Superhard structure and method of making same

Abstract

A superhard structure comprises a body of polycrystalline superhard material comprising a first region and a second region, the second region being adjacent an exposed surface of the superhard structure, the second region comprising a diamond material or cubic boron nitride, the density of the second region being greater than 3.4×103 kilograms per cubic metre when the second region comprises diamond material. The material(s) forming the first and second regions have a difference in coefficient of thermal expansion, the first and second regions being arranged such that this difference induces compression in the second region adjacent the exposed surface. The first/a further region has the highest coefficient of thermal expansion of the polycrystalline body and is separated from a peripheral free surface of the body of polycrystalline superhard material by the second region or one or more further regions formed of a material or materials of a lower coefficient of thermal expansion. The regions comprise a plurality of grains of polycrystalline superhard material. There is also disclosed a method of making such a material.

1 . A superhard structure comprising:
 a body of polycrystalline superhard material comprising:   a first region; and   a second region, the second region being adjacent an exposed surface of the superhard structure, the second region comprising a diamond material or cubic boron nitride, the density of the second region being greater than 3.4×10 3  kilograms per cubic metre when the second region comprises diamond material; and   wherein the material or materials forming the first and second regions have a difference in coefficient of thermal expansion, the first and second regions being arranged such that the difference between the coefficients of thermal expansion induces compression in the second region adjacent the exposed surface; and wherein the first region or a further region has the highest coefficient of thermal expansion of the polycrystalline body and is separated from a peripheral free surface of the body of polycrystalline superhard material by the second region or one or more further regions formed of a material or materials of a lower coefficient of thermal expansion, wherein the regions comprise a plurality of grains of polycrystalline superhard material.   
     
     
         2 . A superhard structure as claimed in  claim 1 , wherein the first region and the second region have one or more further differences in physical properties. 
     
     
         3 . A superhard structure as claimed in  claim 2 , wherein the one or more further differences in physical properties comprises a difference in the modulus of elasticity of the material(s) forming the first and second regions. 
     
     
         4 . A superhard structure as claimed in any one of the preceding claims, wherein the body of polycrystalline superhard material comprises polycrystalline diamond material. 
     
     
         5 . A superhard structure according to any one of the preceding claims, further comprising a substrate bonded to a face of the body of polycrystalline material along an interface. 
     
     
         6 . A superhard structure according to  claim 5 , wherein the substrate is formed of a carbide material. 
     
     
         7 . A superhard structure according to any one of  claim 5  or  6 , further comprising a third region, a fourth region, a fifth region and a sixth region, the first to sixth regions being axisymmetric, the second to sixth regions being adjacent the first region and each second to sixth region having a lower coefficient of thermal expansion than the first region; wherein:
 a) the first region is positioned between the second region and the substrate; 
 b) the third region being adjacent to the first region and at the interface of the substrate and the body of polycrystalline material, the third region being located at and forming a portion of the peripheral free surface of the body of polycrystalline material and between the first region and the substrate; 
 c) the fourth region being adjacent to the third region and situated at the peripheral free surface of the polycrystalline superhard material; 
 d) the fifth region being adjacent to the fourth region and the second region and separating the second region from the fourth region; 
 e) the sixth region being adjacent to the first region and separating the first region from the substrate. 
 
     
     
         8 . A superhard structure according to  claim 7 , wherein each of the second to the sixth regions are made of one or more materials of differing coefficients of thermal expansion. 
     
     
         9 . A superhard structure according to  claim 7 , wherein the sixth region is formed of a material having the highest coefficient of thermal expansion in the superhard structure. 
     
     
         10 . A superhard structure according to  claim 9 , wherein the materials from which the first, second, third, fourth, and fifth regions are formed have differing coefficients of thermal expansion. 
     
     
         11 . A superhard structure according to  claim 7 , wherein the first and sixth regions are formed of the same material and have the highest coefficient of thermal expansion, the material from which the first and sixth regions are formed having a higher coefficient of thermal expansion than the material or materials from which the second, third, fourth, and fifth regions are formed. 
     
     
         12 . A superhard structure according to  claim 7 , wherein second, third, fourth, and fifth regions are formed of one or more materials having differing coefficients of thermal expansion. 
     
     
         13 . A superhard structure according to any one of  claims 5  to  12 , wherein the first region is formed of a material having the highest coefficient of thermal expansion of the materials in the superhard structure, the first region being situated substantially symmetrically around the central axis of the superhard structure at the interface of the body polycrystalline material and the substrate and separated from the free surfaces of the superhard material by the second region, the second region being formed of a material having the lowest coefficient of thermal expansion in the superhard structure. 
     
     
         14 . A superhard structure according to  claim 13 , wherein the first region is subdivided into more than one separate volume, all of the volumes being separated from the peripheral free surface of the superhard structure by at least one material of lower coefficient of thermal expansion. 
     
     
         15 . A superhard structure according to  claim 14  wherein one or more of the separate volumes are formed of a material having the highest coefficient of thermal expansion in the superhard structure and are toroidal. 
     
     
         16 . A superhard structure according to any one of the preceding claims, further comprising a third volume between the first and second regions, the third volume being formed of a material having a coefficient of thermal expansion different from that of the material from which the second region is formed. 
     
     
         17 . A superhard structure according to  claim 16 , wherein the third volume is formed from a material having a coefficient of thermal expansion intermediate that of the material forming the second region and the region(s) having the highest coefficient of expansion material in the superhard structure. 
     
     
         18 . A superhard structure according to  claim 17 , wherein one or more of the toroidal volumes formed of the material of highest coefficient of thermal expansion are segmented having one or more discontinuities. 
     
     
         19 . A superhard structure according to any one of the preceding claims, further comprising one or more segments of material attached to a portion of the peripheral free edge adjoined and abutted by the body of polycrystalline material. 
     
     
         20 . A superhard structure according to any one or the preceding claims, wherein the volume of the region formed of the material having the highest coefficient of thermal expansion material occupies between around 30% to 95% of the total volume of the body of polycrystalline material. 
     
     
         21 . A superhard structure according to any one of the preceding claims, wherein the coefficient of thermal expansion of the material having the highest coefficient of thermal expansion differs from the coefficient of thermal expansion of the material in an adjacent region by at least about 0.3×10 −6  per degree Centigrade. 
     
     
         22 . A superhard structure according to  claim 21 , wherein the body of polycrystalline material is polycrystalline diamond material, and the region formed of the material having the highest coefficient of thermal expansion is formed from a polycrystalline diamond material having the highest metal content relative to the polycrystalline diamond material(s) in the other regions. 
     
     
         23 . A superhard structure according to  claim 22 , wherein the metal content in the polycrystalline diamond materials in each volume is around 10 volume percent or less. 
     
     
         24 . A superhard structure according to any one of  claim 22  or  23 , wherein the difference in metal content between the regions is at least about 1.0 volume percent. 
     
     
         25 . A superhard structure according to any one of the preceding claims, wherein the body of polycrystalline material comprises a metal component, the metal component being a transition metal alloy. 
     
     
         26 . A superhard structure according to any one of  claims 1  to  24 , wherein the body of polycrystalline material comprises a metal component, the metal component being a cobalt alloy. 
     
     
         27 . A superhard structure according to any one of the preceding claims, wherein the body of polycrystalline material comprises a metal component, wherein the metal component is an alloy having a coefficient of thermal expansion of less than about 4×10 −6  per degree Centigrade. 
     
     
         28 . A superhard structure according to any one of the preceding claims, wherein the body of polycrystalline material comprises a metal component, the metal component containing a second phase of a material which modifies the coefficient of thermal expansion of the polycrystalline material. 
     
     
         29 . A superhard structure according to  claim 28 , wherein the second phase material comprises a metal carbide. 
     
     
         30 . A superhard structure according to  claim 29 , wherein the metal carbide comprises tungsten carbide or silicon carbide. 
     
     
         31 . A superhard structure according to  claim 28 , wherein the second phase comprises an oxide ceramic. 
     
     
         32 . A superhard structure according to  claim 31 , wherein the oxide ceramic comprises one or more of alumina, Al 2 O 3 , zirconia, ZrO 2 . 
     
     
         33 . A superhard structure according to any one of the preceding claims, wherein one or more of the regions is formed of a diamond containing composite material. 
     
     
         34 . A superhard structure according to  claim 33 , wherein the composite material comprises a diamond-ceramic composite material. 
     
     
         35 . A superhard structure according to  claim 1 , wherein the body of polycrystalline material comprises more than three regions formed of materials differing in coefficients of thermal expansion and wherein boundaries between said regions are substantially parallel and said regions are of the same geometric form. 
     
     
         36 . A superhard structure according to any one of the preceding claims, wherein the coefficients of thermal expansion changes in a gradual manner across the adjacent regions of the body of polycrystalline material. 
     
     
         37 . A superhard structure according to  claim 5 , wherein the interface between the body of polycrystalline material and the substrate is non planar. 
     
     
         38 . A superhard structure according to  claim 5 , wherein the interface between the body of polycrystalline material and the substrate is generally convex. 
     
     
         39 . A superhard structure according to any one of the preceding claims, wherein the body of polycrystalline material has a chamfered peripheral edge. 
     
     
         40 . A superhard structure according to any one of the preceding claims, wherein a portion or the whole of the free surface of the body of polycrystalline material comprises a layer in which metal content has been removed either in whole or in part. 
     
     
         41 . A superhard structure according to any one of the preceding claims, wherein a portion or the whole of the free surface of the body of polycrystalline material comprises a layer in which metal content has been removed either in whole or in part to a depth of between 50 microns and 500 microns. 
     
     
         42 . A superhard structure according to any one of the preceding claims, wherein the superhard structure has been subjected to a stress relieving heat treatment in a temperature range 550 to 750° C. 
     
     
         43 . A method for making a polycrystalline superhard structure comprising:
 a) forming a first region of polycrystalline material;   b) forming a second region of polycrystalline material adjacent the first region and as an exposed surface, the second region comprising polycrystalline diamond or cubic boron nitride; wherein the material(s) forming the first and second regions have one or more differences in physical properties;   c) subjecting the first and second regions to a pressure greater than 4 GPa and a temperature greater than 1200° C. for a predetermined time; and   d) reducing the pressure and temperature to ambient conditions such that the one or more differences between the physical properties induces compression in the second region adjacent the exposed surface; wherein the first region or a further region has the highest coefficient of thermal expansion of the polycrystalline body and is separated from a peripheral free surface of the body of polycrystalline superhard material by the second region or one or more further regions formed of a material or materials of a lower coefficient of thermal expansion, wherein the regions comprise a plurality of grains of polycrystalline superhard material.   
     
     
         44 . A method as claimed in  claim 43 , wherein the one or more differences in physical properties is a difference in the coefficient of thermal expansion and/or a difference in the modulus of elasticity of the material(s) forming the first and second regions. 
     
     
         45 . A method as claimed in any one of  claim 43  or  44 , further comprising; prior to the steps of subjecting the first and second regions to a pressure and temperature, placing the first region, the second region and a substrate into a container; and wherein the step of subjecting the first and second regions to a pressure and temperature comprises subjecting the container containing the first and second region and the substrate to said pressure and temperature. 
     
     
         46 . A method as claimed in  claim 45 , wherein the step of placing a substrate into the container comprises placing a substrate formed of cemented metal carbide into the container. 
     
     
         47 . A method as claimed in  claim 46 , wherein the step of placing a substrate into the container comprises placing a substrate formed of cobalt cemented tungsten carbide into the container. 
     
     
         48 . A method according to any one of  claims 45  to  47 , further comprising forming a third region, a fourth region, a fifth region and a sixth region, the first to sixth regions being axisymmetric, the second to sixth regions being adjacent the first region and each second to sixth region having a lower coefficient of thermal expansion than the first region. 
     
     
         49 . A method according to  claim 48 , comprising:
 a. positioning the first region between the second region and the substrate;   b. positioning the third region adjacent the first region and at the interface of the substrate and the body of polycrystalline material, the third region being located at and forming a portion of the peripheral free surface of the body of polycrystalline material and between the first region and the substrate;   c. positioning the fourth region adjacent to the third region and situated at the peripheral free surface of the polycrystalline superhard material;   d. positioning the fifth region adjacent to the fourth region and the second region and separating the second region from the fourth region; and   e. positioning the sixth region adjacent to the first region and separating the first region from the substrate.   
     
     
         50 . A drill bit or a cutter or a component therefor comprising the superhard structure of any one of  claims 1  to  42 . 
     
     
         51 . A method of forming a superhard structure substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings. 
     
     
         52 . A superhard structure substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings. 
     
     
         53 . A drill bit or a cutter or a component therefor substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings.