DE2845755C2 - - Google Patents

Description

The invention relates to a method for manufacturing of a polycrystalline diamond body corresponding to that Preamble of claim 1.

From US-PS 32 39 321 is a method of known type mentioned in the case of the diamond powder Silicon powder mixed and the resulting powder mixture in a high pressure apparatus initially high Press and then one to melt the silicon exposed to sufficient temperature. The pressure is at least 20 kilobars and ranges up to 76 kilobars.

From US-PS 39 13 980 is a method for manufacturing known a polycrystalline diamond body in which Diamond particles mixed with silicon particles and the mixture is then sintered under pressure. The pressure is 5 to 100 kilobars, and the sintering temperature lies in the range of the state diagram of coal material in which diamond is not thermally stable.

From GB-PS 13 07 713 is a method for manufacturing known a polycrystalline diamond body in which the diamond particles with a binder phase Silicon carbide powder are mixed and the powder mix then pressed under pressure and temperature conditions in which no graphitization of diamond occurs.

To carry out the known manufacturing processes of polycrystalline diamond bodies are therefore complex High pressure equipment required. With the known This means that only diamond bodies with a ratio can be used  produce moderately small dimensions economically.

The invention is based on the object of a method of the type mentioned at the beginning with which polycrystalline diamond body of various shapes and in different dimensions without great expenditure on equipment can be produced.

This task is solved by a procedure according to characterizing part of claim 1. expedient further formations of the method result from the subclaims.

The one used in the method according to the invention Pressure, especially the pressure exerted during the hot pressing process, is compared to the known high pressure processes relatively low, so that with the method according to Invention diamond body of larger dimensions simple and can be produced economically. The after Process according to the invention made diamond body can be used as grinding tools, cutting tools and abrasion-resistant components are used.  

The invention will now be described with reference to drawings explained in which show

Fig. 1 shows a section through a device for molding a cavity in a pressure-transmitting powder medium.

Fig. 2 shows a section through a device for applying isostatic pressure to the cavity and its contents cell comprising a pressure-transmitting powder medium,

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

Fig. 4 is a photograph with a magnification of a polished cross-section 690facher a by the method according to the invention diamond body produced with a diamond content of 72 vol .-%; the gray-white phase in Fig. 4 is the binder and the gray phase is diamond.

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

The diamond crystal mass and the silicon mass can have a number of shapes. For example, each Mass have the shape of a layer, the two Layers are arranged one above the other. The silicon mass can also be arranged in the form of a hollow cylinder be, with the interior of the hollow cylinder Diamond crystals are filled in. Another one  Embodiment can the silicon in the form of a block or a rod arranged in the middle of the mold cavity the remaining space between the silicon block or rod and the inner wall of the mold cavity is filled with diamond crystals.

In the method according to the invention, both natural and synthetic diamond crystals can also be used. The Diamond crystals used have towards their largest dimension a size in the range of 1 to 1000 microns, the crystal size or the crystal largely depend on the desired packing density of the Diamond crystals and also the purpose of the diamond body depend. However, crystals with a size of less than 5 µm with crystals larger than 10 µm are mixed, and the proportion of crystals with a Size below 5 µm should preferably not exceed 50 Vol .-% of the diamond crystal mass, so silicon sufficiently in the diamond crystal mass can be washed up. Should the diamond body to be manufactured are used for grinding purposes preferably diamond crystals with a size of not over 60 µm. To optimize the packing of the diamond crystals in the diamond crystal mass are the diamond crystals graded in size and therefore in a small, Particle size range covering medium and large crystals lie. Preferably, the graded are Crystals in the particle size range from 1 to 60 μm, preferably 60 to 80 within this range Vol .-% of the total crystal mass in the upper part of the Particle size range lying particle size, 5 to 10 Vol .-% in the middle of the particle size range lying crystal size and the rest one in the lower part of the particle size range.

The corresponding grain composition of the diamond crystals can be done by reducing the size of larger diamond crystals reach in a jet mill. Preferably the  Diamond crystals chemically cleaned to on the surface remove existing oxides or other impurities, before being used in the method according to the invention. For cleaning, the diamond crystals can be in hydrogen be heated at about 900 ° C for about an hour.

In the method according to the invention, the silicon is in the Pores or spaces between the diamond crystals leads. For example in solid or powdered form Form silicon is used in an amount that sufficient to cover the pores or spaces of the Diamond mass to fill in, which has a diamond content of over 65% by volume. Generally silicon can in an amount of 25 to 80 vol .-%, based on the Volume of the diamond crystal mass with a diamond content of over 65 vol .-%, are used.

The hot pressing is carried out in an atmosphere which have no noticeable harmful influence on the Properties of diamond crystals or oozing Has silicon. The hot pressing is done in an inert gas like argon or helium or even under nitrogen or carried out hydrogen. The hot pressing will performed sufficiently quickly so that no noticeable Reaction between the liquid silicon and nitrogen or hydrogen takes place. Hot pressing cannot be carried out in air since diamond at over 800 ° C quickly graphitized and liquid silicon to silicon would oxidize before a significant amount of dioxide liquid silicon washed into the diamond crystal mass would have been.

The hot pressing is carried out in a temperature range leads, which begins at the temperature at which silicon becomes liquid, and reaches up to 1600 ° C. The one at the hot press temperature applied pressure must only be sufficient to stubbornly tear open boundary layers in the diamond mass,  the penetration of liquid silicon into the pores the diamond mass prevented. This is usually a Minimum pressure of 35 bar required. The hot press pressure ranges from 35 bar to 1400 bar, but is usually in the Range from 70 to 700 bar. Hot pressures of over 700 bar bring no noticeable advantage. Bring likewise Temperatures above 1600 ° C are not a noticeable advantage, rather can be too strong at temperatures above 1600 ° C Graphitization of the diamonds occur.

Silicon is at its melting temperature, for which in the literature the range from 1412 to 1430 ° C. it has a high viscosity. With increasing Temperature, the silicon becomes liquid.

In the arrangement shown in Fig. 1, a cavity of a predetermined size is pressed into a pressure-transmitting powder medium 19 a with the help of a press tool 9 . In this case, exerted by the press ram, a sufficient pressure is usually in the range of 700 to 3500 bar, in order to bring the powder 19 a, at least in a stable form, so that, after pressure relief, z. B. after lifting the press die 23 a , 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 pressure-resistant material, for example stainless steel or cemented carbide, 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 the pressing tool 9 has been withdrawn in the arrangement according to FIG. 1, a disk of silicon and diamond crystals in contact with the silicon is arranged within the pressed-in cavity 11 while filling the remaining cavity. Additional pressure-transmitting powder is then arranged above the cavity filled with silicon and diamond crystals, whereby the cell 10 shown in FIG. 2 and surrounded by powder is formed.

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 system. From Fig. 2 it can be seen that the cell 10 located within the cylindrical core of a mold 20 is surrounded by a mass 9 of pressure-transmitting powder medium. 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, ie compressed, with respect to their dimensions, so that a system is created which forms the cell enclosed by the powder contains, in which the resulting diamond crystal layer consists of more than 65 vol .-% diamond. The press mold 20 (ring 22 and press ram 23, 23 a ) can consist of tool steel, the ring 22 optionally being provided with a cemented carbide bushing 22 a in order to apply pressures of up to 14,000 bar to the cold press shown in FIG. 2 enable. Pressures above 14,000 bar have no noticeable advantage. Within the area enclosed by the press ram 23 , the sleeve 22 a and the press ram 23 a, pressure is preferably exerted in the range from 1400 to 7000 bar and usually up to 3500 bar to the pressure-transmitting medium by the press ram during cold pressing according to FIG. 2.

With cold pressing, the size of the cavities is between the crystals reduced, so that it for optimal training capillary-like pores in the diamond mass. Furthermore, the diamond crystal mass on the required diamond content of over 65 vol .-% brought.

After the cold pressing, the diamond content is the total pressed diamond crystal mass in the cell over 65 vol .-%. Often the diamond content of the compressed Diamond crystal mass in the range from 66 to less than 85% by volume be. The higher the diamond content of the compressed Crystal mass, the lower the proportion of between the crystals passing silicon, so that a accordingly harder diamond body is created.

The 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 rams 23 or 23 a is withdrawn and the 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 22 a , and enclosed within the cavity 31 between the graphite dies 32 and 32 a . To display the temperature of the dimensionally stabilized 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, thereby also causing evacuation of the system 21 including the cell 10 so that the system 21 and the cell 10 are substantially under a vacuum in which the hot pressing can be carried out. Nitrogen or hydrogen, or an inert gas such as argon, is passed into the furnace chamber to expose the system 21 in the furnace chamber, including the contents of the cell 10, to an atmosphere suitable for hot pressing. While with the help of the graphite stamp 32 and 32 a an axially acting hot press pressure is exerted on the system 21 , the temperature of the system is increased to the hot press temperature at which the silicon 12 in the form of a disk becomes liquid.

When hot pressing, the hot pressing temperature should be as possible can be reached quickly. The hot press temperature will under the hot pressing pressure usually at least one minute maintained long enough to provide adequate soak to ensure the diamond crystal mass. A hot one pressing time of 1 to 5 minutes is sufficient. Since the Conversion of diamond into non-diamond shaped elemental carbon largely from time and tem temperature depends and especially the probability the transformation into non-diamond shaped elemental coals the higher the temperature and the higher the temperature It is time to maintain the temperature Hot pressing must be done before 5 vol .-% diamond converted to non-diamond shaped elemental carbon are. The extent of the conversion can be determined empirically will. When converting 5 or more vol .-% diamond in non-diamond shaped elemental carbon optionally a non-diamond phase in the end product shaped elemental carbon that remains unfavorable to the mechanical properties of the end product could impact.

It is particularly important that substantially isostatic conditions are maintained during hot pressing, so that when the silicon becomes liquid, the liquid silicon does not escape between the diamond mass 13 and the cavity 11 and can escape to a significant extent, but rather is forced into the diamond crystal mass 13 . The portion of the pressure-carrying powder that is closely related to the contents of the cavity, ie, the portion of the powder that preferably extends outwardly from the interior wall of the cavity or from the cell to approximately 25 mm, should not be related Have pores larger than 5 µm in size to prevent excessive leakage of liquid silicon during hot pressing.

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 sufficient to maintain its dimensional stability acts on the cell 10 in the system 21 during cooling. 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 produced according to the invention body contains diamond crystals that are firmly attached to each other are linked to a binder that consists essentially of Silicon carbide and elemental silicon. The Diamond crystals have a size of 1 to 1000 µm. The diamond content of the polycrystalline body ranges from 65 to less than 80% by volume and is often about 78% by volume. The polycrystalline diamond body contains up to 35% by volume Silicon, which is essentially uniform in the polycrystalline Diamond body is distributed. The one in contact with the Surface of the diamond crystals standing part of the bandage means consists of a substantial amount of silicon carbide, d. that is, at least 85 and preferably 100% by volume of the in direct contact with the surfaces of the diamond crystals Standing part of the binder is silicon carbide. The  polycrystalline diamond body is non-porous or at least at least essentially non-porous.

The proportion of silicon carbide in the binder of the poly crystalline body can vary depending on the extent of the reaction the surfaces of the diamond crystals and the penetrating silicon as well as between non-diamond shaped elemental carbon and penetrating silicon more or less fluctuate. You go assuming that all other factors are the same, then it depends on Amount of silicon carbide present mainly from the applied hot pressing temperature and the duration, within which the applied hot pressing temperature is maintained has been. The silicon carbide content of the binder increases with it increasing hot pressing temperature and / or duration. One can therefore, for example, empirically determine the process conditions, which must be followed to make a polycrystalline diamond to achieve bodies with a certain silicon carbide content. The The composition of the binder can vary widely fluctuate, 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 may be present. With detectable Quantity is the quantity that means one electron Microscope when radiating a thin part of the diamond body due to the occurrence of electron beam diffraction can be. In general, however, the binder consists in white Substantially from silicon carbide in an amount of 2 to 30 vol .-%, based on the volume of the polycrystalline Diamond body, and made of elemental silicon in one Quantity from 33 to 5 vol .-%, based on the volume of the polycrystalline diamond body. The diamond content of the polycrystalline diamond body lies in an area which was from 65% by volume to approximately below 80% by volume to the volume of the diamond body.  

The polycrystalline diamond body is pore-free or at least substantially non-porous, d. that is, he can Voids or pores of less than 1% by volume on the volume of the body, provided the pores or cavities small (less than 0.5 µm) and sufficient are evenly distributed in the body so that they are none noticeable adverse effect on the mechanical Have properties of the body. The cavity or pore content of the polycrystalline diamond body can by conventional metallographic processes be determined. for example optically through Observation of a polished section of the body.

The polycrystalline diamond body is also free of ele mental, non-diamond shaped carbon, d. that is, he ent does not hold evidence from X-ray diffraction analysis bare amount of elemental, non-diamond shaped carbon.

In the method according to the invention, silicon and the diamond crystals in the form of layers arranged one above the other, the diamond body formed has at least one flat surface and can have a number of shapes, such as the shape a disc, a square, a rectangle, a rod or of a block.

When performing the method according to the invention Silicon used in the form of a tube or hollow cylinder, the The interior is packed with diamond particles, penetrates when hot press the liquid silicon into the compressed slide core crystals existing, creating a diamond body in The shape of a cylinder with a circular cross section is created.

If the silicon in the form of a Inserted rod, which is arranged in the middle of the cavity  and wherein the space between the rod and the mold cavity room wall is filled with diamond crystals, then penetrates during hot pressing the liquid silicon into the silicon rod enclosing diamond crystal mass, so that a diamond body in the form of a hollow cylinder.

A particular advantage of the invention is therefore that poly crystalline diamond bodies with different dimensions and Shapes can be made. For example, the diamond bodies have a width or length of 25 mm or more. Polycrystalline diamond body that has a lane of 25 mm or more possess and have a corresponding diamond content, can practically not be produced by processes for those in the diamond-stable area of the state diagram of carbon pressure and temperature conditions come into use because of the generation and maintenance maintenance of such high pressure and temperature conditions necessary equipment an extraordinary require complex construction and therefore only one have limited capacity. On the other hand, too polycrystalline diamond body by the process of Invention extremely thin down to one Layer thickness of only one diamond crystal layer be put.

A polycrystalline manufactured according to the invention Diamond body can be done by soft soldering, brazing or in otherwise on a suitable surface for example made of sintered silicon carbide, sintered Silicon nitride, cemented carbide or a metal such as Molybdenum, attached to form a tool insert will. The tool insert thus formed can be used for ver Use as a cutting tool in a machine tool be mounted on a suitable tool shaft. However, a polycrystalline diamond body can also be found on a tool holder mechanically clamped and as Cutting tool can be used.  

The invention is further illustrated by an embodiment explained.

Embodiment

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

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

The cylinder used as a press tool consisted 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 approximates the center axis of the die coincided.

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 powder-enclosed cylinder was then pressed together at room temperature with a pressure P 1 of 3500 bar. The press ram 23 a was then withdrawn, and with the press ram 23 the compact formed with the cylinder enclosed by the powder was partially pushed out of the die. The exposed part of the compact 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 with the same diameter as the inside diameter of the The mold cavity was placed on the bottom of the mold cavity. About 250 mg of diamond powder was placed on the silicon wafer  packed with graded grain size. The grain size of the Diamond powder ranged from 1 to 60 µm, approximately 40% by weight of the diamond powder has a grain size of below Had 10 µm.

One by hot pressing hexagonal boron nitride manufactured disc with the same diameter as the inside diameter of the mold cavity became within of the mold cavity on the diamond powder to ensure a polycrystalline diamond body with a flat surface.

The compact was then pushed through the die 23 a in the middle of the die, 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 available charge of the steel die was pressed at room temperature, ie cold, with a pressure P 2 of 5600 bar in the manner shown in FIG. 2, the contents of the mold cavity being essentially isostatic, ie one of all Side pressure was applied evenly. The pressing pressure was maintained until it had stabilized to form a dimensionally stable powder molding. It was known from previous experiments that the compressed diamond crystal mass in the powder molding formed had a diamond content of over 75% by volume and that silicon was present in an amount of about 40% by volume, based on the compressed diamond crystal mass.

The powder molding 21 formed 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 13.3 m bar and then filled with dry nitrogen. A pressure P 3 of approximately 350 bar was then exerted on the powder body in the graphite mold and maintained. 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 bar due to the thermal expansion of the entire system.

At 1500 ° C the pressure dropped to about 350 bar. This pressure drop indicates that silicon melted and liquid and into the diamond mass had penetrated. The pressure was increased again to 700 bar and maintain this value at 1500 ° C for one minute hold to a full soak in the diamond ensure crystal mass with silicon. The heating system was then turned off, but no additional Pressure was exerted. This made for a high pressure at high temperature and for a reduced pressure low temperature and thus for a sufficient geo metric stability ensured. The polycrystalline formed Diamond body was removed at room temperature.

After removing the scaly surface of the polycrystalline diamond body adhering hexagonal The diamond body had the shape of a boron nitride powder Disc with a diameter of about 9 mm and a thickness of about 1.25 mm.  

The polycrystalline diamond disc had essentially smooth flat surfaces and seemed from the binder to be well enforced. A visual check the diamond disc at 100x magnification below the Microscope revealed that the polycrystalline diamond disc was pore-free.

With the help of hammer and chisel, the disc was cut in two Halves broken apart. An examination of the break points the disc showed that the fracture surface across the Crystals and not along the crystal faces. This suggests that through the binder caused binding is very good and as firm as that Diamond crystals themselves. The fracture surfaces were non-porous 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.

The diamond content of the disc was approximately 72% by volume, based on the volume of the disc. The diamond content was standardized according to the Score method found using a micrograph with 690x magnification of the polished cross-section area was used and the analyzed surfaces area one for the microstructure of the whole body representative size.

An X-ray diffraction analysis of the broken one Body revealed that the body was made of diamond, silicon carbide and elemental silicon and the proportion of Silicon carbide and elemental silicon at least 2% by volume of the body. In X-ray diffraction analysis of the broken body, however, none of the elemental, non-diamond-shaped carbon phase determined.

Claims (5)

1. A method for producing a polycrystalline diamond body in which diamond crystals are arranged together with silicon in a cavity, the content of the cavity is exposed to pressure and temperature conditions at which the silicon melts and the pressure is switched off only after the cavity content has cooled, characterized that a cavity in which a diamond crystal mass and these adjacent a silicon is disposed mass, the cavity and its contents covered with additional powder mass and the space enclosed by powder mass cavity is pressed to form a dimensionally stable isostatic system is pressed into a form suitable for isostatic pressure transfer powder mass, in which over 65% of the volume occupied by the diamond crystal mass consists of diamond, while the silicon mass is present in an amount sufficient to fill the voids in the diamond crystal mass, the isostatic system in an inert atmosphere Is subjected to hot pressing for 1 to 5 minutes, which is carried out at a temperature ranging from the temperature at which silicon becomes liquid up to 1600 ° C. using a pressure in the range from 35 to 1400 bar, and during cooling one to Maintaining the system dimensions sufficient pressure is maintained. 2. The method according to claim 1, characterized in that for the diamond crystal mass diamond crystals with a used in the range of 1 to 60 µm graded size will. 3. The method according to claim 1 or 2, characterized in that the silicon mass is arranged in the form of a layer, over which the diamond crystal mass also in shape a layer is arranged. 4. The method according to claim 1 or 2, characterized in that the silicon mass in the form of a rod in the middle of the Arranged cavity and the diamond crystal mass in the Clearance between the silicon rod and the cavity wall is introduced. 5. The method according to claim 1 or 2, characterized in that the silicon mass arranged in the form of a hollow cylinder and the interior enclosed by the hollow cylinder with the Diamond crystal mass is filled.