PROCESS FOR MAKING DIAMOND AND CUBIC BORON NITRIDE COMPACTS

Abstract: The improved process for making diamond and cubic boron nitride compacts comprises embedding within the mass of abrasive crystals (18) at least one partition strip (20) subdividing the abrasive crystal mass (18), which partition strip (20) is characterized by maintaining segregation be­ tween the separate portions of the abrasive crystal mass during step A and being sufficiently pliable no to resist the compaction of the abrasive crystal masses; subjecting a mass of abrasive crystals (18) selected from the group consisting of diamond, cubic boron nitride and mixtures thereof, which mass is in contact with a source of catalyst/­ solvent for recrystallization of the abrasive crystals, to conditions of temperature, pressures and time which result in a compact having intercrystal bonding between adjacent crystal grains; recovering the compact produced; and re­ moving substantially all of the metallic phase from the compact of step B.

Description: Improved process for making diamond and cubic boron nitride compacts This invention is related to the high pressure/high temperature (HP/HT) process for making cubic boron nitride and diamond compacts. MDre particularly, it is related to a modification of the HP/HT process which can result in increased efficiency in the production of small compacts and in new types of compacts with improved characteristics. A compact is a polycrystalline mass of abrasive particles (e.g. diamond and cubic boron nitride) bonded together to form an integral, tough, coherent, high-strength mass. A composite compact is a compact bonded to a substrate material, such as a cemented, metal carbide (e.g. cobalt cemented tungsten carbide). The metal bonded carbide mass is generally selected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide and mixtures thereof with metal bonding material therein normally being present in a quantity from about 6 to 25 weight percent and selected from the group consisting of cobalt, nickel, iron and mixtures thereof. Compacts or composite compacts may be used as blanks for cutting tools, drill bits, dressing tools, and wear parts. Compacts made in a cylindrical configuration have been used to make wire drawing dies (see U.S. Patents 3,831,428 ; 4,129,052 ; and 4,144,739). One method for manufacturing compacts involves the steps of A. placing within a protective shield metal enclosure which is disposed within the reaction cell of a high pressure/high temperature apparatus (1) a mass of abrasive crystals (either diarrond or cubic boron nitride (CNB)) ; and (2) a mass of catalyst metal in contact with the mass of abrasive crystals ; and B. subjecting the contents of the cell to conditions of temperature, pressure and time sufficient to give intercrystal bonding between adjacent crystal grains. For example, the mass of catalyst metal could be in the form of a disc of one of the weIl known catalysts for diamond or CBN crystallization. Under the conditions, a compaction front advances through the dense diamond or CBN material, and the catalyst metal (in liquid form) makes itself available as a catalyst or solvent for recrystallizstion or intercrystailine bonding oi the diamond or CBN grains This process is sometimes known as the sweep-through method, i.e, the catalyst sweeps through the diamond or CB masa, The relative shapes of the abrasive mass and catalyst can be varied For example, the mass of diamond or CBN can be cylindrical, and the catalyst can be an annular shape surrounding the cylinder of abrasive crystals. The soured of catalyst may also be cemented metal carbide or carbide molding powder wherein the cementing agent is a catalyst or solvent for diamond or cBN recrystarnzation or growth. The catalyst is generally selected from cobalt, nickel and iron or aluminum alloy in the case of CBN. The catalyst may be mixed with the abrasive crystals in addition to or instead of being a separate mass adjacent to the abraseve crystals Also, in place of abrasive grains such as diamond or CBN, one may choose to utilize as raw materials other sources of carbon or boron nitride su"h as graphite, hexagonal boron nitride or wurtzite boron nitride which would be converted to diamond or cBN respectively during the HP/HT process. Procasses for such conversions are described in the patent literature, for example, U. S. Patent 3,407,445 and 3,850,053 (for diamond) and British Patent 1,317,716, U. S. Patents 3,212,852 and 4,18a494 and U. S. Serial Number 47,656 filed June 11, 1979 (for CBN), all of which are hereby incorporated by reference. High temperature and high pressure in the diamond or cBN stable region are then applied for a time sufficient to bond the abrasive crystals together. The resulting compact is characterized particularly by diamond-to-diamond or CBN-to- cBN bonding, i.e., intercrystal bonding between adjacent grains whereby there are parts of the crystal lattice which are shared between neighboring crlrsta2s (resulting from recrystallization at HP/HT conditions). Methods for making diamond compacts are detailed in U. S. Patents 3,141,746; 3,745,623; 3,609,818; and 3,850,591; and process for CB compacts are disclosed in U. S. Patents 3,233,988; 3,?43,489; 3,767,371; and 4,188,194 (all of which are incorporated herein by reference). The manufactire of thermally stable compacts is described in U. S. Patent 4,224,380. This patent teaches the removal of substantially all of the metallic (catalyst) phase from compacts to yield a compact consisting essentially of self- bonded abrasive particles with an interconnected network of pores dispersed throughout. Such compacts can withstand exposure to temperatures of about 1200 C to 13000C without substantial thermal degradation, an advantage over the compacts of, for example, U. S. Patent 3,745,623 which are thermally degraded at a temperature between 700 0C and 8000C. The metallic phase is removed by acid treatment, liquid zinc extraction, electrolytic depletion, or similar process The compacts of this type will be referred to throughout as thermally stable compacts. The current manufacturing methods of thermally stable compacts require a post pressing step, such as laser cutting, grinding, or lapping, for shaping each piece to the desired configuration, (eg. triangular or segment of a circle). This consumes time, labor and materials. Since diamond is the hardest known material and CBN the second hardest, the polycrystalline mass is most difficult to shape. The shaping step, whether by laser cutting, dicing with a diamond wheel, or other method, requires labor intensive handling for each final piece. This adds to the cost, logistics and time required to manufacture the product. The crushing or milling of large polycrystine pieces is not a viable method because the shape cannot be controRed and only a small percentage of the desired particle size is obtained. The problem is, therefore, to eliminate the individual handing requirements tor each piece while maintaining the desired shape of the pieces U. S Patent 3,949,062 describes one method for producing diamond compacts of a predetermined shape by surrounding a monolithic piece of graphite of a predetermined shape with catalyst and transforming it into polycrystaline diamond through a high pressur temperature process using a pulse of electric current. U. & Patent 3,785,093 proposes making sintered diamond and cermet mixtures by exposing such mites to conditions within the graphite (non-diamond) stable region while contained within graphite shells which are in turn contained within shells made of low melting metals (e.g.zinc). The diamond stable region is the range of pressure temperature conditions under which diamond is thermodynamically stable. On a preesuretemperature phase diagram, it is the high pressure side, above the equilibrium line between diamond and graphite. The cubic boron nitride stable region is the range af pressure temperature conditions under which cubic boron nitride is thermodynamically stable, On a presswetemperature phase diagram, it is the high pressure side, above the equilibrium line between cubic boron nitride and hexagonal boron nitride lathe case of normal (i.e. non-thermally stahle) diamond or CBN compacts, there is another problem connected with their use, not the manufacturing finishing steps. Diamond and CBN compacts, such as those manufactured by the catalyst sweep tlrougtr method, are very strong but very brittle materials Once started, fractures can propagate through the diamond or CBN mass. The chips fonned can be quite large and can limit the usefulness of the material. This is particularly true in the case of petroleum or rock drill bits where massive failure of the diamond layer of a composite compact can also lead to damage of the remaining cutten on the bit A technique is needed which would reduce the massive failure caused by fractures propagating through a well bonded polycrystailine brittle material such as the diamond layer af compact cutters used in petroleum drill bits U. S. Patent 4,255,165 describes a modification of composite compacts in which at least two cemented metal carbide masses are bonded to and interleaved with at least two masses af poiycrystalline diamond or CBN. This modification is said to provide internal reinforcement of the composite compact against massive fracture by enhancing resistance to crack propagation, U. S. Patents 4,063,909 and 4,108,614, as well as South African Patent Application T7/5521 disclose interposing a transition metal layer between the diamond particles and metal carbide af various types of composite compacts during manufacture. British patent 1,568,202 discloses laminated compacts in which bonding between adjacent diamond layers takes place through a metal or alloy layer. The difficulties discussed above can, to a great extent, be alleviated by embedding within the mass of abrasive crystals, before ElP/= sintering, at least one partition strip of a deformable material (e.g., metal or metal alloy) which extends through the shortest dimension of the abrasive crystal mass or layer. The strips may be oriented so as to segment or subdivide the abrasive crystal mass. In the cylindrical high pressure apparatus often used to make compacts, the strips are oriented longitudinaily or parallel to its axis. The partition strips should be deform able or pliable so that there is no bridging action or resistance by the partitions to the compression of the abrasive crystal mass. The abrasive crystal mass lose some of its volume (about 3096) during the compression of the ElP/HT process, which loss must be accommodated. The partition strips should also be stong enough to maintain segregation between the portions of the subdivided abrasive crystal mass. The partition strips may be in any convenient form, such as: flat strips, wire mesh, expanded metal, tubes, or closed shapes fabricated from flat metal pieces (eg. triangle or star shape). The closed shapes describe discrete volumes within the abrasive crystal my The partition strips can be any catalyst or inert pliable material which does not interfere with the sintering sweep through mechanism and which can be easily removed by post pressing operations. The partition strips are placed in the typical shield metal cup of the normal compact manufacturing process The cup is then filled with diamond or cBN and, in the ease of composite compacts, covered with a cemented metal carbide piece or carbide molding powder. The uniqueness Of this invention is based on the following discoveries: 1. When metal pieces which describe closed shapes (eg. tubes in the shape of circles, triangles rectangles, squares or stars) are used, the compact formed within the closed shape is maintained as a circle, triangle, rectangle, square or star after compression even though the diamond or CBN was in a molten metal envelope during the HP/HT process. 2. Group Viri metals of the first trrsition series, which are readily available, can be used as the deformable metal strip or partition material between the CBN or diamond messes. When the reaction volume is compressed to HP conditions and then heated to sweep through temperature, the pore volume in the diamond or CaN is filled with molten catalyst metal, and the metal strip or partition remains in position Of course, there is diffusion and alloying with the partition metal but the minimum volume wm have already been obtained through the packing down and compression of the abrasive crystals, and separation of the compacted shapes or crystal masses is maintained. 3. The melting points at the materials within the reaction volume appear to be the controlling parameters when catalyst assisted sintering occurs. When the partition or metal strip material is not a catalyst or solvent, it must have a melting point, under conditions present in the reaction zone of the HP/BT cell, at least slightly higher (eg. 200 C higher) than the catalyst melting point. This is to prevent the partition strip from melting and becoming mobile before catalyst sweep through occurs. In that event, the catalyst would be blocked by the partition strip material which would have swept through the diamond or CBN ahead of the catalyst. When catalyst solvent materials are used for the partitions, that is not a great concern. It must be recognized that although the melting point of a material may be below the catalyst melting point at atmospheric pressure, it can be different at greatly elevated press and in the presence of diamond or graphite. For example, nickel melts below the melting point of cobalt normally, but at HP/HT conditions in the presence of diamond, nickel melts or forms a eutectic at about 13940 C while the corresponding cobalt diamond eutectic occurs at about 1317oC. See Strong, L M. and Tuft, B. E*, Uhe Cobalt-Carbon System at 56 Kilobars,' General Electric Company Technical Information Series, July, 1974; and Strong, IL M. and Hanneman, R E, "Crystallization of Diamond and Graphite, The Journal of Chemical Pussies, Vcd. 46, pp. 3668-367S, (May, 1967). 4. The partition or metal strip material should be pliable or deformable in order to allow for diamond or CBN crystal compaction and the transmission of pressure more efficiently. When stiff preformed cemented carbide was used as a barrier or metal strip, efficient sintering was difficult because the relatively incompressible carbide walls hindered pressure transmission to the abrasive crystals. This improved process permits the pressing of diamond or CBN compacts to the desired shape with little or no finishing steps required. A compact is removed from the high pressure apparatus, and the shield metal sleeve and any adhering metal from the shield metal cup or disc are removed in the usual manner (eg., peeling off, grinding or lapping). At this point, the compacts comprise polycrystalline diamond or CBN having embedded therein one or more pieces of material in basically the same shape as the partition strips which were placed into the reaction volume of the high pressure cell. Where thermally stable compacts are desired, the compacts recovered from the cell are further treated by the process of U. S. Patent 4,224,380. For example, they could be contacted first with a hot medium comprising nitric acid and hydrofluoric acid and secondly with a hot medium comprising hydrochloric acid and nitric acid (see example rn Of U. S. P. 4,224,380). By exposing the compacts to this bulk acid treatment, the embedded partition strips are removed and the compact discs are separated into smaller compacts of the various shapes described by the partition strips (eg., cylinders, triangles, semi-circles, etc.). Besides having these pre determined shapes; the smaller compacts are thermally stable as a result of the bulk acid treatment. Mechanical removal of the partition strips is also possible by grit blasting, for example. However, the acid treatment is preferred because it is simple and is the same technique used to remove the infiltrated catalyst (e.g., cobalt) in the polycrystailine mass in order to obtain thermally stable compact This invention provides an efficient and practical method for the manufacture of thermally stable compacts There are no shaping or cutting operations needed. Only the metal removal step by bulk acid treatment is required Individual handling is virtually eliminated. This process improvement allows many pieces to be nested together in one high pressure cell and treated as a group during EP/= operations. This is generally a less expansive and more convenient method of obtaining compacts in the desired shape than the conventional methods (eg. laser and electrical discharge machining). In fact, it is referred to as "press to shape. In the case where one does not perform the bulk acid treatment, the embedded partition strips (placed in non-working areas within the sintered mass) remain and serve as chip arresters which limit the movement of fractures within the polycrystalline diamond or CBN. The configuration of the strips will depend upon the maximum size chip allowable. The compact blanks are shaped as usual. FIG. 1 is an elevation view in section of an HP/HT reaction cell as modified by the improvement of the invention. FIG. 2 is a perspective view of one of the shield metal cups from the cell in FIG. 1. FIG. 3 is a plan view section taken through the reaction cell where indicated, FIG. 4 is a plan view similar to FIG. 3, except that the partition strips are circular tubes instead of triangular tubes. FIG. 5 depicts a composite compact in perspective, showing the chip arresters which are part of the invention. The feasibility of placing partitions within the siutered diamond mass was first tested in the cobalt sweep through process by embedding molybdenum, Monel nickel copper alloy (Monel is a trademark of International Nickel Co.) and stai}iess steel wire mesh into the diamond powder in a composite compact tool blank cdL The results confirmed the possibility of the partition strip method. Molibdenum and the Manel nickel copper alloy exhibited acceptable results, but stainless steel had delamination and chippage problems. The latter situation was the result of the steel reacting with the protecting shield metal cup and allowing the salt to penetrate and contaminate the diamond. Tantalum and titanium tubes (0.200 inch or 5.08mm outside diameter) were cut into 3.81 mm length, placed in the normal zirconium shield metal cups, filled with diamond powder (about 6-8 microns largest dimension) covered with cobalt catalyst dises and loaded in a HP/HT reaction cell Using this method with tubes of different shapes, cylindrical, triangular, and star shaped pieces were obtained. After those runs, nickel, iron and zirconium tubes with L6mm internal diameter were cut to length, loaded with diamond in typical HP/HT cells and pressed. The nickel tubing appears to be very compatible with the cobalt catalyst sweep through method. Zirconium is acceptable but more expensive. Ultimate compression tests of leached samples from the iron and nickel partition runs were made, and the results are 8.30 x 105 psi (5.72 x 106 kilopascals (kPa)) for the nickel partition and 7.40 x i05 psi (5.10 x 106 kPa) for the iron partition pieces. Both numbers are an average of ten tests and had values to 106psi ( & 9 x 106 kPa). Thus, the preferred partition materials, when using cobalt catalyst sweep through are iron and nickel, nickel being the most preferred The materials which can be used are those from Groups m B, IV B, V B, VI B, VIE B, and VIII of the periodic table and their alloys. Stainless steel is also acceptable if isolated from the shield metal cup. Although it is feasible to use cobalt itself or lower melting catalyst solvent (erg. Invar iron-nickel alloy) materials as partitions, they are not preferred. In the case at closed shape partitions, the use at smoothwsided (e. g. continuous drawn) tubes may give more pieces per cell with the thinner tube walls. A further aspect at this invention is the bonding together at several partitions describing closed shapes into a bundle. Sections can be severed from the bundle, which sections resemble a honeycomb. These honeycomb partition bundles represent an efficient means at packing the maximum number at partition strips for discrete small compacts into a given cell volume. Such bundles may be made by diffusion bonding individual closed shapes together. Diffusion bonding is a method for attaching two or more metal shapes by thermally cycling the pieces which are in contact with each other to a temperature high enough to allow the metal to bond by solid state diffusion but not high enough to distort the shapes of the pieces. The materials are never brought to their melting point nor are they held at temperature long enough to promote volume or shape chcmges. The result is an integral unit composed at a plurality of the starting shapes This unit can be cut to the desired thickness and used as a partition. This eliminates the need af individually handling the many small partitions when loading a high pressure cell. For example, a multiplicity of nickel (melting point 1453 C) tubes can be bonded into a structural unit by heating in a vacuum to 12000C for ten minutes. A quantity of clean nickel tubes (placed inside a hollow graphite rod in a vacuum furnace) is heated to 1200 C under vacuum. A carbon coating is deposited on the tubes by introducing methane unto the furnace (allowing vacuum to drop to about 28 in. Rg. gauge pressure) and aIlpwing it to remain for about five minutes. Full vacuum and 12000 C conditions are resumed, followed by a second introduction at methane, after which the furnace is allowed to cool and the tube bundle is removed. The severing at sections from the tube bundle is conveniently done by wire electrical discharge machining (EDM). The carbon coating on the tubes helps to prevent distortion at very thin wall tubing during the wire EDM cutting. In the case of tubes having a wall thickness substantially greater than two milts, the carbon coating is not required to prevent distortion. One preferred form at a HP/HT apparatus in which the compacts of this invention may be prepared is the subject at U. S. Patent No. 2,941,248 (incorporated herein by reference) which is called a belt apparatus. It includes a pair of opposed cemented tungsten carbide punches and an intermediate belt or die member of of the same mater The die member includes an aperture in winch there is positioned a reaction vessel shaped to contain a charge assembly. Between each punch and the die there is a gesket assembly comprising a pair of thermally Insulating and electically nonconducting pyrophyllite members and an intermediate metallic gasket. The reaction vessel, in one preferred form, includes a hollow salt cylinder The cylinder may be of another material, such as talc, which (1) is not converted during HP/HT operation to a stronger, stiffer state (as by phase transformation and/or compaction) and (b) is substantially free of volume discontinuities occurring under the application of high temperatures and pressures, as occurs, for example with pyrophyllite and porous alumina. Materials meeting the other criteria, set forth in U.S. Patent No. 3,630,652 (Col. 1,159-Col. 1,12, incorporated herein by reference) are useful for preparing the cylinder. Positioned concentrically within and adjacent to the cylinder is a grphite electrical resistance heater tube. Within the graphite heater tube, there is concentrically positioned a cylindrical salt liner. The ends of the liner are fitted with salt plugs disposed at the top and the bottom. Electrically conductive metal end discs are utilized at esch end of the cylinder to provide electrical connection to the graphite heater tube. Adjacent to each disc is an end cap assembly each of which comprises a pyrophylite plug or disc surrounded by an electrically conducting ring. Operational techniques for simultaneously applying both high pressure and high temperature in this type of apparatus are well known to those skilled in the super-pressure art. Refering to Fig. 1, the charge (or reaction zone) assembly 10 its within the space defined by the seit liner and the salt plugs. The assembly consists of a a. cylindrical sleeve 11 and end caps 12 oi shield metal selected from the group consisting of zirconium, titanium, tantalum, tungsten and molybdenum. Within the shield metal sleeve are one or more sub-assemblies each defined by a shield metal dise 16 and a shield metal cup 14. A mass of abrasive crystals 18 (diamond, CBN or mixtures thereof) is disposed within the cavity defined by the cup and the disc This mass may also contain graphite and/or a metal catalyst A disc of catalyst solvent (eg. cobalt) 22 is shown on top of the abrasive crystal mass, just underneath the shield metal disc. The number of sub-assemblies within the reaction zone can be varied and is not critical. In Fig. 1, five sub assemblies are shown and each one is separated by a separator disc 24 made of an inert material such as dehydrated mica. It composite compacts are desired, a mass of sintered metal bonded carbide (e. g. titanium, tungsten, or tantalum carbide) or carbide powder with appropriate metal bonding medium (e. g. cobalt, iron or nickel) would also be placed within the sub-assemblies. In Fig. 1 this would appear as a disc or layer either on top of or underneath the abrasive crystal mass 18. The manufacture of composite compacts is well know, and more details may be found in U. S. Patent 3,745,623. The partition strips of this invention are shown as elements 20 in the sub- assemblies. In the particular embodiment of Figs. 1-3, the partition strips are triangular shapes which have been diffusion bonded together into a honeycomb pattern as described above. Fig. 2 shows clearly how the honeycomb partitions are placed into the shield metal cup during cell assembly. Fig. 3 shows how the individual triangar masses of abrasive crystals 18 are seeeegated. The abrasive grains which are outside of the tubular partitions wfll be designated interstitial diamond or CBN 2 & BR< Fig. 4, of course, shows a variant of the partition shapes which utilizes four cylindrical tubes 21 rather than triangular shapes. Another possible variation is to effectively double the number of compacts made in a given sub-assembly by placing a refractory metal disc (e. g. zirconium) midway through the sub-ssembly. For example, such a zirconium disc would appear in a subeembly in Fig. I as a horizontal element dividing a given subassembly into top and bottom halves. Of course, the partition tubes would also be split in half. This technique will work if the catalyst solvent discs are placed one on either side of the zirconium disc or if the catalyst disc 22 remains where it is shown in Pig. 1. Any unused volume within the charge assembly may be taken up with a disc made of the same material as the salt cylinder (eg., sodium chloride) and discs made of hexagonal boron nitride to minimize the entry of undesirable substances into the sub-assembly defined by the shield metal disc and cup. Typical conditions for the HP/HT process are: (1) for diamond (a) a pressure of at least 50 kbars at a temperature of at least 13000C and within the diamond stable region; and (b) a reaction time of 3-120 minutes; (2) for cubic boron nitride (a) a pressure of at least 42 Roars at a temperature of at least 13000C and within the cubic boron nitride stable region; and (b) a reaction time of about 2-120 minutes. The charge assembly is loaded into the reaction vessel which is placed in the HP/HT belt apparatus. First, the pressure and then the temperature are increased and held at the desired conditions for sufficient time for sintering to occur. It is important that the apparatus be brought to operating temperature onty after operating pressure has been reached. If temperature is brought above the melting point of the catalyst before operating pressure has been reached, the sweep through would be commenced prematurely. The sample is then allowed to cool under pressure for a short period of time, and finally the pressure is decreased to atmospheric presure, and the compact is recovered. As stated in the background section, compacts may also be made using other carbon or boron nitride sources such as graphite, hexagonal boron nitride (HBN) or wurtzite boron nitride (WBN) as raw materials instead af diamond or CBN. When processed in accordance with the patents listed in the background section, these r1nr materials are converted into compacts The processes are HP/HT processes using apparatus similar to that described above. The operating conditions are typically: for graphite - 50-62 kilobars, 1200-1600 0C, for 30 seconds to 40 minutes time, in the presence of nickel or cobalt catalyst; for HBN - 50-150 kilobars, 1800-3000 C, for 1 to 30 minutes; and for WEN - suitable conditions are found in U. S. Patent 3,876,751 which is incorporated herein by reference (eg. 50 - 300 kbars, 1900 - 25000 C, for 1 to 7 minutes. The we of the partition strip improvement of this invention is also applicable when using these raw materials. One may use graphite or hexagonal boron nitride in the form of powder or pellets. It is also feasible to machine graphite or RBN rods to the shape which would fit within the space defined by the partition strip and the shield metal cup. There would be more volume change during the HP/HT process using these raw materials than there is either in the case of diamond or CBN, since there is an increase in density due to the phase change as well as the physical packing. This only serves to emphasize the importance of pliability in the partition strip material. As stated earlier, after removal of any adhering cell materials from the compacts resulting from the ES/HT process, the recovered compacts comprise the polycrystalline mass of abrasive grains bonded together having embedded within the mass the partition strips, basically in the same shape as they were placed into the sub-assembly. Thus, for the charge assembly of Figs. 1 - 3, the compacts at this point would resemble Fig. 3 without elements 11 and 14, the polycrystalline material and the partition strips being one integral mass. In order to make thermally stable compacts, this mass could be contacted first with a hot medium comprising nitric and hytofluoric acids and contacting it subsequently with a second hot medium comprising hydrochloric and nitric acids. Substantially all of the partition strip and catalyst solvent material infiltrated into the compact body would be removed by this process if it were carried out for a sufficient length of time in accordance with the teaching of U. S. Patent 4,224,380. The result would be 24 small triangular, thermally stable compacts per sub-assembly and 120 such compacts made per HP/HT run. Fig. 5 represents a composite compact made with a plurality of partition strips 28 arranged in a cross hatched pattern through the abrasive crystal layer. In applications such as rock drill bits, the size of chips knocked from the compact cutters would be limited by the embedded chip arresters (partition strips) to the shapes (e. g. small squares) described by the chip arrester configuration. Thus, for example, such a chip might be limited to a single piece 30 from the diamond layer ratherthanamassive portion af the whole layer Iron, nickel,and cobalt are the preferred metals for such chip arresters because they are relatively inexpensive, readily available, and do not form strong cartides like the refractory metals do. In the case of refractory metals, fractures may propagate mare easily and continue into the neighboring subsets of the polycrystailifle mass. If desired, any exposed partition strips at the face or edge of a compact may be removed by grit blasting or selective etching in order to produce multiple, free standing polycrystalline diamond or CBN zones on the tool blank. Another alternative would be to extend the chip arresters or partition strips into the cemented metal carbide substrate 32 of a composite compact during processing. This would effectively reduce chip propagation in the substrate. However, this technique may not work as effectively as the chip arrester concept in the diamond or cBN layer because metals such as nickel, cobalt and iron would probably diffuse into the metal carbide structure and, in the case of refractory metals, brittle carbides would probably be -oreed which would reduce their chip arresting properties.

Claims: CLAIMS I claim 1. In a process for preparing a compact which comprises A. subjecting a mass of abrasive crystals (18) selected from the group consisting of diamond, cubic boron nitride and mixtures thereof, which mass is in contact with a source of catalyst/ solvent for recrystallization of the abrasive crystals, to conditions of temperature, pressure and time which result in a compact having intercrystal bonding between adjacent crystal grains ; and B. recovering the compact produced ; and C. removing substantially all of the metallic phase from the compact of step B the improvement which comprises embedding within the mass of abrasive crystals (18) at least one partition strip (20) subdividing the abrasive crystal mass (18), which partition strip (20) is characterized by maintaining segregation between the separate portions of the abrasive crystal mass during step A and being sufficiently pliable not to resist the oompaction of the abrasive masses. 2. The improved process as recited in claim 1, wherein step C is accamplished by acid treatment. 3. The improved process as recited in claim 2 wherein the acid treatment comprises contacting the compact from step B first with a hot mixture of nitric and hydrofluoric acids and secondly with a hot mixture of hydrochloric and nitric acids. 4. The improved process as recited in claim 1 wherein the mass of abrasive crystals and the catalyst/solvent source have been placed within a protective shield metal enclosure (11, 12) which is disposed within the reaction zone (10) of a high pressure/high temperature apparatus for carrying out step A. 5. In a process for preparing a compact which comprises A. subjecting a mass of abrasive crystals (18) selected from the group consisting of diamond, cubic boron nitride and mixtures thereof, which mass is in contact with a source of catalyst/ solvent for recrystallization of the abrasive crystals, to conditions of temperature, pressure and time which result in a compact ; and B. recovering the compact produced the improvement which comprises embedding within the mass of abrasive crystals (18) at least two partition strips (20) extending through the shortest dimention of the abrasive crystal mass which partition strips (20) are characterized by maintaining segregation between the separate portions of the abrasive crystal mass during step A and being sufficiently pliable not to resist the compaction of the abrasive crystal mass. 6. The improved process as recited in claim 5 wherein the mass of abrasive crystals and the catalyst/solvent source have been placed within a protective shield metal enclosure (11, 12) which is disposed within the reaction zone (10) of a high pressure/high temperature apparatus. 7. The improved process as recited in claim 6 wherein the reaction zone (10) is cylindrical in shape, and the partition strips (20) are oriented parallel to the axis of the reaction zone. 8. The process as recited in claim 5 which further comprises removing the exposed parts of the partition strips (20) from the compacts recovered in step B in order to produce multiple, free standing polycrystalline abrasive crystal zones on the surface of the compact. 9. The process as recited in claim 5 which further comprises disposing the mass of abrasive crystals in step A in contact with a metal carbide. 10. The improved process of claim 9 wherein the metal carbide is selected from the group consisting of tantalum carbide, titanium carbide, and tungsten carbide. 11. The improved process of claim 9 wherein the partition strips are extended into the metal carbide. 12. The improved process as recited in claims 1 or 5 wherein the partition strip (20) is not a catalyst/solvent for the abrasive crystals and wherein its melting point, under the conditions of the HP/HT process, is at least slightly higher than that of the catalyst/solvent of step A. 13. The improved process as recited in claim 12 wherein the partition strips (20) are made of a material selected from the group consisting of a Group III B, IV B, V B, VI B, VII B, and VIII metals and their alloys. 14. The improved process as recited in claim 12 wherein the partition strips (20) are made of a material selected from the group consisting of irolybdenum, nickel-copper alloys, stainless steel, tantalum, titanium, iron, nickel and zirconium. 15. The improved process of claim 14 wherein the partition strip material is selected from the group consisting of nickel, iron and their alloys. 16. The improved process as recited in claims 1 or 5 wherein the partition strips (20) describe closed shapes. 17. The improved process as recited in claim 16 wherein the closed shaped are selected from the group consisting of circles, triangles, rectangles, squares, and star shapes. 18. The improved process as recited in claim 17 wherein the partition strips (20) comprise a plurality of shapes joined in a bundle. 19. An improved compact of a polycrystalline mass (18) comprising (a) polycrystalline abrasive grains selected from the group consisting of diamond, cubic boron nitride, and mixtures thereof ; and (b) a catalyst/solvent, said abrasive crystal grains, in random orientation, being directly bonded to adjacent crystal grains in said mass thereof by intercrystal bonding wherein the improvement comprises at least two partition strips (20), embedded within the polycrystalline mass and extending through its shortest dimension. 20. The improved compact of claim 19 wherein the partition strips (20) are made of a material selected from the group consisting of iron, nickel and cobalt. 21. The e improved compact of claim 20 from which the exposed partition strips (20) have been rertoved to produce multiple free standing polycrystalline abrasive zones on the face of the compact. 22. The improved compact as recited in claim 19 which is a composite compact of said polycrystalline mass of crystal grains adjacent and bonded to a cemented metal carbide mass. 23. The e improved composite compact of claim 22 in which the partition strips (20) extend into the cemented metal carbide mass. 24. In a process for preparing a compact which comprises A. subjecting a raw material selected from the group consisting of graphite, hexagonal boron nitride, and wurtzite boron nitride to conditions of pressure, temperature and time which result in a compact and B. recovering the compact produced the improvement which comprises embedding within the raw material at least one partition strip (20) characterized by maintaining segregation between the separated portions of the raw material during step A and being sufficiently pliable no to resist compaction of the raw material.

Inventors: GIGL, PAUL DONALD
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1982
Main classification: B01J3
IPC codes: C04B35, B22F7, B01J3, C22C1, E21B10