon would be oxidized to form solid silicic anhydride before a significant infusion of liquid silicon into the diamond mass would have occurred.

Said hot pressing is carried out at between the temperature at which silicon becomes liquid and approx. At a pressure which need only be sufficient at the hot pressing temperature to break down interfacial refractory layers in the diamond mass which prevent liquid silicon penetration through the pores therein and usually this requires a minimum pressure of approx. 34.5 bar overpressure (500 psi). Specifically, the hot pressing pressure may vary from approx. 34.5 bar overpressure (500 psi) to approx. 1380 bar overpressure (20,000 psi), but it usually ranges between approx. 69 bar overpressure (1,000 psi) and approx. 690 bar overpressure (10,000 psi). Hot pressing pressure greater than approx.

20,690 bar overpressure (10,000 psi) provides no significant benefits. Likewise, temperatures higher than 1600 ° C provide no significant benefits and may lead to the conversion of the diamonds to graphite to a greater extent.

Here, a temperature at which silicon becomes liquid is understood to mean a temperature at which the silicon is able to flow easily.

When silicon is at its melting temperature, which in the literature is stated to go from ca. 1412 ° C to approx. 1430 ° C, it has a high viscosity, but as its temperature is raised it becomes less viscous and at a temperature of approx. 10 ° above its melting point it becomes liquid. The temperature at which the silicon is liquid is the temperature at which it will infuse or seep through the capillary-sized passages, gaps, or pores of the present compacted diamond crystal mass, having a crystal density greater than 65% by volume. With even further increase of 35, the flowability of the liquid silicon increases, resulting in a faster penetration rate through the diamond-crystal mass, and at the maximum heat-pressing temperature of approx.

At 1600 ° C, the liquid silicon has its greatest flowability and the fastest penetration rate through the crystal mass.

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With the apparatus shown in Figure 1, a cavity of predetermined size is extruded in a pressure transmitting powder medium 19a by means of a mold 9. At this point only sufficient pressure, usually approx. 690 bar overpressure (10,000 psi) to approx. 3450 bar overpressure (50,000 psi), with the plunger 23a for making the powder 19a at least substantially stable, so that when the pressure is removed, i.e. when the plunger 23a is withdrawn, the mold 9 can be removed leaving the cavity 11 which the mold has pressed into the powder.

The mold 9 may consist of any smooth surface 10 material, e.g. stainless steel or hard metal which can withstand the pressure released and which can be removed from the compressed powder and leave the cavity 11 as the mold has pressed therein.

When the mold 9 in Figure 1 is withdrawn leaving the cavity 11, a disc 12 of silicon and a diamond crystal mass are placed in contact with the silicon. To ensure that the diamond crystal mass has a thickness as desired for the resulting polycrystalline body, the cavity must be of such a size that there is no free space left therein, which would allow for the displacement or greater movement of the diamond particles 20 during later cold pressing which serves to stabilize the system in terms of dimensions, as shown in Figure 2. An additional amount of pressure transmitting powder is then placed over the cavity and its contents so as to provide a powder-enclosed cell 10, i. holiness and content, as shown in Figure 2.

As shown in Figure 2, cell 10 is then subjected to a cold pressing step performed at room or ambient temperature to which only sufficient pressure is required to provide a dimensionally stabilized, practically isostatic system. In Figure 2, the cell 10 in the cylindrical core of the printing mold 20 is surrounded 30 by a mass 19 which consists of pressure transmitting powder medium.

The present pressure transmitting powder medium contains very small particles, preferably sieve 0.037 mm (-400 mesh) particles, of a pressure transmitting powder medium which is kept practically unsintered under the pressure and temperature conditions used in the present process and which is practically inert to liquid silicon. Typical examples of such a powder are hexagonal boron nitride and silicon nitride. This pressure transmitting particle mass or this pressure transmitting powder medium causes the application of approximately or practically isostatic pressure of 6

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cell 10, whereby cell 10 and its contents are stabilized with respect to dimensions, i.e. densified, substantially uniform, providing a shaped, substantially isostatic system consisting of the powder-enclosed cell, in which the density 5 of the resulting compressed layer of crystals is greater than 65% by volume of the volume of the compressed crystals. The pressure mold 20 (ring 22 and pistons 23, 23a) can be made of tool steel, and if desired, the ring 22 may as shown be provided with a bushing. 22a of sintered cemented carbide to enable the application of 10 pressures as high as 13,800 bar overpressure (200,000 psi) at the cold pressing step shown in Figure 2. Pressures higher than 13,800 bar overpressure (200,000 psi) provide no significant benefit. Within the framework of the plunger 23, the bushing 22a and the plunger 23a, as shown in Figure 2 for the cold pressing step, pressure is preferably exerted in the range of from approx. 1380 bar overpressure (20,000 psi) to approx. 6900 bar overpressure (100,000 psi) and generally up to 3450 bar overpressure (50,000 psi) on the pressure transmitting powder medium by means of the pistons operated on conventional medium until the applied pressure is stabilized, as is done with conventional powder packing technology .

It should be noted that the particular cold pressing pressure to be used can be determined empirically, and pressures higher than the pressure which provides a dimensionally stabilized, practically isostatic system do not provide any significant additional densification or stabilization with respect to to dimensions of cell 10 and its contents.

The present pressure transmitting powder medium, e.g. hexagonal boron nitride and silicon nitride are of such a nature that, due to the uniaxially applied pressure, it provides an approximately hydrostatic effect, thereby exerting a practically isostatic pressure on the entire cell 10. It is assumed that the applied pressure practically unabated transmits to cell 10. The cold pressing step reduces the size of the pores, thereby maximizing the presence of capillary-sized pores in the crystal mass, which is convenient by providing the required diamond crystal density of over 65% by volume of the diamond mass.

This reduction in pore volume also decreases the final content of non-diamond material in the diamond mass and provides several, side-by-side, effective bonding to each other appropriately placed.

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7 lead crystal-to-crystal areas.

Upon completion of this cold pressing step, the density of the compressed diamond crystals in cell 10 should be over 65% by volume of the volume of crystals. Often, the diamond density of the 5 compressed diamond crystals can be between approx. 66% by volume and no more than approx. 85% by volume of the compressed diamond crystals. The higher the density of crystals, the less the amount of non-diamond material present between the crystals will be, resulting in a relatively harder abrasive body.

The practically isostatic system 21, which consists of the powder-enclosed cell provided by the cold-pressing step, is then subjected to a hot-pressing step, under which it is subjected to hot-pressing temperature and pressure simultaneously.

It is noted that when the cold pressing step is completed, one of the pistons 23, 23a is retracted, and, to a hard mass of practically isostatic shaped system 21, is forced out of a casing 22a and into a hole of identical diameter in a graphite form 30 so that the transferred system 21 is now enclosed by the walls of a hole 31 between the graphite pistons 32, 32a. The graphite mold 30 is provided with thermocouple 33 so as to provide an indication of the temperature applied to the dimensionally stabilized, practically isostatic system 21. The mold 30, with the thus substantially substantially isostatic system 21, is placed in a conventional hot pressing furnace not shown. The furnace chamber 25 is evacuated or evacuated almost completely, at least causing the evacuation of the system 21 including the cell 10, thereby providing in the system 21 and the cell 10 an almost complete vacuum in which the hot pressing step can be performed. However, at this point, nitrogen or hydrogen 30 or an inert gas species, such as argon, may be introduced into the furnace chamber to provide a suitable hot-pressing atmosphere in the chamber as well as in system 21 including the interior of cell 10. While pistons 32, 32a apply to the system 21 a uniaxial pressure, i.e. at the hot pressing pressure, its temperature is raised to a temperature at which the silicon wafer 12 is liquid.

During the hot pressing step, the hot pressing temperature must be reached quickly and usually maintained for at least 1 minute at such temperature below the hot pressing pressure to ensure satisfactory penetration through the diamond crystal mass. Generally, a

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8 pressing time pi from approx. 1 minute to approx. 5 minutes appropriate. Since the conversion of diamond into an elemental non-diamond carbon phase depends largely on time and temperature, ie. the higher the temperature and the longer the time at a side temperature, the more likely the conversion to elemental, non-diamond carbon, in the hot pressing step, is to be completed before 5% by volume of the diamond is converted to non-diamond pure carbon, and this can be determined empirically. Conversion of 5% by volume or more diamond to elemental, non-diamond carbon tends to result in a pure non-diamond carbon phase remaining in the final product, which will have a significant detrimental effect on its mechanical properties.

During the hot pressing step, the resilient interface layer or interface slag, which is mainly composed of oxide or carbide usually present or formed between the liquid silicon and diamond surfaces, due to the transfer of the hot pressing pressure into the liquid silicon, is expelled, after which infusion by hiring action takes place. Tests have shown that 20 infusion of the silicon into the diamond mass will not occur unless a pressure sufficient to break the slag is maintained and maintained in the system 21 during hot pressing while the silicon is liquid.

Further, in the present process, when the silicon becomes liquid, any slag or oxide formed or present therein will flow therein and be left as the liquid silicon penetrates the compacted diamond mass. As a result, the present diamond compact is devoid of any vitreous phase which would prevent a strong bond to form between the diamond and the silicon atom-containing binder.

As the liquid silicon, during hot pressing, seeps and flows through the diamond mass, it encapsulates the surfaces of the compressed diamond crystals and reacts with the diamond surfaces or with any phase of elemental, non-diamond carbon, optionally formed, thereby providing silicon carbide at the diamond crystals' surfaces. results in an integrated, highly bonded diamond body.

It is during this hot pressing step that it is particularly important to maintain practically isostatic conditions so that when

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The silicon is converted to the liquid stage, this liquid will not be able to pass between the mass 13 and the cavity 11 and escape to a significant extent but will be forced to move through the mass 13 of diamond crystals. The part of the pressure transmitting powder which is closely related to the contents of the cavity, ie. the portion of the pressure transmitting powder extending from the inner wall of the cavity or cell to preferably ca. 25 mm away, to prevent excessive leakage of liquid silicon during hot pressing, it should not contain interconnected 10 pores larger than approx. 5 pm.

After the hot pressing step is completed, at least a sufficient pressure must be maintained during the cooling of the hot pressed system 21, so that the hot pressed cell 10, which is kept in the system 21 during cooling, is subjected to a substantially isostatic pressure which is sufficiently high to maintain its stability in terms of dimensions. Preferably, the hot pressed system is allowed to cool to room temperature and the resulting present diamond body is removed. Optionally, excess silicon extruded on the outer surfaces of the polycrystalline diamond body can be removed by conventional methods such as e.g. by grinding.

The present polycrystalline diamond body comprises a mass of diamond crystals which are firmly bonded to each other by means of a silicon atom-containing binder consisting essentially of silicon carbide and pure silicon, and in which the diamond crystals have sizes of from about. 1 pm to approx. 1000 pm, where the density of diamond crystals varies from approx. 65% by volume to a maximum of approx. 80% by volume of the body and often constitutes approx. 78% by volume of the body, and wherein the silicon atom-containing binder is contained in a quantity of up to approx. 35% by volume of the body, which binder is distributed at least substantially uniformly throughout the polycrystalline diamond body, wherein the portion or surface of the binder which contacts the surfaces of the bound crystals is at least substantially silicon-35. carbide, ie at least 85% by volume and preferably 100% by volume of the portion or surface of the binder in direct contact with the surfaces of the diamond crystals is silicon carbide. The present diamond body is pore-free or at least practically pore-free.

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The amount of silicon carbide and silicon in the binder medium of the present diamond body may vary depending upon the degree of reaction between the surfaces of the diamond crystals and the inset silicon, and on the reaction between the elemental, non-diamond carbon and inset silicon phase. All else being equal, the actual amount of silicon carbide in the binder depends largely on the particular hot pressing temperature used and on the time during which this temperature is maintained. In particular, the content of silicon carbide increases as time and / or temperature increase. The method of milling the present body of bonded diamond crystals with a certain desired content of silicon carbide with e.g. the purpose of obtaining certain desirable properties can be determined empirically. Specifically, the binder may vary in composition from a detectable amount of silicon carbide to a detectable amount of pure silicon, where by a detectable amount of silicon carbide or pure silicon is meant an amount detectable by selective surface diffraction analysis. ) by transmission electron microscopy of a thin section of the present body. Generally, however, the present binder is essentially silicon carbide in amounts ranging from about 2% by volume to approx. 30% by volume of the present polycrystalline diamond body and of pure silicon in amounts ranging from approx. 33% by volume to approx. 5% by volume of the body. In addition, the diamond content of the present body is between ca. 65% by volume and no more than approx. 80% by volume of the body volume.

Selective surface diffraction analysis by transmission electron microscopy of a thin section of the polycrystalline diamond body will also show that at least a significant amount of silicon carbide in contact with the 30 diamonds bonded surfaces.

The present body of bound diamond crystals is devoid of voids or pores or at least practically pore-free, i.e. it may contain voids or pores in an amount of less than 1 35% by volume of the body, provided that such voids or pores are small; less than 0.5 µm, and sufficiently evenly distributed throughout the body, so that they have no significant deteriorating effect on its mechanical properties. The content of voids or pores in the present body can be determined by standard metal log

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11 nicks, such as optical examination of a polished cross section of the body.

The present diamond body is also devoid of a phase of elemental, non-diamond carbon in that it contains no phase of non-diamond carbon in amounts detectable by X-ray diffraction analysis.

When the present process is carried out with the silicon and dlamant crystal mass present as layers superimposed on each other, the resulting product may have at least one surface surface and may be available in a number of different forms, e.g. a slice, cube or rectangle, rod or rod.

When the present process is carried out with the silicon present as a tube or cylinder with a core or through hole and with the diamond portions of the cores packed into the core, the silicon seeps in during hot pressing through the core of compressed diamond crystals and provides the present diamond body with the shape of a rod. with circular cross section.

When the present process is carried out with a silicon rod located centrally in the cavity and the space between the silicon rod and the cavity wall is packed with diamond crystals, the silicon seeps in through the surrounding mass of diamond crystals and provides the present diamond body with the shape of a tube or hole. cylinder.

A particularly advantageous feature of the present invention is that the present polycrystalline diamond body can be provided in many different sizes and shapes. Eg. For example, the present body may be as wide or as long as 25 mm or more. Polycrystalline diamond bodies of 25 mm or more in length and with the present diamond density can, due to the limitations of the device necessary to withstand the high pressure temperature requirements for the required time, ie. the device is so complex and massive that its capacity is limited, in practice it is not produced or cannot be produced at all by methods utilizing the ultra high pressure and temperature for the diamond stability range. On the other hand, the present polycrystalline diamond body can be made as small or as thin as desired, but it will always be on more than one monolayer of diamond crystals.

Part of the present diamond body may be soldered, brazed or otherwise secured to a suitable support material which

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eg. sintered or hot pressed silicon carbide, sintered or hot pressed silicon nitride or cemented carbide or a metal such as e.g. molybdenum, which constitutes a tool insert such as e.g. can be held by a tool shank suitable for holding in a machine tool, and thereby the exposed surface of the diamond body can be used for direct machining. Alternatively, the present diamond crystal body may be mechanically clamped to a swivel steel so that direct machining can be achieved with the exposed surface of the diamond body.

The invention will be further described by the following example.

Example

The apparatus used in this example was substantially similar to that shown in Figures 1, 2 and 3.

Hexagonal boron nitride having a size p from approx. 2 pm to approx. 20 µm was packed in a die and a cylinder used as a mold was pressed into the powder as shown in Figure 1 at 19a and 9.

The cylinder was made of sintered metal carbide (cement: 20-oct metal carbide) and was approx. 8.89 mm in diameter and 6.35 mm thick. The axis of the cylinder aligned with the central axis of the matrix.

In this embodiment, unlike Figure 1, after the cylinder was inserted into the powder, an additional amount of hexagonal boron nitride powder was placed in the matrix so that the cylinder was completely covered and the provided powder enclosed cylinder was pressurized at room temperature at 3450 bar overpressure (50,000 psi). The piston 23a was then retracted and the piston 23 was used to push the provided, pressed, powder-enclosed cylinder partially out of the die. The exposed portion of the pressed powder was removed so that the cylinder was partially exposed. The cylinder was then removed leaving the cavity 11 as it had pressed therein.

A slice of silicon weighing 140 mg and of the same diameter as the inner diameter of the cavity was placed at the bottom of the cavity. Ca.

35 250 mg size graded diamond powder with diamond sizes of approx. 1 pm to approx. 60 pm and thereof approx. 40 weight percent less than 10 µm was packed on top of the silicon wafer.

A disc of hot pressed hexagonal boron nitride powder of the same diameter as the inner diameter of the cavity is placed in the cavity on top of

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13 diamond powder, thereby ensuring that the surface of the resulting polycrystalline diamond body would be flat.

The entire mass was then pushed into the center of the die by means of the plunger 23a, which was then withdrawn. An additional 5 amounts of hexagonal boron nitride powder were placed in the matrix to cover the hot pressed disc of hexagonal boron nitride, so that the cavity and its contents were enclosed in hexagonal boron nitride, as shown at 19 in Figure 2. The charge obtained was then pressed at room temperature. i.e. cold press, in the steel matrix under a pressure of 10 µl 5520 bar overpressure (80,000 psi), as shown in Figure 2, with the cavity and its contents being applied at practically isostatic pressure until the pressure stabilized, thereby forming one with respect to dimensions stabilized, shaped, practically isostatic system of powder-contained cavity as well as content. From previous Experiment 15, it was known that the diamond crystal density in the provided pressed assembly of elements, i.e. in the formed, practically isostatic system of powder-encapsulated hollowness and content, the diamond crystal density was greater than 75% by volume of the compacted diamond mass. The amount of silicon present was approx. 40% by volume of the compacted diamond mass.

The provided pressed assembly of elements 21 consisting of the powder enclosed cavity and contents was then hot pressed, i.e. it was pressed into a graphite form of the same diameter size as the steel matrix as shown in Figure 3 and placed in an induction heater. The interior of the cavity was evacuated and a nitrogen atmosphere was passed in, evacuating the heater to approx. 1330 Pa (10 torr) before being refilled with a stream of dry nitrogen. A pressure of approx. 345 bar overpressure (5,000 psi) was applied to the pressed assembly of elements 21 and maintained by the graphite matrix, which was then heated by the induction heater to a temperature of 1500 ° C for 7 minutes. At this heating, the pressure reached approx. 690 bar overpressure (10,000 psi) due to the entire system expansion.

At 1500 ° C the plunger 23a sank and the pressure dropped to approx. 345 bar overpressure (5,000 psi), indicating that the silicon had melted and become liquid and seeped into the diamond mass. The pressure was raised until it was again 690 bar overpressure (10,000 psi) and, to ensure that the silicon was completely seeped into the diamond mass, was kept

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14 p in this value for 1 minute at 1500 ° C. The energy supply was then interrupted, but no further pressure was imposed. This provided a fixed pressure at high temperature but lower pressure at lower temperature, thereby providing adequate geometric stability. At room temperature, the generated crystal crystal lined diamond body was uncovered.

After removal of surface shells of hexagonal boron nitride powder, the integral polycrystalline diamond body disc provided had a diameter of 8.89 mm and a thickness of 10 µm | 1.27 mm.

The polycrystalline slice had practically smooth, flat surfaces and had apparently been well penetrated by binder. Optical examination of the disc magnified 100X in a microscope showed that it was pore-free.

15 Using a hammer and a wedge, the disc was fractured, so to speak, in the middle. Examination of the fractured cross-sectional surfaces of the disc revealed that the fracture or fracture was trans-granular rather than intergranular, ie. it was fractured through the diamond grains rather than along the grain boundaries. This 20 shows that the binder was strongly adherent and that it was as strong as the diamond grains themselves or the diamond crystal clays. Likewise, the fractured surfaces were pore-free and the binder was evenly distributed throughout the body.

A fracture surface perpendicular to the disc was polished on a cast-iron diamond polishing apparatus. Examination of the polished surface showed no rows of holes formed by extraction of diamond fragments, showing the strong bonding therein and its utility as abrasive. The polished cross section is shown in Figure 4.

The diamond density was determined to be approx. 72% by volume of the 30 slice. The diamond density was determined by standard point counting technique using a micrograph of the polished fracture surface enlarged 690X, and the surface area examined was large enough to represent the entire body microstructure.

X-ray diffraction analysis of the crushed body revealed that it comprised diamond, silicon carbide and pure silicon, and that the silicon carbide and pure silicon constituted at least 2% by volume of the body. However, the X-ray diffraction analysis of the crushed body did not detect any phase of free, non-diamond carbon.

Claims (11)

1. A polycrystalline diamond body, especially in the form of a disc, rod or hollow cylinder comprising a mass of diamond crystals, characterized in that the diamond crystals are bonded to each other with a silicon atom-containing binder constituted by silicon carbide and free silicon, the diamond crystals having a size of from 1 to 1000 µm, that the diamond crystal density in the body is in the range of from 65 to at most 80% by volume of the body, that the proportion of 10 silicon atom-containing binder constitutes up to 35% by volume of the body, that the binder is distributed substantially equally in the body, that the proportion of the binder in contact with diamond surfaces consists essentially of silicon carbide and that the diamond body is substantially pore-free. A polycrystalline diamond body according to claim 1, characterized in that the density of the diamond crystals is from 65 to 78% by volume of the body. Polycrystalline diamond body according to claim 1 or 2, characterized in that the diamond crystals are sized and range from 1 to 60 µm. Polycrystalline diamond body according to any one of claims 1-3, characterized in that silicon carbide is present in an amount of pi from 2 to 30% by volume of the body. Process for producing a polycrystalline diamond body according to any one of claims 1-4 and using a hot pressing step, characterized in that: a) in a pressure transmitting powder medium which transmits an applied pressure substantially undiminished, and which remains substantially non-sintered during the heat pressing, a cavity is extruded; b) a cavity is placed in this cavity and a mass of diamond crystals in contact with the silicon mass; c) the cavity and its contents are covered with an additional amount. of the pressure transmitting powder medium and thereby being enclosed by the pressure transmitting powder medium; d) applying to the cavity and its contents a substantially isostatic pressure to substantially completely equilibrate the dimensions of the cavity and its contents, thereby producing a mold. DK 154824 B stable, essentially isostatic system of powder-enclosed cavity and content, the density of diamond crystals constituting more than 65% by volume of the resulting compacted diamond crystal mass, and silicon is used in an amount sufficient to fill the gaps in the compacted diamond crystal mass, e) subjecting the resulting substantially isostatic system to hot pressing. producing liquid silicon and introducing it into the spaces of the compressed diamond crystal mass at a temperature of from the temperature at which silicon becomes liquid and up to 1600 ° C under a pressure sufficient to cause the liquid silicon to penetrate into the spaces of the compacted diamond crystal mass, with less than 5% by volume of the diamond crystals upon hot pressing being converted to free, non-diamond-shaped carbon, and non-diamond-shaped carbon or the surfaces of the diamond crystals reacting with silicon to form 20 of silicon carbide, f) that while cooling off the hot-pressed, substantially isostatic system maintains sufficient pressure to maintain at least substantially the dimensions of the hot-pressed system, and 25 g) remove the formed crystalline diamond body in which the body of the diamond crystals is bonded to each other with a silicon atom-containing binder. of silicon carbide and silicon, and the diamond crystals are present in an amount of at least 65% by volume of the body. Process according to claim 5, characterized in that the diamond crystals are sized and have a size of from 1 to 60 µm. Process according to claim 5 or 6, characterized in that the silicon is used in an amount of from 25 to 60% by volume calculated on the basis of the volume of the compacted diamond crystal mass. Process according to any one of claims 5-7, characterized in that a compacted diamond crystal mass with a density of diamond crystals of up to 85% by volume of the volume of the compressed crystals is produced. Process according to any one of claims 5-8, characterized in that the silicon mass is provided in the form of a layer, on top of which the diamond crystal mass is placed in the form of a second layer. Method according to claims 5-8, characterized in that the silicon mass is provided in the form of a rod substantially in the middle of the cavity and the diamond crystal mass is introduced into the space between the silicon rod and the wall of the cavity. Process according to any one of claims 5-8, characterized in that the silicon mass is provided in the form of a hollow cylinder and that the inner space enclosed by the hollow cylinder is filled with the diamond crystal mass. 15 20 25 30 35