High density polycrystalline superhard material

Abstract

A polycrystalline superhard material comprises a mass of diamond, graphite or cubic boron nitride particles or grains bonded together by ultrathin inter-granular bonding layers, the inter-granular bonding layers having an average thickness of greater than about 0.3 nm and less than about 100 nm. There is also disclosed a method for making such a polycrystalline superhard material.

1 . A polycrystalline superhard material comprising a mass of diamond, graphite or cubic boron nitride particles or grains bonded together by ultrathin inter-granular bonding layers, the inter-granular bonding layers having an average thickness of greater than about 0.3 nm and less than about 100 nm. 
     
     
         2 . A polycrystalline superhard material according to  claim 1 , wherein the average thickness of the inter-granular bonding layers is less than 20 nm. 
     
     
         3 . A polycrystalline superhard material according to  claim 1 , wherein the average thickness of the inter-granular bonding layers is less than 10 nm. 
     
     
         4 . A polycrystalline superhard material according to  claim 1 , wherein the average particle size of the diamond or cubic boron nitride particles or grains is from about 50 nanometres to about 50 microns. 
     
     
         5 . A polycrystalline superhard material according to  claim 1 , wherein the polycrystalline superhard material comprises diamond and the inter-granular bonding layers comprise diamond. 
     
     
         6 . A polycrystalline superhard material according to  claim 1 , wherein the polycrystalline superhard material comprises diamond and the inter-granular bonding layers comprise one or more carbides of one or more bonding elements selected from the group comprising Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and Ge and compounds or alloys of these. 
     
     
         7 . A polycrystalline superhard material according to  claim 1 , wherein the polycrystalline superhard material comprises diamond and the inter-granular bonding layers comprise SiC. 
     
     
         8 . A polycrystalline superhard material according to  claim 1 , wherein the polycrystalline superhard material comprises cBN and the inter-granular bonding layers comprise cBN. 
     
     
         9 . A polycrystalline superhard material according to  claim 1 , wherein the polycrystalline superhard material comprises cBN and the inter-granular bonding layers comprise one or more borides and/or nitrides of one or more bonding elements selected from the group comprising Be, Mg, Ca, Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B, Al, Ga, In, C, Si, Ge, Sn, Pb, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and compounds or alloys of these. 
     
     
         10 . A method for making polycrystalline superhard material, the method including providing a mass of diamond, grahite or cubic boron nitride particles or grains, depositing ultrathin layers of a bonding material on respective diamond, graphite or cubic boron nitride particles or grains, the bonding material being selected so as to be capable of forming bonds with the diamond, graphite or cubic boron nitride particles or grains, the average thickness of the deposited layers of bonding material being greater than about 0.5 nm and less than about 200 nm, consolidating the diamond, graphite or cubic boron nitride particles or grains and bonding material to form a green body, and subjecting the green body to a temperature and pressure at which the diamond, graphite or cubic boron nitride is thermodynamically stable, sintering and forming polycrystalline superhard material. 
     
     
         11 . A method according to  claim 10 , wherein the average thickness of the deposited layers of bonding material is less than about 100 nm. 
     
     
         12 . A method according to  claim 10 , wherein the average thickness of the deposited layers of bonding material is less than about 50 nm. 
     
     
         13 . A method according to  claim 10 , wherein the average particle size of the diamond, graphite or cubic boron nitride particles or grains prior to deposition of the bonding material is from about 50 nanometres to about 50 microns. 
     
     
         14 . A method according to  claim 10 , wherein the polycrystalline superhard material comprises diamond and the bonding material is graphite or other non-diamond carbon. 
     
     
         15 . A method according to  claim 10 , wherein the polycrystalline superhard material comprises diamond and the bonding material comprises a carbide former selected from the group comprising Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and Ge and compounds or alloys of these. 
     
     
         16 . A method according to  claim 10 , wherein the polycrystalline superhard material comprises diamond and the bonding material comprises Si or SiC. 
     
     
         17 . A method according to any one of  claims 10  to  13   claim 10 , wherein the polycrystalline superhard material comprises cBN and the bonding material comprises hBN. 
     
     
         18 . A method according to  claim 10 , wherein the polycrystalline superhard material comprises cBN and the bonding material comprises a boride and/or nitride former selected from the group comprising Be, Mg, Ca, Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B, Al, Ga, In, C, Si, Ge, Sn, Pb, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and compounds or alloys of these. 
     
     
         19 . A method according to  claim 10 , wherein the step of subjecting the green body to a pressure comprises subjecting the green body to a pressure of between about 5 GPa or more, or 6.8 GPa or more, or 7.7 GPa or more, or between about 8 GPa to about 18 GPa. 
     
     
         20 . A wear element comprising a polycrystalline superhard material according to  claim 1 .