GB2486973A

GB2486973A - A polycrystalline superhard material

Info

Publication number: GB2486973A
Application number: GB1121905.2A
Authority: GB
Inventors: Mehmet Serdar Ozbayraktar
Original assignee: Element Six Abrasives SA
Current assignee: Element Six Abrasives SA
Priority date: 2010-12-29
Filing date: 2011-12-20
Publication date: 2012-07-04
Anticipated expiration: 2031-12-20
Also published as: GB2486973B; GB201121905D0; GB201022033D0; WO2012089565A1; US20130337248A1

Abstract

A polycrystalline superhard material is disclosed which comprises a mass of diamond, graphite or cubic boron nitride particles or grains bonded together by ultrathin intergranular bonding layers, the inter-granular bonding layers having an average thickness of greater than about 0.3 nm and less than about 100 nm. The bonding layers may comprise diamond, carbides including SiC, borides or nitrides including cBN. The material may be used as a wear element. There is also disclosed a method for making such a polycrystalline superhard material.

Description

HIGH DENSITY POLYCRYSTALL1NE SUPERHARD MATERIAL

Field

This disclosure relates to a high density polycrystalline superhard material, a method of making high density polycrystalline superhard material, and to a wear element comprising a high density polycrystalline superhard material.

Background

Cutter inserts for machine and other tools may comprise a layer of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) bonded to a cemented carbide substrate. PCD and PCBN are examples of superhard materials, also called superabrasive materials, which have a hardness value substantially greater than that of cemented tungsten carbide.

Components comprising PCD are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. PCD comprises a mass of substantially inter-grown diamond grains forming a skeletal mass, which defines interstices between the diamond grains. PCD material comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 CPa and temperature of at least about 1,200 degrees centigrade in the presence of a sintering aid, also referred to as a catalyst material for diamond. Catalyst material for diamond is understood to be material that is capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite. Some catalyst materials for diamond may promote the conversion of diamond to graphite at ambient pressure, particularly at elevated temperatures. Examples of catalyst materials for diamond are cobalt, iron, nickel and certain alloys including any of these. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. The interstices within PCD material may at least partly be filled with the catalyst material.

A well-known problem experienced with this type of PCD material, however, is that the residual presence of the catalyst material for diamond, in particular a metallic catalyst material for diamond, for example Co, Ni or Fe, in the interstices has a detrimental effect on the performance of the POD material at high temperatures. During application, the POD material heats up and thermally degrades, largely due to the presence of the metallic catalyst material that catalyses graph itisation of the diamond and also causes stresses in the POD material due to the large difference in thermal expansion between the metallic catalyst material and the diamond microstructure.

Oomponents comprising PCBN are used principally for machining metals.

PCBN material comprises a sintered mass of cubic boron nitride (cBN) grains.

The cBN content of POBN materials may be at least about 40 volume %.

When the cBN content in the POBN is at least about 70 volume % there may be substantial direct contact among the cBN grains. When the cBN content is in the range from about 40 volume % to about 60 volume % of the compact, then the extent of direct contact among the cBN grains is limited. POBN may be made by subjecting a mass of cBN grains together with a powdered matrix phase, to a temperature and pressure at which the cBN is thermodynamically more stable than the hexagonal form of boron nitride, hBN.

GB 2 453 023 discloses an ultra-hard composite construction comprising an ultra-hard body having a plurality of diamond crystals bonded to one another by a carbide reaction product. The carbide reaction product is formed from a carbide former selected from silicon, boron, titanium, molybdenum or vanadium with diamond at HPHT conditions. The ultra-hard body resulting from the HPHT process comprises in the range of from about 40 to 90 percent by volume diamond. The body may include a further diamond region positioned along a surface portion of the body and that is substantially exclusively diamond, having a diamond content of 95 to 99 percent or more.

There is a need for a high density polycrystalline superhard material comprising diamond or cubic boron nitride which has a high thermal stability, thereby enabling high cutting speeds in cutting applications as well as longer cutter lifetimes in drilling applications, and greater toughness, all without the need for using excessive pressures and temperatures.

Summary

Viewed from a first aspect there is provided a polycrystalline superhard material comprising a mass of diamond, graphite or cubic boron nitride particles or grains bonded together by one or more 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. Such ultrathin bonding layer(s) may improve toughness.

In some embodiments, the average thickness of the inter-granular bonding layers is less than about 20 nm, or less than about 10 nm, or less than about Snm.

The average particle size of the diamond or cubic boron nitride particles or grains is from about 50 nanometres to about 50 microns.

The diamond content of the polycrystalline diamond material may, in some embodiments, be at least about 90 percent, at least about 95 percent, or at least about 99 percent of the volume of the polycrystalline superhard material.

In some embodiments, the content of the inter-granular bonding material is at most about 10 volume percent, at most about 5 volume percent, or at most about I volume percent of the polycrystalline superhard material.

Viewed from a further aspect, there is provided a method for making polycrystalline superhard material, the method comprising providing a mass of diamond, graphite 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.

The diamond particles or grains, prior to deposition of the bonding material, may have, for example, an average particle or grain size of from about 50 nanometres to about 50 microns.

In some embodiments, a multimodal mixture of diamond particles or grains of varying average particle or grain size may be provided.

In some embodiments, the polycrystalline superhard material may be a stand-alone compact or the polycrystalline superhard material may be attached to a substrate.

Sintering may be carried out at pressures of, for example, about 2.5 CPa or more, or 5 CPa or more, or 6.8 CPa or more, or 7.7 CPa or more, for example between about 8CPa to about 1 8GPa and temperatures of about 450 degrees centigrade or more, or 1500 degrees centigrade or more, or 2250 degrees centigrade or more, or 2400 degrees centigrade or more, for sintering times of seconds or more, or 3 minutes or more, or 30 minutes or more.

Viewed from another aspect, there is provided a wear element comprising a polycrystalline superhard material as described herein.

Detailed Description

As used herein, "high density polycrystalline diamond material" comprises a mass of diamond particles or grains, a substantial portion of which are bonded to one another and in which the content of diamond is at least about 90 volume percent of the material.

As used herein, "high density polycrystalline cubic boron nitride material" comprises a mass of cubic boron nitride grains, a substantial portion of which are bonded to one another and in which the content of cubic boron nitride is at least about 90 volume percent of the material.

As used herein, "epitaxy" in its broadest sense is understood to include, but not limited to, the deposition of a polycrystalline or a monocrystalline layer of bonding material. The epitaxy may be "heteroepitaxy", which is understood to mean that the superhard material and deposited layers of bonding material contain different components, or "homoepitaxy", which is understood to mean that the superhard material and deposited layers of bonding material contain the same components.

A "multi-modal size distribution of a mass of grains" is understood to mean that the grains have a size distribution with more than one peak, each peak corresponding to a respective "mode". Multimodal polycrystalline bodies are typically made by providing more than one source of a plurality of grains, each source comprising grains having a substantially different average size, and blending together the grains or particles from the sources. Measurement of the size distribution of the blended grains typically reveals distinct peaks corresponding to distinct modes. When the grains are sintered together to form the polycrystalline body, their size distribution is further altered as the grains are compacted against one another and fractured, resulting in the overall decrease in the sizes of the grains. Nevertheless, the multimodality of the grains is usually still clearly evident from image analysis of the sintered article.

As used herein, a "green body" is an article that is intended to be sintered or which has been partially sintered, but which has not yet been fully sintered to form an end product. It may generally be self-supporting and may have the general form of the intended finished article.

As used herein, a "superhard wear element" is an element comprising a superhard material and is for use in a wear application, such as degrading, boring into, cutting or machining a workpiece or body comprising a hard or abrasive material.

A polycrystalline superhard material is described having a high density of diamond or cubic boron nitride in its polycrystalline structure. In some embodiments, a high-purity PCD or PCD-Iike material with high diamond density, high degree of bonding, very little or no free elements or compounds present and high fracture toughness is provided. In some embodiments, an analogous high density PCBN material is provided.

In the case of PCD, in some embodiments, a mass of diamond particles or grains is provided. A layer of very thin bonding material is deposited on respective diamond particles or grains using a suitable method such as sol-gel deposition. To achieve homoepitaxy, the bonding materials are carbon allotropes such as graphite, graphene or diamond-like carbon, for example, and to achieve heteroepitaxy the bonding materials are carbide-forming elements such as silicon or suitable metals or alloys, for example.

The starting mass is sintered at elevated temperature and pressure conditions as needed for the sintered diamond to be more thermodynamically stable than graphite. Typically, sintering takes place at a pressure in excess of about 5 CPa and a temperature in excess of about 140000. However, it will be understood by a person skilled in the art that suitable conditions from low pressure (for instance about 2.5 CPa) to about 10 CPa or more (even up to CPa) and modest temperature (for instance about 450°C) to about 2400°C or more in the diamond-stable region can be used to convert the nano-sized carbon allotrope to diamond or to cause reaction of the diamond grains with the carbide-former to form inter-granular bonded layers of from a few to about atoms thick. In some embodiments, the pressure conditions are from about 8 CPa to about 10 CPa or, in other embodiments about 8CPa to about I8CPa.

Excellent bonding in the sintered mass may be achieved by means of very thin bonded layers of bonding material that form between the diamond particles or grains, these inter-granular layers ranging from a few atoms to tens of atoms in thickness. The resultant material may be highly thermally-stable and tough. Furthermore utilising reaction bonding as defined above, may result in a reduction in pressure requirement compared with direct diamond to diamond conversion which would have significant implications for commercialisation as cost increases very rapidly and achievable product size decreases significantly as the pressure requirement is increased.

In the case of graphite or other non-diamond carbon as the bonding material, direct conversion of the very thin layers of deposited bonding material to diamond will result at sufficient pressure and temperature, resulting in POD where the inter-granular layers have the diamond structure and hence no mismatch on the particle-layer boundary is expected. In the case of carbide-forming elements being used as the bonding material, for example silicon or suitable metals or alloys, reaction-bonded POD is formed at sufficient pressure and temperature and the very thin carbide inter-granular layers will be constrained by the neighbouring diamond particles to have a structure closer to that of diamond than that of the free carbide and to have small misfit with the diamond lattice.

As a very high percentage volume of the starting material is already-formed diamond, the need is therefore to transform very small amounts of carbon, or to react very small amounts of carbide forming elements or alloys, at the grain boundaries.

The very thin layers of bonding material may be arranged on the diamond grains using methods such as, but not limited to, sot-gel, physical vapour deposition, chemical vapour deposition, atomic layer deposition, liquid-phase epitaxy, solid-phase epitaxy, molecular-beam epitaxy or magnetron sputtering.

The layers may partially or completely cover the diamond grains.

In some embodiments, the average size of the starting diamond particles or grains may range from about 50 nm to about 50 microns. The average thickness of the starting graphitic, other carbon or carbide-forming very thin bonding material layers may range from, for example, about 0.5 nm to about 200 nm. The carbon binder source may be graphite, or glassy carbon, or graphene, or any type of fullerene, or diamond-like carbon. The carbide forming bonding elements may be chosen from, for example, Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and Ge. In some embodiments, the bonding material may be silicon or silicon carbide.

Combinations (mixtures, alloys, compounds and the like) of two or more of the carbon binder sources or two or more of the carbide-forming elements or two or more of the carbides may be used. In some embodiments, the purity of the starting materials is selected to assist in the production of PCD with very small flaw sizes thereby not only improving strength but leading to the option of transparent PCD material.

In some embodiments, the average thickness of the newly grown inter-granular bonded layers may vary from less than 1 nm, typically from about 0.3 nm, to less than about 100 nm, or less than about 20 nm, or less than about nm, or less than about 5 nm. The bonded layer material may be diamond, or a carbide constrained by neighbouring diamond grains to have a crystal structure closer to that of diamond than to that of the free carbide, and small amounts of the carbide-forming elements or alloys may be present.

In the case of a carbide bonded layer a low degree of misorientation between the diamond grain and the newly formed layer is expected due to the layer being very thin, i.e. a misfit angle of less than approximately 11 degrees is expected. The carbides have higher coefficient of thermal expansion than diamond, so the diamond grains in the final product should be under compressive stress, hence the carbide neck should be in tension favouring intergranular crack propagation. This should act as a toughening mechanism.

Toughness is further enhanced by the nanosized nature of the bonded inter-layer material. Greater fracture toughness will assist in the manufacture of higher precision cutting tools that display less edge chipping of the tool, giving a cleaner and more accurate cut and more impact resistance. Improved thermal stability is expected in all cases enabling increased cutting speeds and longer lifetime in drilling applications.

In some embodiments, the superhard material is cBN powder used to synthesise PCBN. The bonding material may be a boride and/or nitride former in the case of heteroepitaxy or it may be hBN in the case of homoepitaxy.

Where the superhard starting material is cBN powder, a similar approach to that described for PCD synthesis is followed. In this case very thin bonding material layers of nitride and/or boride formers are arranged on the primary cBN crystals. The bonding materials may be chosen from 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 or compounds / alloys of these. Alternatively the very thin bonding material layer may be hBN arranged on the cBN primary crystals and directly converted to PCBN under appropriate pressure and temperature conditions. Examples of carbide, nitride, boride and carbonitride binder compounds that can be used in some embodiments are TiC, TiB2, TiCN1 and TiN.

Preferred reaction-bonded compounds in the PCD or PCBN very thin bonded layer region may include but are not limited to: SiC, Si3N4, TiC, TiN, TaC, TaN, TiCN1, TaCN1, WC, WN2, NbC, Nb2C, and TiB2. It is also noted that compounds may be formed on the diamond or cBN particle or grain surfaces before sintering. This is because reactions may occur during the arrangement of the bonding material due to the elevated temperatures used in some of these processes.

A method for making polycrystalline superhard material comprises providing a mass of diamond or cubic boron nitride particles or grains, depositing ultrathin layers of a bonding material on respective diamond or cubic boron nitride particles or grains, the bonding material being selected so as to be capable of forming bonds with the diamond or cubic boron nitride particles or grains, and the average thickness of the deposited layers of bonding material being greater than about 0.5 nm and less than about 200 nm. The diamond or cubic boron nitride particles or grains and bonding material are consolidated into a green body, which green body is then subjected to a temperature and pressure at which the diamond or cubic boron nitride is more thermodynamically stable than graphite or hBN, respectively, in order to sinter it and form polycrystalline diamond or cubic boron nitride material.

Prior to deposition of the bonding material, the diamond or cubic boron nitride particles may have, for example, an average particle size ranging from about nanometres to about 50 microns.

The green body, once formed is placed in a suitable container and introduced into a high pressure high temperature press. Pressure and heat are applied in order to sinter the diamond particles together, typically at pressures of 2.5 CPa or more, or of 5 CPa or more, or of 6.8 CPa or more, or of 7.7 Cpa or more, and up to about 10 GPa, and temperatures of 450°C or more, or 1500°C or more, or 2250°C or more, or 2400°C or more, but in some embodiments the pressures may be up to around 25CPa.

Non-limiting examples of polycrystalline superhard materials will now be described.

Example I

g of crushed diamond of average particle size 0.75 micron may be cleaned by placing in a furnace and heating at 800 degrees centigrade for 1 hour in 10% hydrogen in an argon atmosphere. The diamond powder may then be transferred into a plasma reactor of the type typically used to deposit diamond-like carbon (DLC), and the diamond particles may be coated with a coating (not entirely uniform, but covering most of the surface of the diamond particles) of DLC of approximately 35 nm thickness. The coated diamond particles may be transferred to a capsule and subjected to approximately 8 CPa and 2000 degrees centigrade for approximately 30 seconds at dwell time. The sintered compact may be recovered from the capsule and high resolution scanning electron microscopy of a polished section is expected to show diamond grains connected by layers of diamond of approximately 4-12 nanometres thick. HRTEM analysis of the composite is expected to confirm that the layers have a diamond crystal structure. The diamond content of the sintered compact is expected to be close to 100% by volume.

Example 2

g of diamond of average particle size 2 microns may be cleaned by placing in a furnace and heating at 800 degrees centigrade for 1 hour in 10% hydrogen in an argon atmosphere. The diamond may then be transferred to a radio frequency plasma-enhanced chemical vapour deposition (rf PECVD) reactor and subjected to standard conditions for silicon thin film deposition: the deposition temperature would typically be 200 degrees centigrade, and silane (SiH4) and hydrogen (H2) gases would be fed into the reactor to maintain a 811-14 partial pressure of 0.9 Torr and a [H2J:[SiH4 ratio of 80. The ri power flux would be set at 70 mW/cm2. After a deposition time of 500 seconds, the gases would be purged from the reactor with argon, the reactor cooled and the diamond recovered. 2 g of the diamond, now coated with a silicon layer of approximately 50 nanometres thick, may then be placed in a capsule in a glove box under argon atmosphere to prevent oxidation of the silicon layer. The capsule may be pressed in a high-pressure high-temperature press at 8 CPa and 1800 degrees centigrade for approximately seconds dwell time at condition. The sintered compact may be recovered from the capsule and high resolution scanning electron microscopy of a polished section is expected to show diamond grains connected by layers of silicon carbide of approximately 4-15 nanometres thick. Analysis of the composite using X-ray diffraction and the Scherrer calculation is expected to indicate the silicon carbide layer consisting of crystallites of approximately 4- 15 nanometres. The diamond content of the sintered compact is expected to be approximately 99 % by volume.

Example 3

g of crushed cubic boron nitride (cBN) of average particle size 0.50 micron may be transferred into a chemical vapour deposition reactor that may be fed with a gas mixture containing BCI3-NH3-H2-Ar, at flow rates of approximately BCI3: 0.2 mI/sec; NH3: 1.0 mI/sec; H2: 0.5 mI/sec; Ar: 2 mI/sec. An opaque and semi-crystalline film of boron nitride is expected to form on the cBN particles after a dwell time of approximately 5 minutes at 950-1050 degrees centigrade. The coating is expected to be approximately 45 nm thick. The coated cBN particles may be transferred to a capsule and subjected to approximately 6 CPa and 1800-2100 degrees centigrade for approximately 30 seconds at dwell time. The sintered compact may be recovered from the capsule and high resolution scanning electron microscopy of a polished section is expected to show cBN grains connected by layers of cBN of approximately 4-12 nanometres thick. HRTEM analysis of the composite is expected to indicate that the layers have a cBN crystal structure. The cBN content of the sintered compact is expected to be approximately 95 % by volume.

Example 4

50 g of crushed cubic boron nitride (cBN) of average particle size 0.1-0.3 micron may be transferred into an atomic layer deposition reactor and coated with titanium metal using 10-30 cycles of approximately 3 seconds long each to achieve a 3-10 nanometre thick coating of titanium metal on the cBN particles. The coated cBN particles may be transferred to a capsule and subjected to approximately 6 GPa and 1800-2100 degrees centigrade for approximately 30 seconds at dwell time. The sintered compact may be recovered from the capsule and high resolution scanning electron microscopy of a polished section is expected to show cBN grains connected by layers of titanium boride and titanium nitride of approximately 2-3 nanometres thick.

The cBN content of the sintered compact is expected to be approximately 95 % by volume.

Claims

Claims 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 any one of the preceding claims, 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 any one of the preceding claims, wherein the polycrystalline superhard material comprises diamond and the inter-granular bonding layers comprise diamond.
6. A polycrystalline superhard material according to any one of claims I to 4, 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 any one of claims I to 4, wherein the polycrystalline superhard material comprises diamond and the inter-granular bonding layers comprise SiC.
8. A polycrystalline superhard material according to any one of claims I to 4, wherein the polycrystalline superhard material comprises cBN and the inter-granular bonding layers comprise cBN.
9. A polycrystalline superhard material according to any one of claims 1 to 4, 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 any one of claims 10 to 12, 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 any one of claims 10 to 13, wherein the polycrystalline superhard material comprises diamond and the bonding material is graphite or other non-diamond carbon.
15. A method according to any one of claims 10 to 13, 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 any one of claims 10 to 13, 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, wherein the polycrystalline superhard material comprises cBN and the bonding material comprises hBN.
18. A method according to any one of claims 10 to 13, 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 any one of claims 10 to 18, wherein the step of subjecting the green body to a pressure comprises subjecting the green body to a pressure of between about 5GPa or more, or 6.8GPa or more, or 7.7GPa or more, or between about 8GPa to about I 8GPa.
20. A wear element comprising a polycrystalline superhard material according to any one of claims I to 9.