Abstract:
A method of making a bonded, coherent material comprising a mass of diamond crystals in a matrix, which optionally contains another phase. The method includes the steps of providing a source of diamond crystals, providing a plurality of diamond centers defined by diamond crystals, producing a reaction mass by bringing the source and growth centers into contact with a solvent/catalyst, subjecting the reaction mass to conditions of elevated temperature and pressure suitable for crystal growth in the reaction zone of a high temperature/high pressure apparatus to produce the material, and removing the material from the reaction zone. The method is characterized by providing the necessary supersaturation of carbon in the solvent/catalyst, at least in part and preferably predominantly, by a selection of particle size difference between the source crystal and the growth centers. The mass of diamond crystals in the matrix of the bonded, coherent material of the invention has a high concentration of twinned diamonds.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a diamond crystal containing material useful, for example, as a tool component or insert. 
     The manufacture of diamond matrix composites or tool materials or components, such as saw segments, grinding wheels and polycrystalline diamond (PCD) products, is well established. There are various methods used in their manufacture. For saw segments, pellets, pearls, and the like, diamond powder is mixed with matrix material and the mixture sintered, substantially at atmospheric pressure, to produce the component. Alternatively, the molten matrix material is infiltrated into a bed of the diamond powder, also substantially at atmospheric pressure, to produce the component. For PCD products, diamond powder is sintered under conditions of high temperature and high pressure in the presence of a solvent-catalyst, and the resultant piece shaped afterwards to produce the final component. 
     In essence, each method and product starts with diamond powder and then the component is fabricated. Some of these methods are conducted at substantially atmospheric pressure, and components produced by them, are restricted to matrices that sinter or infiltrate at relatively low temperature so that graphitisation of the diamond is avoided or minimised. 
     In the manufacture of PCD products, the solvent-catalyst is restricted usually to the matrices used for the production of the cemented tungsten carbide support, or in the case of the more thermally stable products, the infiltrant is restricted to those elements or compounds which react with the diamond to form a desirable phase, e.g. silicon forming silicon carbide. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a method of making a bonded, coherent material comprising a mass of diamond crystals in a matrix, optionally containing another phase, includes the steps of providing a source of diamond crystals, providing a plurality of growth centres defined by diamond crystals, the quantity of source crystals generally being greater than that of the growth centres, producing a reaction mass by bringing the source and growth centres into contact with a solvent/catalyst and the other phase, when used, subjecting the reaction mass to conditions of elevated temperature and pressure suitable for crystal growth in the reaction zone of a high temperature/high pressure apparatus to produce the material and removing the material from the reaction zone, the necessary supersaturation of carbon in the solvent/catalyst being achieved, at least in part, and preferably predominantly, by a selection of particle size difference between the source crystal and the growth centres. 
     The bonded, coherent material made by the method of the invention has been found to contain a mass of diamond crystals in which at least 40 percent, typically at least 80 percent, and generally substantially the entire mass, consists of synthetic twinned diamonds. The twinned diamond include contact twins, macle twins, including multiple and single macle twins, polysynthetic twins and star twins, i.e. a multiple twin in which at least some of the twin planes are not parallel. Various shapes of twin diamonds are also to be found. These shapes include blocky or cube shape, plate shape and column shape. For the plate and column shaped diamonds, the crystals have a high aspect ratio, i.e. a high ratio of longest dimension to shortest dimension. A bonded, coherent material of this type is believed to be new and forms another aspect of the invention. 
     The bonded, coherent material of the invention may, for example, be used as a tool component, blank or insert, bearing surface, substrate for further processing, abrasive material, heat sink, biomedical material, catalyst body or the like. These materials in their application all use the properties of diamond, the matrix or a combination of the properties of diamond and matrix. 
     The material may have zones of different properties. For example, the zones may vary in crystal concentration or size, in matrix, in nature of the other phase, or in a combination thereof. The differing zones may extend in layers or regions which are distributed in a random or ordered way, for example, from one side of the material to an opposite side or may extend in layers from a central point to an outside surface of the material. 
     The invention has particular application to materials which have a diamond content of less than 80 percent by volume. 
     The material may be produced in such manner as to provide it with a substrate to which it is bonded. The nature of the substrate may be chosen to complement the properties of the material. 
    
    
     BRIEF DESCRIPTION OF THE PHOTOGRAPHS 
     The photographs which form FIGS. 1 to  10  show examples of twinned diamond crystals present in a diamond crystal containing material made by the method of the invention. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     The invention allows for the manufacture of a tool component or material by preshaping a mass of source crystals, growth centres and matrix material and causing the growth centres to grow and the matrix to form in the same operation. This allows, for example, for the manufacture of a tool component or material to near net shape and dimension for end use. The nature of the matrix determines the service conditions which the tool component or material can endure. The supersaturation-time profile determines the growth rate and size of the diamond and the relative amounts of the crystal source growth centres and matrix in the preshaped mass determine the crystal concentration in the tool component or material. 
     The preshaping or preparation of the crystals and matrix can be done by any conventional method, e.g. hot pressing, cold compaction with and without a temporary binder, or slip casting. The chosen conditions for preshaping or preparation are preferably such that the diamond is not substantially graphitised. 
     In the method of the invention, the growth of crystals is achieved, at least in part, by supersaturation created by a difference in particle size between the source crystals and the growth centres. The source crystals and growth centres may be provided by particles at opposite ends of a particle size range. Thus, in this case, the growth centres will be provided by crystals at the higher end of the particle size range, whilst the source crystals will be provided by crystals at the lower end of the particle size range. The quantity of crystals, i.e. number of crystals, at the lower end of the range will generally be much greater than that at the higher end of the range. 
     The source crystals will be smaller than the growth centres. The size of the source crystals will thus depend on the size of the growth centres. It has been found that particularly good diamond growth and a particularly effective bonded, coherent material can be produced if the source crystals have a size of less than 20 microns, and generally less than 15 microns. 
     The growth centres may also be provided by seed crystals which are separate and distinct from the source crystals. Such seed crystals will generally be substantially larger than the source crystals. An example of this form of the invention is using particles of a size less than 10 microns as source crystal particles, and seed crystals having a size substantially greater than 10 microns, e.g. at least 40 microns, as growth centres. The quantity of seed crystals will generally be much greater than that of the source crystals. 
     Examples of suitable solvent/catalysts are transition metal such as iron, cobalt, nickel, manganese and alloys containing any one of these metals, stainless steels superalloys (e.g. cobalt, nickel and iron-based), bronzes including cobalt-containins bronzes and brazes such as nickel/phosphorus, nickel/chromium/phosphorus and nickel/palladium. Other suitable solvent/catalysts for diamond are elements, compounds and alloys not containing transition metals, e.g. copper, copper/aluminium and phosphorus, and non-metallic materials or a mixture thereof such as alkaline, alkaline earth metal hydroxides, carbonates and sulphates. 
     The source particles may be synthetic diamond, including polycrystalline diamond, produced by conventional high pressure/high temperature processes. The source particles may also be natural diamond (including carbonado), shock-wave diamond or CVD diamond, i.e. diamond produced by chemical vapour deposition. The growth centre diamonds may be of a similar type, except they will, of course, always be larger in size than the source diamonds. 
     The seed crystals may have well-developed facets and be devoid of twin planes, e.g. cubes, octahedra and cubo-octahedra, or they may contain twin planes, or they may be irregular, rounded or spheroidal. The seed crystals may be coated or clad, e.g. with solvent/catalyst. 
     The conditions of elevated temperature and pressure which are used in the method are known in the art. The synthesis conditions may be those under which diamond is thermodynamically stable. These conditions are well known in the art. Generally, the elevated temperature will be in the range 1200 to 1500° C. and the elevated pressure will be in the range 50 to 70 kilobars (5 to 7 GPa). These elevated temperature and pressure conditions will be maintained for a period sufficient to allow the crystal growth to occur. The time will generally be greater than 15 minutes and can be up to one hour or longer. 
     It is also possible to produce diamond growth under conditions which are outside the region of thermodynamic stability of diamond. Conditions of temperature and pressure outside the region of thermodynamic stability of diamond can be used if the Ostwald rule dominates the growth process rather than the Ostwald-Volmer rule (see Bohr, R Haubner and B Lux Diamond and Related Materials volume 4, pages 714-719, 1995)—“According to the Ostwald rule, if energy is withdrawn from a system with several energy states, the system will not reach the stable ground state directly, but instead will gradually pass through all intermediate states. In addition, according to the Ostwald-Volmer rule, the less dense phase is formed (nucleated) first. Where the two rules would appear to contradict each other, the Ostwald-Volmer rule has priority over the Ostwald rule.” In the case of diamond crystal growth outside its region of thermodynamic stability, the Ostwald-Volmer rule can be suppressed by, for example, the application of pressure, thus allowing the growth of diamond on pre-existing diamond particles provided graphite crystals are substantially absent. Although isothermal and isobaric conditions are not essential to the practice of this invention, such conditions are preferred as then the method can be more easily controlled. 
     The source crystals and the growth centre crystals are brought into contact with a suitable solvent/catalyst to create a reaction mass. Generally, the crystals will be mixed with the solvent/catalyst in particulate form. There must be sufficient source crystal to create supersaturation of carbon in the solvent/catalyst. Solution of the source crystal in the solvent/catalyst may be in solid or liquid state. The content of source and growth centre diamond, together in the reaction mass will generally be at least 10% by volume and generally less than 80% by volume. A typical content of source and growth centre diamond is 30% by volume. 
     The reaction mass may be placed in the reaction zone of a conventional high temperature/high pressure apparatus and the contents then subjected to the desired elevated conditions of temperature and pressure. The source material dissolves preferentially with respect to the coarser growth centre crystals in the catalyst/solvent. The carbon solute migrates to the growth centres and precipitates or grows thereon. The crystals which are produced will have a morphology which is dependent on the saturation-time profile utilised, apart from the temperature and pressure conditions and chemical composition of the solvent/catalyst which also influence morphology. 
     The matrix of the diamond crystal-containing material of the invention may contain another phase, or third phase. The other phase should be thermodynamically stable under the conditions of manufacture of the product and may be insoluble, or substantially insoluble, in the solvent/catalyst under these conditions. When the other phase material is soluble, or substantially soluble in the solvent/catalyst, it may be protected by a coating or cladding of lesser solubility. 
     The other phase and the nature thereof, will depend on the type of product to be produced. The other phase may take the form of particles, fibres, whiskers, platelets or the like. Examples of suitable third phase materials are carbides, oxides, sulphides, nitrides, silicides, borides, elemental materials or a mixture thereof or bonded materials such as cemented carbides. Specific examples of suitable third phase materials are tungsten carbide, cemented tungsten carbide particles, titanium carbide, aluminium oxide, titanium nitride, silicon nitride, silicon carbide, aluminium nitride, cubic boron nitride and the like. 
     The other phase may also be or contain a lubricant such as graphite, hexagonal boron nitride or molybdenum disulphide. With the inclusion of such lubricants in the material, the use of external lubricants may be avoided. 
     The other phase, when in particulate form, may have a particle size which is the same as, or differs from, that of the crystals of the material. 
     The other phase may contain more than one component, e.g. contain both a carbide and a nitride, or it may include a number of different phases. 
     The other phase will generally be mixed with the solvent/catalyst and the diamond source and growth centre material to produce a reaction mass. The reaction mass is then subjected to the elevated temperature and pressure conditions described above. 
     The other phase may also be made in situ in the reaction mass during the diamond growth. 
     The microstructure of the matrix can be manipulated in a number of ways such as by control of the cooling stage from the high temperature/pressure step, by subsequent heat treatment or by the inclusion of grain refining materials in the reaction mass. 
     As mentioned above, the diamond crystals present in the bonded, coherent material contain a high percentage of synthetic twinned diamonds. Examples of the twinned diamond crystals present in the material are illustrated by photographs  1  to  10 . FIGS. 1 to  7  are scanning electron micrographs and FIGS. 8 to  10  optical photographs, taken at between 30 and 150 times magnification. 
     FIGS. 2,  3 ,  4  and  6  are photographs of star twin diamond crystals from different angles. Star twinning is a form of cyclic twinning involving non-parallel {111} twin planes. Some of the {111} twin planes are identified in FIGS. 2,  3  and  6 . 
     FIG. 5 illustrates a cube crystal contact-twinned along a {111} plane. The corner at the top of the photograph is that of a cube—the three edges meeting at the point are mutually perpendicular. The {111} twin plane is identified. 
     FIG. 7 shows an aggregate of three intergrown twinned crystals. Two crystals (one almost vertical and the largest—almost horizontal) display polysynthetic twinning which involves a series of parallel composition planes. The crystal directed towards the viewer displays star twinning. Viewed end on, the crystal appears like a five sided star. 
     FIGS. 8 and 9 are photographs of synthetic macle twin plates from different angles. The high aspect ratio is to be noted. 
     FIG. 10 is a photograph of an elongate star twin diamond crystal. Again, the high aspect ratio is to be noted. 
     The invention will now be illustrated by the following examples. 
     EXAMPLE 1 
     A reaction capsule was used to produce a material comprising diamond crystals dispersed in an iron-cobalt matrix. A mixture was made of (a) 50 g diamond powder, with a maximum size of 8 microns and 50% by mass less than 1 micron, and (b) 285 g cobalt iron (65Co.35Fe) catalyst/solvent. The diamond was produced by crushing coarser synthetic material. The mixture was shaped into a cylinder, containing about 25% porosity, by hot pressing. The cylinder was placed in the reaction capsule and raised to conditions of about 55 kilobars and about 1380° C. The piece that was removed from the capsule was cylindrical in shape and the dimensions had been reduced in proportion to the reduction in porosity. Inside, the diamond material had grown to a size greater than 70 US mesh (210 microns) and was substantially all synthetic twinned diamond. The material which was bonded and coherent had a strength and abrasion resistance suitable for use in wear resistance and cutting applications. 
     EXAMPLE 2 
     A reaction capsule was used to produce a material comprising diamond crystals and tungsten carbide grains dispersed in an iron-cobalt matrix. A mixture was made of (a) 0.01 g diamond seeds, about 75 microns in size, (b) 42 g diamond powder, less than 0.5 micron in size, (c) 118 g eutectic tungsten carbide grains, between 40 and 60 US mesh (250 to 420 microns) in size, and (d) 240 g cobalt iron (65Co.35Fe) matrix powder. The diamond was produced by crushing coarser synthetic material. The mixture was shaped into a cylinder by hot pressing at 750° C. for 15 minutes. The cylinder, containing about 25% porosity, was placed in the reaction capsule and raised to conditions of about 55 kilobars and 1380° C. After removal from the capsule, the piece was cylindrical in shape, and the dimensions had been reduced in proportion to the reduction in porosity. Fracturing the piece revealed that the diamond source material had grown to a size greater than 70 US mesh (210 microns) and was substantially all synthetic twinned diamond. The tungsten carbide grains had remained at their original size. Furthermore, the diamond crystals and the tungsten carbide grains were well dispersed in the matrix. The material which was bonded and coherent had a strength and abrasion resistance suitable for use in wear resistance and cutting applications. 
     Similar twinned diamond-crystal containing materials produced by the Examples 1 and 2 were made using the method of the invention and different matrices. These Examples (3 to 18), and the conditions used, are set out in the table hereinafter. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 Source Size 
                   
                   
               
               
                   
                   
                 Pressure 
                 Temperature 
                 Time 
                 range 
                 Seed size 
                 Result 
               
               
                 Example 
                 Matrix 
                 (kbar) 
                 (° C.) 
                 (mins) 
                 (microns) 
                 (microns) 
                 Size (μm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3 
                 100% Co 
                 53.0 
                 1400 
                 660 
                 0-0.5 
                 none 
                 150-600 
               
               
                 4 
                 100% Ni 
                 54.8 
                 1410 
                 660 
                 0-0.5 
                 none 
                  200-1000 
               
               
                 5 
                 65Co.35Fe 
                 55.0 
                 1380 
                 1320  
                 0-0.5 
                 75 
                  70-600 
               
               
                 6 
                 65Co.35Fe 
                 53.0 
                 1370 
                 1020  
                 0-0.5 
                 65-75 
                 150-300 
               
               
                 7 
                 70Fe.30Ni 
                 55.0 
                 1430 
                 600 
                 6-12 
                 none 
                 10-20 
               
               
                 8 
                 70Fe.30Ni 
                 54.2 
                 1250 
                  60 
                 0-0.5 
                 none 
                  50-150 
               
               
                 9 
                 52Mn.48Ni 
                 54.2 
                 1410 
                 660 
                 0-0.5 
                 49-65 
                  80-200 
               
               
                 10 
                 56Cu.30Co.14Sn 
                 54.2 
                 1410 
                  40 
                 0-0.5 
                 49-65 
                 200-700 
               
               
                 11 
                 60Co.32Cu.8Sn 
                 54.2 
                 1410 
                 660 
                 0-0.5 
                 49-65 
                 200-700 
               
               
                 12 
                 40Cu.26Mn.24Ni.10Sn 
                 54.2 
                 1410 
                  40 
                 0-0.5 
                 49-65 
                 150-350 
               
               
                 13 
                 68Cu.17Sn.15Co 
                 54.2 
                 1410 
                 660 
                 0-0.5 
                 49-65 
                 up to 60 
               
               
                 14 
                 100% Cu 
                 54.2 
                 1420 
                 660 
                 0-0.5 
                 none 
                 up to 30 
               
               
                 15 
                 89Ni.LIP 
                 54.2 
                 1250 
                 660 
                 0-0.5 
                 none 
                  50-250 
               
               
                 16 
                 77Ni.13Cr.10P 
                 54.2 
                 1410 
                 660 
                 0-0.5 
                 none 
                 100-750 
               
               
                 17 
                 80Cu.20Sn 
                 55.0 
                 1460 
                 660 
                 0-0.5 
                 nane 
                 up to 30 
               
               
                 18 
                 60Cu.40Sn 
                 55.0 
                 1460 
                 660 
                 0-0.5 
                 none 
                 up to 30 
               
               
                   
               
             
          
         
       
     
     Examples of twinned diamond-crystal containing materials produced by the method of the invention, but using different source sizes and diamond types, are set out in Examples 19 to 26. In these examples and in examples 27 to 54, an iron nickel or cobalt iron catalyst/solvent was used. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Source size 
                   
                 Pressure 
                 Temperature 
                 Time 
                 Result 
               
               
                 Example 
                 (microns) 
                 Source type 
                 (kbar) 
                 (° C.) 
                 (mins) 
                 Size (μm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 19 
                   0-0.5 
                 synthetic 
                 54.2 
                 1220 
                 60 
                  50-150 
               
               
                 20 
                 0.5-1.0 
                 synthetic 
                 54.2 
                 1220 
                 60 
                 up to 30 
               
               
                 21 
                 1.0-2.0 
                 synthetic 
                 54.5 
                 1330 
                 600 
                 20-60 
               
               
                 22 
                 3-6 
                 synthetic 
                 54.5 
                 1330 
                 600 
                 10-20 
               
               
                 23 
                  6-12 
                 svnthetic 
                 55.0 
                 1430 
                 600 
                 10-20 
               
               
                 24 
                  8-16 
                 synthetic 
                 56.0 
                 1460 
                 600 
                 200-400 
               
               
                 25 
                 0.04 
                 shock wave 
                 54.5 
                 1380 
                 660 
                 up to 80 
               
               
                 26 
                   0-0.5 
                 natural 
                 54.5 
                 1380 
                 660 
                 200-400 
               
               
                   
               
             
          
         
       
     
     As pointed out above, the matrix of the diamond-crystal containing material may contain another or third phase material. Various third phase materials, in various forms, may be used to produce twinned diamond-crystal containing materials of the invention. The conditions and materials used in these examples, namely, Examples 27 to 29, are set out hereinafter. 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 Example 
                 27 
                 28 
                 29 
               
               
                   
               
             
             
               
                 Diamond source 
                 natural 
                 synthetic 
                 synthetic 
               
               
                 type 
               
               
                 Source size (μm) 
                 0.5-1.0 
                 1.0-2.0 
                 1.0-2.0 
               
               
                 Seed type 
                 none 
                 synthetic 
                 synthetic 
               
               
                   
                   
                 diamond 
                 diamond 
               
               
                 Seed size 
                   
                 67-75 
                 65-75 
               
               
                 (μm) 
               
               
                 Pressure 
                 54.2 
                 55.2 
                 55.2 
               
               
                 (kbar) 
               
               
                 Temperature (° C.) 
                 1390 
                 1370 
                 1370 
               
               
                 Time (mins) 
                 180 
                 600 
                 600 
               
               
                 Third phase 
                 WC-Co 
                 SiC 
                 SiC 
               
               
                   
                 (7,37%) 
               
               
                 Shape of third 
                 rounded 
                 platelets 
                 whiskers 
               
               
                 phase 
               
               
                 Result 
                 tungsten 
                 silicon carbide 
                 silicon carbide 
               
               
                   
                 carbide-cobalt 
                 platelets 
                 whiskers stable 
               
               
                   
                 stable, 
                 stable, 
                 diamond 
               
               
                   
                 diamond 
                 diamond 
                 crystals 
               
               
                   
                 crystals 
                 crystals 
                 twinned, 
               
               
                   
                 twinned, 
                 twinned, 
                 size 15-60 μm 
               
               
                   
                 size 20-40 μm 
                 size 10-20 μm 
               
               
                   
               
             
          
         
       
     
     A particularly useful third phase material has been found to be a carbide. Various carbides have been used in producing twinned diamond crystal containing materials and the conditions used are set out hereinafter (Examples 30 to 35). In each of these examples the carbide remained stable in the material produced. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Example 
                 30 
                 31 
                 32 
                 33 
                 34 
                 35 
               
               
                   
               
             
             
               
                 Source type 
                 synthetic 
                 synthetic 
                 synthetic 
                 natural 
                 synthetic 
                 synthetic 
               
               
                   
                 diamond 
                 diamond 
                 diamond 
                 diamond 
                 diamond 
                 diamond 
               
               
                 Source size 
                 0-0.5 
                 0.5-1.0 
                 0-0.5 
                 0-0.5 
                 1.0-2.0 
                 1.0-2.0 
               
               
                 (μm) 
               
               
                 Seed type 
                 synthetic 
                 none 
                 none 
                 none 
                 synthetic 
                 synthetic 
               
               
                   
                 diamond 
                   
                   
                   
                 diamond 
                 diamond 
               
               
                 Seed size 
                 65-75 
                   
                   
                   
                 65-75 
                 65-75 
               
               
                 (μm) 
               
               
                 Pressure 
                 53.0 
                 54.2 
                 54.2 
                 54.2 
                 55.2 
                 55.2 
               
               
                 (kbar) 
               
               
                 Temperature 
                 1370 
                 1390 
                 1390 
                 1390 
                 1370 
                 1370 
               
               
                 (° C.) 
               
               
                 Time (mins) 
                 660 
                 180 
                 180 
                 180 
                 600 
                 600 
               
               
                 Third phase 
                 eutectic 
                 WC-Co 
                 WC 
                 WC 
                 Cr 3 C 2   
                 SiC 
               
               
                   
                 WC/W 2 C 
               
               
                 Size of third 
                 250-420 
                 210-297 
                 38-88 
                 38-88 
                 less than 45 
                 105-125 
               
               
                 phase (μm) 
               
               
                 Result 
                 200-400 
                 up to 15 
                 up to 20 
                 30-60 
                 30-60 
                 10-20 
               
               
                 Size (μm) 
               
               
                   
               
             
          
         
       
     
     Other useful third phase materials are nitrides and oxides. Examples of the use of such third phase materials and the conditions used are set out hereinafter in Examples 36 to 41. In each of these examples, the diamond in the material was twinned and the nitride or oxide remained stable. 
     
       
         
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
             
             
               
                 Example 
                 36 
                 37 
                 38 
                 39 
               
               
                   
               
               
                 Diamond source type 
                 synthetic 
                 synthetic 
                 synthetic 
                 synthetic 
               
               
                 Source size (μm) 
                 1.0-2.0 
                 0.5-1.0 
                 1.0-2.0 
                 1.0-2.0 
               
               
                 Seed type 
                 synthetic diamond 
                 none 
                 synthetic diamond 
                 synthetic diamond 
               
               
                 Seed size (μm) 
                 65-75 
                   
                 67-75 
                 67-75 
               
               
                 Pressure (kbar) 
                 55.2 
                 55.2 
                 55.2 
                 55.2 
               
               
                 Temperature (° C.) 
                 1370 
                 1420 
                 1370 
                 1370 
               
               
                 Time (mins) 
                 600 
                 600 
                 600 
                 600 
               
               
                 Third phase 
                 Si 3 N 2   
                 cubic BN 
                 AlN 
                 TiN 
               
               
                 Size of third phase 
                 less than 10 
                 88-105 
                 less than 125 
                 less than 45 
               
               
                 in material (μm) 
               
               
                 Result Size (μm) 
                 up to 150 
                 10-20 
                 10-20 
                 10-30 
               
               
                   
               
             
          
           
               
                   
                 Example 
                 40 
                 41 
               
               
                   
                   
               
               
                   
                 Diamond source type 
                 synthetic 
                 synthetic 
               
               
                   
                 Source size (μm) 
                 1.0-2.0 
                 0.5-1.0 
               
               
                   
                 Seed type 
                 synthetic diamond 
                 none 
               
               
                   
                 Seed size (μm) 
                 65-75 
               
               
                   
                 Pressure (kbar) 
                 55.2 
                 55.2 
               
               
                   
                 Temperature (° C.) 
                 1370 
                 1420 
               
               
                   
                 Time (mins) 
                 600 
                 600 
               
               
                   
                 Third phase 
                 Al 2 O 3   
                 lime stabilised 
               
               
                   
                   
                   
                 zirconium dioxide 
               
               
                   
                 Size of third phase 
                 about 100 
                 less than 45 
               
               
                   
                 in material (μm) 
               
               
                   
                 Result - Size (μm) 
                 10-30 
                 10-20 
               
               
                   
                   
               
             
          
         
       
     
     Examples 42 to 46 illustrate methods of making twinned diamond crystal-containing materials using carbides and nitrides as a third phase and various sizes of diamond and third phase. The third phase material remained stable in the material produced. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Example 
                 42 
                 43 
                 44 
                 45 
                 46 
               
               
                   
               
             
             
               
                 Diamond source 
                 synthetic 
                 synthetic 
                 natural 
                 natural 
                 synthetic 
               
               
                 type 
               
               
                 Source size (μm) 
                 0.5-1.0 
                 0-0.5 
                 0-0.5 
                 0-0.5 
                 1.0-2.0 
               
               
                 Seed type 
                 none 
                 none 
                 none 
                 none 
                 synthetic 
               
               
                   
                   
                   
                   
                   
                 diamond 
               
               
                 Seed size (μm) 
                   
                   
                   
                   
                 65-75 
               
               
                 Pressure (kbar) 
                 54.2 
                 54.2 
                 54.2 
                 54.2 
                 55.2 
               
               
                 Temperature (° C.) 
                 1390 
                 1390 
                 1390 
                 1390 
               
               
                 Time (mins) 
                 180 
                 180 
                 180 
                 180 
                 600 
               
               
                 Third phase 
                 tungsten carbide 
                 tungsten 
                 tungsten carbide 
                 tungsten 
                 silicon 
               
               
                   
                 with 7.37% cobalt 
                 carbide 
                 with 7.37% cobalt 
                 carbide 
                 nitride 
               
               
                 Size of third phase 
                 210-297 
                 38-88 
                 210-297 
                 38-88 
                 less than 10 
               
               
                 in material (μm) 
               
               
                 Result - Size (μm) 
                 up to 20 
                 up to 20 
                 30-60 
                 30-60 
                 up to 150 
               
               
                   
               
             
          
         
       
     
     Examples using different concentrations of diamond and third phase in a twinned diamond crystal-containing material of the invention are shown in Examples 47 to 54. The third phase remained stable in the materials of each of these examples. 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Example 
                 47 
                 48 
                 49 
                 50 
               
               
                   
               
             
             
               
                 Diamond source 
                 synthetic 
                 synthetic 
                 synthetic 
                 synthetic 
               
               
                 type 
               
               
                 Source size (μm) 
                  0-0.5 
                   0-0.5 
                 8-16 
                 1.5-3.0 
               
               
                 Seed type 
                 none 
                 none 
                 none 
                 none 
               
               
                 Seed size (μm) 
               
               
                 Pressure (kbar) 
                 53.0 
                 55.0 
                 56.0 
                 54.2 
               
               
                 Temperature (° C.) 
                 1370 
                 1450 
                 1460 
                 1390 
               
               
                 Time (mins) 
                 660 
                 600 
                 600 
                 180 
               
               
                 Vol % diamond in 
                 35 
                 11 
                 53 
                 78 
               
               
                 material 
               
               
                 Third phase 
                 none 
                 none 
                 none 
                 none 
               
               
                 Vol % of third 
               
               
                 phase in material 
               
               
                 Result - Size (μm) 
                 200-1000 
                 200-600 
                 150-300  
                 200-800 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Example 
                 51 
                 52 
                 53 
                 54 
               
               
                   
               
             
             
               
                 Diamond source 
                 synthetic 
                 natural 
                 synthetic 
                 synthetic 
               
               
                 type 
               
               
                 Source size (μm) 
                   0-0.5 
                   0-0.5 
                 0.5-1.0 
                 1.0-2.0 
               
               
                 Seed type 
                 synthetic diamond 
                 none 
                 none 
                 synthetic 
               
               
                   
                   
                   
                   
                 diamond 
               
               
                 Seed size (μm) 
                 65-75 
                   
                   
                 65-75 
               
               
                 Pressure (kbar) 
                 53.0 
                 54.2 
                 54.2 
                 54.2 
               
               
                 Temperature 
                 1370 
                 1390 
                 1390 
                 1370 
               
               
                 (° C.) 
               
               
                 Time (mins) 
                 660 
                 180 
                 180 
                 600 
               
               
                 Vol % diamond 
                 8 
                 15 
                 31 
                 16 
               
               
                 in material 
               
               
                 Third phase 
                 eutectic tungsten 
                 tungsten 
                 tungsten 
                 silicon 
               
               
                   
                 carbide mixture 
                 carbide 
                 carbide with 
                 carbide 
               
               
                   
                   
                   
                 7.37% cobalt 
               
               
                 Vol % of third 
                 30 
                 30 
                 10 
                 26 
               
               
                 phase in material 
               
               
                 Result - Size (μm) 
                 up to 200 
                 30-60  
                 up to 15 
                 10-20 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 55 
     In another example, a reaction capsule was used to produce a material comprising twinned diamond crystals and chromium carbide fibres dispersed in a matrix of nickel/phosphorus containing a small quantity of chromium. The chromium carbide fibres were formed in situ by the chemical reaction of chromium metal in the matrix and carbon in solution from the diamond. A mixture was made of (a) 70 volume percent nickel/chromium/phosphorus alloy powder, and (b) 30 volume percent diamond powder with a size range less than 0.25 microns. The mixture was shaped into a cylinder, containing about 20% porosity, by hot pressing. The cylinder was placed in the reaction capsule and raised to conditions of about 54.2 kbars and about 1420° C., and the conditions maintained for a period of about 11 hours. The piece that was recovered from the capsule remained cylindrical in shape, and its dimensions had been reduced in proportion to the reduction in porosity. Upon examination of the recovered material, fibres of chromium carbide, of approximately hexagonal cross section and with a length of up to 500 microns and about 30 microns across, were found dispersed amongst the grown diamonds. These diamonds were twinned and ranged in size from about 100 to 750 microns.