CH644090A5 - POLYCRYSTALLINE DIAMOND BODY AND METHOD FOR PRODUCING THE SAME. - Google Patents

Description

The invention relates to a polycrystalline diamond body made of a dense mass of diamond crystals which are connected to one another by a binder containing silicon atoms. The invention further relates to a method for producing a polycrystalline diamond body of the aforementioned type.

In the process for producing a polycrystalline diamond body, in which the diamond crystals are

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Binder containing licium atoms are connected to one another, pressures are applied which are substantially lower than the pressures in the diamond-stable region of the state diagram of carbon. The polycrystalline diamond body can be manufactured in various shapes and sizes and is suitable as an abrasive, cutting tool, nozzle or as an abrasion-resistant component.

The polycrystalline diamond body according to the invention with a mass of diamond crystals is characterized in claim 1, a process for the production of said diamond body in the preceding claim 8.

In the method according to the invention for producing a polycrystalline diamond body, hot pressing is therefore carried out: First, a mold cavity of a predetermined size is pressed into a powder medium suitable for pressure transfer at ambient temperature under a pressure which is sufficient to bring the powder into an essentially stable shape. The powder medium transmits the applied pressure essentially undiminished and remains essentially unsintered even during hot pressing. A silicon mass and a mass of diamond crystals in contact with it are placed in the cavity. The cavity and its contents are then covered with additional powder medium, so that the cavity is then enclosed by the powder suitable for pressure transmission. An essentially isostatic pressure is then exerted on the cavity and its contents via the powder medium, which is sufficient to stabilize the dimensions of the cavity and its contents substantially uniformly, thereby creating a solidified, essentially isostatic system of the cavity encased in powder. Silicon is used in an amount sufficient to fill the gaps in the compressed diamond crystal mass. The isostatic system, including the cavity and its contents, is now exposed to an atmosphere which is essentially neutral towards the diamond crystals and silicon during the subsequent hot pressing. When the essentially isostatic system is hot pressed, silicon becomes liquid and penetrates into the interstices present in the compressed diamond crystal mass. In hot pressing, the isostatic system is brought to a temperature which ranges from the temperature at which silicon becomes liquid up to 1600 ° C. and is subjected to a pressure which is sufficient to wash the liquid silicon into the interstices of the compressed diamond crystal mass. During hot pressing, less than 5% by volume of the diamond crystals are converted into non-diamond-shaped elemental carbon, this non-diamond-shaped carbon or the surface of the diamond crystals reacting with silicon to form silicon carbide. In the subsequent cooling of the hot-pressed isostatic system, the system is kept under a pressure which is sufficient to substantially maintain the dimensions of the hot-pressed system. Finally, the formed polycrystalline diamond body is removed, consisting of diamond crystals bound by a silicon-containing binder comprising silicon carbide and silicon, and in which the diamond crystals are present in a proportion of at least 65% by volume of the total volume of the body .

The invention will now be explained in more detail with reference to drawings, in which:

1 shows a section through a device for molding a cavity into a pressure-transmitting powder medium,

2 shows a section through a device for applying isostatic pressure to a cell comprising the cavity and its contents via a pressure-transmitting powder medium, the dimensions of the cell being stabilized with the formation of an essentially isostatic system,

Fig. 3 shows a section through a graphite mold with the enclosed cell for the simultaneous application of heat and pressure to the essentially isostatic system and

4 shows a photograph with a 690 magnification of a polished cross section of a diamond body produced by the method of the invention with a diamond content of 72% by volume; the phase that appears gray-white in FIG. 4 is the binder and the gray phase is diamond.

In carrying out the method according to the invention, a diamond crystal mass in contact with a silicon mass is subjected to cold pressing at ambient temperature or room temperature for the purpose of shape stabilization and then to a hot pressing in which the diamond crystal mass is impregnated with the silicon.

The diamond crystal mass and the silicon mass can have a number of shapes. For example, each mass can have the shape of a layer, the two layers being arranged one above the other. The silicon mass can also be arranged in the form of a hollow cylinder, in which case the interior of the hollow cylinder is filled with diamond crystals. In another embodiment, the silicon can be arranged in the form of a block or a rod in the center of the mold cavity, in which case the remaining space between the silicon block or the silicon rod and the inner wall of the mold cavity is filled with diamond crystals.

Both natural and synthetic diamond crystals can be used in the method according to the invention. The size of the diamond crystals used has a size in the range from approximately 1 to approximately 1000 micrometers, the crystal size or the crystal sizes largely depending on the desired packing density of the diamond crystals and also on the intended use of the diamond body. In any case, crystals with a size of less than 5 micrometers must be mixed with crystals with a size of more than 10 micrometers, and the proportion of crystals with a size of less than 5 micrometers should preferably not exceed 50% by volume of the diamond mass, so that silicon can be washed into the diamond mass to a sufficient extent. If the diamond body to be produced is to be used for grinding purposes, diamond crystals with a size of not more than 60 micrometers are preferably used. In order to optimize the packing of the diamond crystals in the diamond mass, the diamond crystals should preferably be graded in size and therefore should be in a particle size range comprising small, medium and large crystals. The size-graded crystals are preferably in the particle size range from 1 to 60 micrometers, with within this range preferably from 60 to 80% by volume of the total crystal mass, a particle size lying in the upper part of the particle size range and 5 to 10% by volume in the middle range of the particle size range and the rest have a particle size in the lower part of the particle size range.

The corresponding grain composition of the diamond crystals can be achieved by reducing the size of larger diamond crystals in a jet mill. Preferably

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diamond crystals are chemically cleaned to remove surface oxides or other contaminants before being used in the method of the invention. For cleaning, the diamond crystals can be heated in hydrogen at about 900 ° C for about an hour.

In the method according to the invention, the silicon is introduced into the pores or spaces between the diamond crystals. The silicon, for example in solid or powder form, is used in an amount sufficient to fill the pores or interstices of the diamond crystal mass, which has a diamond crystal content of over 65% by volume of the total body. In general, silicon can be used in an amount in the range of approximately 25 to 80% by volume, but for optimal results in an amount in the range of 30 to 60% by volume, based on the volume of the diamond crystal mass.

The hot pressing is carried out in an atmosphere which has no noticeable harmful influence on the properties of the diamond crystals or the infiltrating silicon. The hot pressing is carried out in particular under vacuum or in an inert gas such as argon or helium or else under nitrogen or hydrogen. The hot pressing is carried out sufficiently quickly that there is no noticeable reaction between the liquid silicon and nitrogen or hydrogen. Hot pressing cannot be carried out in air, since diamond graphitizes quickly at over 800 ° C and liquid silicon would be oxidized to silicon dioxide before a noticeable amount of liquid silicon would have been washed into the diamond mass.

The hot pressing is carried out in a temperature range that begins at the temperature at which silicon becomes liquid and extends to 1600 ° C. The pressure applied at the hot pressing temperature only has to be sufficient to tear stubborn boundary layers in the diamond mass, which prevent the penetration of liquid silicon into the pores of the diamond mass. This usually requires a minimum pressure of approximately 35 kg / cm 2. The hot press pressure can range in particular from about 35 to 1400 kg / cm 2, but is usually in the range from about 70 to about 700 kg / cm 2. Hot pressing pressures of over 700 kg / cm2 bring no noticeable advantage. Likewise, temperatures above 1600 ° C do not bring any noticeable advantage; rather, at temperatures above 1600 C, the diamonds can become too graphitized.

A temperature at which silicon becomes liquid means the temperature at which the silicon is able to flow easily. If silicon is at its melting temperature, which is given in the literature in the range from approximately 1412 to approximately 1430 ° C., it has a high viscosity. With increasing temperature, however, the silicon becomes less viscous and finally becomes liquid at a temperature approximately 10 ° above the melting point. The temperature at which silicon is liquid is the temperature at which silicon penetrates into the capillary-like channels, spaces or pores of the diamond crystal molding compound. If the temperature is increased still further, the fluidity of the liquid silicon is increased still further, so that the liquid silicon then penetrates the diamond crystal molding compound even faster. At the maximum hot pressing temperature of approximately 1600 ° C, the liquid silicon has the highest fluidity and therefore penetrates the crystal mass at the highest speed.

In the arrangement shown in FIG. 1, a cavity of a predetermined size is pressed into a pressure-transmitting powder medium 19a with the aid of a pressing tool 9. A sufficient pressure, which is usually in the range from approximately 700 to approximately 3500 kg / cm 2, is exerted by the press ram in order to at least bring the powder 19a into a stable shape, so that after pressure relief, i.e. H. after lifting the punch 23a, the pressing tool 9 can be removed and the cavity 11 pressed in by the pressing tool remains. The pressing tool 9 consists of a suitable pressure-resistant material, for example stainless steel or sintered hard metal, and has a smooth surface, so that after the pressing tool is pulled out of the compressed powder, the cavity 11 pressed in by the pressing tool remains. After pulling back the pressing tool 9 in the arrangement according to FIG. 1, a disk 12 made of silicon and a mass of diamond crystals are arranged in contact with the silicon within the pressed-in cavity 11. In order to ensure that the diamond crystal mass has the desired thickness for the polycrystalline body, the cavity 11 should be dimensioned such that no space remains after the introduction of the silicon and the diamond crystal mass. In the cold press now following to stabilize the shape of the system, diamond crystals would be displaced into the available free space and the desired shape of the diamond body would thereby be impaired. Additional pressure-transmitting powder is then arranged over the cavity filled with silicon and diamond crystals, whereby the powder-enclosed cell 10 shown in FIG. 2 is formed, in which the content given in the cavity is located.

The cell 10 is then cold pressed in the manner shown in FIG. 2 at room temperature or ambient temperature. It is only necessary to use a pressure sufficient to form a dimensionally stable, essentially isostatic system. It can be seen from FIG. 2 that the cell 10 located within the cylindrical core of a press mold 20 is enclosed by a powder medium 9 which transfers pressure. The pressure-transmitting powder medium consists of very fine particles, preferably with a sieve size of less than 160 mesh / cm. The pressure-transmitting powder medium remains essentially unsintered under the pressure and temperature conditions of the present process and is essentially inert to liquid silicon. Powdered hexagonal boron nitride and powdered silicon nitride are particularly suitable as the pressure-transmitting powder medium. The pressure-transmitting powder medium ensures that an essentially isostatic pressure is exerted on the cell 10, as a result of which the cell 10 and its contents are substantially uniformly stabilized with regard to their dimensions, i. H. is compacted, so that an essentially isostatic system of corresponding shape is formed, which contains the cell enclosed by the powder, in which the density of the resulting compressed diamond crystal layer is over 65% by volume of the volume of the compressed crystals. The press mold 20 (ring 22 and press ram 23, 23a) can consist of tool steel, the ring 22 optionally being provided with a cemented carbide bushing 22a in order to use pressures of up to 14,000 kg / cm 2 in the cold pressing shown in FIG. 2 to enable. Pressures over 14,000 kg / cm3 have no noticeable advantage. Within the area enclosed by the press ram 23, the sleeve 22a and the press ram 23a, pressure is preferably in the range of

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1400 to 7000 kg / cm 2 and usually up to 3500 kg / cm 2 are exerted on the pressure-transmitting medium by the press rams, if these are operated in a conventional manner, until the applied pressure has stabilized in the manner known from powder metallurgy.

In particular, the pressure used in cold pressing is determined empirically. Increasing the pressure above the pressure value that provides a dimensionally stable, substantially isostatic system does not result in additional compression or dimensional stabilization of the cell 10 and its contents.

A powder medium that transmits the pressure, for example, pressure exerted on hexagonal boron nitride and silicon nitride in an axial direction, approximately produces a hydrostatic pressure effect, so that an essentially isostatic pressure acts on the entire cell, i. H. the cell is subjected to the same pressure from all sides. It is believed that the pressure applied is transmitted to the cell 10 substantially unabated. During cold pressing, the size of the cavities between the crystals is reduced, so that capillary-like pores are optimally formed in the diamond mass. Furthermore, the diamond crystal mass is brought to the required density of over 65% by volume. This reduction in the void volume also results in a reduction in the content of non-diamond-shaped material finally present in the diamond body and results in more closely opposing crystal surfaces which can be effectively connected to one another.

After cold pressing, the density of the compressed diamond crystals in the cell should be over 65% by volume of the volume of the crystals. Often the diamond density of the compressed diamond crystals can range from about 66 to less than about 85% by volume of the compressed diamond crystals. The higher the density of the compressed crystal mass, the lower the proportion of non-diamond-shaped material that gets between the crystals, so that a correspondingly harder diamond body is also produced.

The essentially isostatic system 21 of the powder-coated cell formed by cold pressing is then hot pressed, the system being subjected to the hot pressing temperature and the hot pressing pressure simultaneously.

After the cold pressing, one of the two press punches 23 or 23a is withdrawn and the essentially isostatic system 21, which is now in the form of a compact molded body, is removed from the sleeve 22 and converted into the graphite mold shown in FIG. 3, which has a hole with the same diameter as the sleeve 22a has. The transferred system 21 is then enclosed within the hole 31 between graphite dies 32 and 32a. To display the temperature of the dimensionally stabilized, essentially isostatic system 21, the graphite mold 30 is provided with a thermocouple 33. The graphite mold 30 with the system 21 enclosed is then placed in a conventional hot press furnace (not shown). The furnace chamber is at least substantially evacuated, which also causes the system 21 including the cell 10 to be evacuated, so that the system 21 and the cell 10 are essentially under a vacuum in which the hot pressing can be carried out. Optionally, nitrogen or hydrogen or an inert gas such as argon can also be introduced into the furnace chamber in order to expose the system 21 located in the furnace chamber, including the contents of the cell 10, to an atmosphere suitable for hot pressing. While the graphite stamps 32 and 32a exert a hot-pressing pressure acting on the system 21 in the axial direction, the temperature of the system is increased to the hot-pressing temperature at which the silicon wafer 12 is liquid.

With hot pressing, the hot pressing temperature should be reached as quickly as possible. The hot pressing temperature is usually maintained under the hot pressing pressure for at least one minute to ensure adequate soaking of the diamond crystal mass. Usually a hot pressing time in the range of about 1 to about 5 minutes is sufficient. Since the conversion of diamond into non-diamond-shaped elemental carbon largely depends on the time and temperature and in particular the higher the temperature and the higher the temperature, the greater the likelihood of conversion into non-diamond-shaped elemental carbon, the hot pressing must be carried out before 5 vol .-% diamond are converted into non-diamond elemental carbon. The extent of the conversion can be determined empirically. If 5 or more% by volume of diamond is converted into non-diamond-shaped elemental carbon, a phase of non-diamond-shaped elemental carbon may remain in the end product, which could have an adverse effect on the mechanical properties of the end product.

The pressure exerted on the liquid silicon during hot pressing causes the slag, which is in the form of a difficult-to-melt layer, to be broken up, largely from oxide but also from carbide, which is usually present or formed between liquid silicon and the diamond surfaces, so that the capillary pore system thereby is opened and then the liquid silicon penetrates into the pore system due to capillary action. Experiments have shown that the silicon does not seep into the diamond mass if, when the system 21 is hot pressed, a pressure is exerted and maintained with the silicon in the liquid state which is insufficient to break up the slag.

When the silicon becomes liquid, any slag that may be present or formed floats in the silicon and remains behind when the liquid silicon penetrates the compacted diamond mass. The diamond body thus formed does not contain a glass-like phase which would prevent the formation of a firm bond between diamond and the binder containing silicon atoms.

If, during hot pressing, the liquid silicon penetrates and penetrates the diamond mass, the liquid silicon envelops the surfaces of the compressed diamond crystals and reacts with the diamond surfaces or possibly arising elemental, non-diamond-shaped carbon with the formation of silicon carbide on the surfaces of the diamond crystals, so that a one-piece diamond body with a firm bond.

It is particularly important that substantially isostatic conditions are maintained during hot pressing, so that when the silicon becomes liquid, the liquid silicon cannot escape between the diamond mass 13 and the cavity 11 and escape to a significant extent, but rather is forced into the diamond crystal mass 13. The portion of the pressure-transmitting powder closely related to the contents of the cavity, i. H. the portion of the powder that preferably extends outward from the inner wall of the cavity or from the cell to approximately 25 mm should not have interconnected pores larger than about 5 microns in size to prevent excessive leakage.

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liquid silicon during hot pressing can be prevented.

After the end of the hot pressing, at least such a pressure should be maintained during the cooling of the hot-pressed system 21 that an isostatic pressure acting on the cell 10 in the system 21 when cooling substantially sufficient to maintain its dimensional stability. The hot-pressed system 21 is preferably allowed to cool to room temperature and the diamond body formed is then removed. Squeezed out excess silicon can be removed from the surface of the polycrystalline body formed in a conventional manner, for example by grinding.

The polycrystalline diamond body produced according to the invention contains diamond crystals which are firmly connected to one another by a binder containing silicon atoms, which consists essentially of silicon carbide and elemental silicon. The diamond crystals are from about 1 to about 1000 microns in size. The diamond density, i.e. H. the proportion of diamond in the polycrystalline body ranges from about 65 to about 80% by volume and is often about 78% by volume. The polycrystalline diamond body contains up to about 35% by volume of binder containing silicon atoms, which is at least substantially uniformly distributed in the polycrystalline diamond body. The part of the binder which is in contact with the surfaces of the diamond crystals consists at least in a substantial amount of silicon carbide, i. that is, at least about 85 and preferably 100% by volume of the portion of the binder in direct contact with the surfaces of the diamond crystals is silicon carbide. The polycrystalline diamond body is pore-free or at least essentially pore-free.

The proportion of silicon carbide and silicon in the binder of the polycrystalline body can vary more or less depending on the extent of the reaction between the surfaces of the diamond crystals and the penetrating silicon and between non-diamond-shaped elemental carbon and penetrating silicon. Assuming that all other factors are the same, the amount of silicon carbide present in the binder depends primarily on the hot pressing temperature used and the length of time within which the applied hot pressing temperature has been maintained. The silicon carbide content of the binder increases with increasing hot pressing temperature and / or time. It is therefore possible, for example, to determine empirically the process conditions which must be observed in order to achieve a polycrystalline diamond body with a certain silicon carbide content. The composition of the binder can vary within a wide range, so that on the one hand only a detectable amount of silicon carbide and on the other hand only a detectable amount of elemental silicon can be present. The amount that can be detected means the amount that can be detected with an electron microscope when a thin part of the diamond body is irradiated due to the electron beam diffraction that occurs. In general, however, the binder consists essentially of silicon carbide in an amount of about 2 to about 30% by volume, based on the volume of the polycrystalline diamond body, and of elemental silicon in an amount of about 33 to about 5% by volume. based on the volume of the polycrystalline diamond body. The diamond content of the polycrystalline diamond body is usually in a range from about 65% by volume to slightly less than 80

Vol .-%, based on the volume of the diamond body, extends.

With the help of an electron microscope, when a thin section of a polycrystalline diamond body is irradiated, it can be determined due to the electron beam diffraction that at least a substantial proportion of the part of the binder which is in contact with the surfaces of the diamond crystals consists of silicon carbide.

The polycrystalline diamond body according to the invention is pore-free or at least substantially pore-free, i.e. that is, it can contain voids or pores in an amount of less than 1% by volume, based on the volume of the body, provided the pores or voids are small (less than 0.5 microns) and sufficiently evenly distributed in the body, so that they have no appreciable adverse effect on the mechanical properties of the body. "The void or pore content of the polycrystalline diamond body according to the invention can be determined by conventional metallographic methods, for example optically by observing a polished section of the body.

The polycrystalline diamond body according to the invention is also free of elemental, non-diamond-shaped carbon, i. that is, it contains no amount of elemental, non-diamond carbon detectable by X-ray diffraction analysis.

If silicon and the diamond crystals are used in the form of layers arranged one above the other in the method according to the invention, the diamond body formed has at least one flat surface and can have a number of shapes, for example the shape of a disk, a square, a rectangle, a rod or of a block.

If the silicon in the form of a tube or hollow cylinder is used in the implementation of the method according to the invention, the interior of which is packed with diamond particles, the liquid silicon penetrates during hot pressing into the core consisting of compressed diamond crystals, whereby a diamond body in the form of a cylinder with a circular shape Cross section arises.

If in the process according to the invention the silicon is used in the form of a rod which is arranged in the middle of the cavity and the space between the rod and the cavity wall of the mold is filled with diamond crystals, then the liquid silicon penetrates into the silicon rod during hot pressing - Send in diamond crystal mass, so that a diamond body is created in the form of a hollow cylinder.

A particular advantage of the invention is therefore that polycrystalline diamond bodies with different dimensions and shapes can be produced. For example, the diamond body can have a width or length of 25 mm or more. Polycrystalline diamond bodies which have a length of 25 mm or more and have a diamond content corresponding to the diamond content of a polycrystalline body according to the invention can practically not be produced by processes in which pressure and temperature conditions lying in the diamond-stable region of the state diagram of carbon come into use because the equipment required to generate and maintain such high pressure and temperature conditions requires an extraordinarily complex structure and therefore only have a limited capacity. On the other hand, polycrystalline diamond bodies according to the invention can also be extremely thin down to one

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Layer thickness of only one diamond crystal layer can be produced.

A polycrystalline diamond body according to the invention can be fixed by soft soldering, brazing or in some other way on a suitable base, for example made of sintered silicon carbide, sintered silicon nitride, sintered hard metal or a metal such as molybdenum, to form a tool insert. The tool insert thus formed can be attached to a suitable tool shaft for use as a cutting tool in a machine tool. However, a polycrystalline diamond body according to the invention can also be mechanically clamped on a tool holder and used as a cutting tool.

The invention is further explained using an exemplary embodiment.

Embodiment

Devices of the type shown in Figs. 1, 2 and 3 were used.

Powdered hexagonal boron nitride with a particle size of about 2 to about 20 microns was packed into a die, and a press tool in the form of a cylinder was pressed into the powder filling, as shown in Fig. 1 by reference numerals 19a and 9.

The cylinder used as the pressing tool was made of cemented carbide and had a diameter of approximately 9 mm and a length of approximately 6 mm. The cylinder was arranged so that its axis approximated the central axis of the die.

After inserting the cylinder into the powder, in contrast to FIG. 1, additional powdery hexagonal boron nitride was added to the die and the cylinder was completely covered with powder. The die filling with the cylinder enclosed by the powder was then pressed together at room temperature with a pressure of 3500 kg / cm2. The press ram 23 was then withdrawn, and the press ram 23 partially ejected the formed compact with the cylinder enclosed by the powder from the die. The exposed part of the pellet was then removed, thereby partially exposing the cylinder. The cylinder was then pulled out, leaving a corresponding mold cavity.

A silicon wafer weighing 140 mg and having the same diameter as the inside diameter of the mold cavity was placed on the bottom of the mold cavity. About 250 mg of diamond powder with graded grain size was packed on the silicon wafer. The grain size of the diamond powder ranged from about 1 to about 60 microns, with about 40% by weight of the diamond powder having a grain size of less than 10 microns.

A disk made by hot pressing hexagonal boron nitride with the same diameter as the inside diameter of the mold cavity was placed on the diamond powder inside the mold cavity to ensure that a polycrystalline diamond body with a flat surface is formed.

The compact was then pushed into the center of the die by the punch 23a, which was then withdrawn. To cover the hexagonal boron nitride disk, further hexagonal boron nitride powder was then added to the die, thereby enclosing the mold cavity with its contents in hexagonal boron nitride, as is indicated in FIG. 2 by reference number 19. The now existing loading of the steel matrix was • at room temperature, i. H. cold, with a pressure of

5600 kg / cm2 pressed in the manner shown in Fig. 2, wherein an essentially isostatic, ie. H. pressure was applied evenly from all sides. The pressing pressure was maintained until it formed a dimensionally stable powder molding, i. H. of an essentially isostatic system of the mold cavity contents embedded in the powder. It was known from previous experiments that the compressed diamond mass in the powder molding formed had a diamond density of over 75% by volume and that silicon was present in an amount of about 40% by volume of the compressed diamond mass.

The formed powder body 21 together with its contents was then hot pressed. For this purpose, the powder molding 21 was introduced in the manner shown in FIG. 3 into a graphite mold with the same diameter as the steel die and the graphite mold together with the powder molding 21 was placed in an induction heating furnace. The induction heating furnace was evacuated to a pressure of approximately 10 torr and then filled with dry nitrogen. A pressure of approximately 350 kg / cm 2 was then exerted and maintained on the powder molded body in the graphite mold. The pressurized powder molded body 21 was then inductively heated to a temperature of 1500 ° C. in seven minutes. When heating up, the pressure rose to about 700 kg / cm2 due to the thermal expansion of the entire system.

At 1500 ° C the pressure dropped to about 350 kg / cm2. This drop in pressure indicates that silicon has melted and become liquid and penetrated the diamond mass. The pressure was increased again to 700 kg / cm 2 and maintained at this value for one minute at 1500 ° C. in order to ensure complete soaking of the diamond mass with silicon. The heater was then turned off but no additional pressure was applied. This ensured a high pressure at high temperature and a reduced pressure at low temperature and thus adequate geometric stability. The polycrystalline diamond body formed was removed at room temperature.

After removal of the hexagonal boron nitride powder adhering to the surface of the polycrystalline diamond body in the form of a scale, the diamond body had the shape of a disk with a diameter of approximately 9 mm and a thickness of approximately 1.25 mm.

The polycrystalline diamond disc had essentially smooth flat surfaces and appeared to be well penetrated by the binder. An optical inspection of the diamond wheel at 100 times magnification under a microscope showed that the polycrystalline diamond wheel was pore-free.

With the help of a hammer and chisel, the disk was essentially broken apart in half. An examination of the breaking points of the disk showed that the breaking surface ran across the crystals and not along the crystal surfaces. This indicates that the binding caused by the binder is very good and just as strong as the diamond crystals themselves. The fracture surfaces were free of pores and the binder was evenly distributed over the body.

A broken surface of the disc was polished on a cast iron block. The polished surface had no holes due to broken diamond particles, which indicates that there is a strong bond between the diamond particles and that the diamond body is suitable as an abrasive body. The polished surface is shown in Fig. 4.

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The diamond density of the disk was determined to be about 72% by volume, based on the volume of the disk. The diamond density was determined according to the standardized point counting method, using a micrograph with a 690-fold magnification of the polished cross-sectional area and the analyzed surface area being of a size representative of the microstructure of the entire body.

An X-ray diffraction analysis of the broken body showed that the body consists of diamond, silicon carbide and elemental silicon and that the proportion of silicon carbide and elemental silicon makes up at least 2% by volume of the body. In the X-ray diffraction analysis of the broken body, however, no phase consisting of elementary, non-diamond-shaped carbon was found.

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Claims (15)

644 090 2nd PATENT CLAIMS 1. A polycrystalline diamond body with a mass of diamond crystals, characterized in that the diamond crystals are bonded to one another by a binder comprising silicon carbide and elemental silicon containing silicon atoms, the diamond crystals have a size of 1 to 1000 micrometers, the proportion of diamond crystals in the body is in the range from 65 to 80% by volume of the total body, the proportion of the binder containing silicon atoms makes up up to 35% by volume of the total body, the binder is at least essentially evenly distributed in the body, the proportion of the binder which is in contact with the diamond surfaces consists at least essentially of silicon carbide and the diamond body is at least substantially pore-free. 2. Polycrystalline diamond body according to claim 1, characterized in that the proportion of diamond crystals is from 65 to 78% by volume of the total body. 3. Polycrystalline diamond body according to claims 1 and 2, characterized in that the diamond crystals have graded grain sizes in the range from 1 to 60 micrometers. 4. Polycrystalline diamond body according to claims 1 to 3, characterized in that silicon carbide is present in the binder in an amount of 2 to 30 vol .-% of the total body. 5. Polycrystalline diamond body according to claim 1, characterized in that the body has the shape of a disc. 6. Polycrystalline diamond body according to claim 1, characterized in that the body has the shape of a rod. 7. polycrystalline diamond body according to claim 1, characterized in that the body has the shape of a hollow cylinder. 8. A process for producing the polycrystalline diamond body according to claim 1 using a hot pressing process, characterized by the following process steps: a) a cavity is pressed into a pressure-transmitting powder medium which transmits the acting pressure essentially unreduced and remains essentially unsintered during the hot pressing process, b) a silicon mass and a mass of diamond crystals are placed in contact with the silicon mass within the cavity, c) the cavity and its contents are covered with an additional amount of the pressure-transmitting powder medium and thereby coated with the pressure-transmitting powder medium, d) an essentially isostatic pressure is exerted on the cavity and its contents via the powder medium, which is sufficient to stabilize the dimensions of the cavity and its contents substantially uniformly, thereby creating a solidified, essentially isostatic system of the cavity encased in powder and its contents create, the proportion of diamond crystals making up at least 65% by volume of the resulting compressed diamond body and the silicon mass being used in an amount sufficient to fill the gaps in the compressed diamond crystal mass, e) an atmosphere is created around the essentially isostatic system including the cavity and its contents, which does not cause any noticeable damage to the diamond crystals and the silicon mass during the hot pressing process, f) the resulting substantially isostatic system is subjected to hot pressing to produce liquid silicon and to introduce it into the interstices of the compressed diamond crystal mass, which is at a temperature in the range from the temperature at which silicon becomes liquid to up to 1600 ° C below a pressure is carried out which is sufficient to float the liquid silicon into the interstices of the compressed diamond crystal mass, less than 5% by volume of the diamond crystals being converted into non-diamond-shaped elemental carbon during hot pressing and the non-diamond-shaped carbon or the surfaces of the Diamond crystals react with silicon to form silicon carbide, g) during the cooling of the hot-pressed, essentially isostatic system, a pressure on the system is maintained which is at least substantially sufficient to maintain the dimensions of the hot-pressed system, and h) the polycrystalline diamond body is removed, in which the diamond crystals are replaced by a Binder made of silicon carbide and silicon containing silicon atoms are bonded to one another and the diamond crystals are present in a proportion of at least 65% by volume of the total body. 9. The method according to claim 8, characterized in that diamond crystals with crown sizes graded in the range from 1 to 60 micrometers are used. 10. The method according to claim 8, characterized in that the silicon mass is essentially elemental silicon. 11. The method according to claims 8, 9 and 10, characterized in that silicon is used in an amount in the range from 25 to 60% by volume, based on the volume of the compressed diamond crystal mass. 12. The method according to claims 8 to 11, characterized in that the proportion of the compressed diamond crystal mass is 65 to 80 vol .-% of the volume of the crystal body. 13. The method according to claim 8, characterized in that the silicon mass is used in the form of a layer, over which the diamond crystal mass is arranged in the form of a layer. 14. The method according to claim 8, characterized in that the silicon mass is arranged 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 cavity wall. 15. The method according to claim 8, characterized in that the silicon mass is arranged in the form of a hollow cylinder and the interior enclosed by the hollow cylinder is filled with the diamond crystal mass.