BEARING ASSEMBLIES, ROLLER BEARING UNITS, RACES, METHODS OF MAKING SAME, AND APPARATUS COMPRISING SAME

Abstract

A bearing assembly includes a roller bearing unit, an inner race and an outer race. The roller bearing unit is formed of polycrystalline super-hard material having a mean mass density of at most 4.5 g/cm.sup.3 and a volume-weighted arithmetic mean thermal conductivity of at least 100 W/m.Math.K.

Claims

1. A bearing assembly comprising a roller bearing unit, an inner race and an outer race, the roller bearing unit is formed of polycrystalline super-hard material having a mean mass density of at most 4.5 g/cm.sup.3 and a volume-weighted arithmetic mean thermal conductivity of at least 100 W/m.Math.K.

2. A bearing assembly as claimed in claim 1, wherein the polycrystalline super-hard material comprises interstitial volumes between super-hard grains, the interstitial volumes including non-super-hard material or voids.

3. A bearing assembly as claimed in claim 1, wherein the super-hard material is polycrystalline diamond (PCD), or polycrystalline cubic boron nitride (PCBN), or silicon carbide-bonded diamond (SCD) material.

4. A bearing assembly as claimed in claim 1, wherein the roller bearing unit is spherical, right cylindrical, or tapered cylindrical; and the diameter of the roller bearing unit as measured on any plane perpendicular to an axis of rotation in use varies by at most 3 microns.

5. A bearing assembly as claimed in claim 1, wherein the roller bearing unit has a volume-weighted arithmetic mean coefficient of thermal expansion of at most 5.0 ppm/K throughout the volume of the roller bearing unit.

6. A bearing assembly as claimed in claim 1, wherein the roller bearing unit has a volume-weighted arithmetic mean electrical resistivity of at least 10.sup.−2 Ω.Math.cm throughout the volume of the roller bearing unit.

7. A bearing assembly as claimed in claim 1, wherein the roller bearing unit has a tensile strength of at least 1,000 MPa.

8. A bearing assembly as claimed in claim 1, wherein the roller bearing unit has a volume-weighted arithmetic mean Young's modulus of at least 450 GPa.

9. A bearing assembly as claimed in claim 1, wherein the Knoop hardness measured anywhere on the bearing surface of the roller bearing unit, or on any section surface through the roller bearing unit, is at least 25 GPa.

10. A bearing assembly as claimed in claim 1, wherein the roller bearing unit is substantially free of a cemented carbide substrate.

11. A bearing assembly as claimed in claim 1, wherein the roller bearing unit consists essentially of a mass of polycrystalline super-hard material.

12. A bearing assembly as claimed in claim 1, wherein the super-hard material comprises a plurality of directly inter-bonded diamond grains having a size distribution characteristic that the mean equivalent circle diameter is at most 10 microns, as viewed on a section through the super-hard material.

13. A bearing assembly as claimed in claim 1, wherein the roller bearing unit comprises a plurality of different super-hard materials, or different grades of the same kind or super-hard material.

14. A bearing assembly as claimed in claim 1, wherein a microstructural characteristic of the polycrystalline super-hard material comprised in the roller bearing unit varies with distance from a bearing surface.

15. A bearing assembly as claimed in claim 1, wherein the Young's modulus, or the tensile strength, or the electrical resistivity, or the thermal conductivity, or the coefficient of thermal expansion is isotropic, or uniform in magnitude throughout the volume of the roller bearing unit.

16. A bearing assembly as claimed in claim 1, wherein one or other or both of the races comprises super-hard material.

17. A bearing assembly as claimed in claim 1, comprising a plurality of roller bearing units configured such that the roller bearing units are constrained to roll between the inner and outer races in use, when the inner and outer races rotate coaxially relative to each other.

18. A bearing assembly as claimed in claim 1, wherein one or other or both of the races comprise polycrystalline super-hard material having a mean mass density of at most 4.5 g/cm.sup.3 and a volume-weighted arithmetic mean thermal conductivity of at least 100 W/m.Math.K.

19. A bearing assembly as claimed in claim 1, wherein one or other or both of the races comprises polycrystalline super-hard material including interstitial volumes between super-hard grains, the interstitial volumes including non-super-hard material or voids.

20. A bearing assembly as claimed in claim 1, wherein one or other or both of the races comprises polycrystalline diamond (PCD), or polycrystalline cubic boron nitride (PCBN), or silicon carbide-bonded diamond (SCD) material.

21. A bearing assembly as claimed in claim 1, wherein the roller bearing unit and one or other or both of the races comprise different super-hard materials, or different grades of the same type of super-hard material.

22.-23. (canceled)

24. A bearing assembly as claimed in claim 1, wherein the roller bearing unit and the races are cooperatively configured for geared inter-engagement.

25.-29. (canceled)

30. A method of making a roller bearing unit for a bearing assembly as claimed in claim 1, including: a. providing a precursor body including a precursor volume of polycrystalline super-hard material having a mean mass density of at most 4.5 g/cm.sup.3 and a volume-weighted arithmetic mean thermal conductivity of at least 100 W/m.Math.K; b. processing the precursor body to remove material such that the precursor volume is bounded by a surface defining dimensions within 10% of the corresponding dimensions of the roller bearing unit; and c. processing the precursor volume to provide the roller bearing unit.

31. A method as claimed in claim 30, wherein processing the precursor body is carried out by means of electro-discharge machining.

32.-33. (canceled)

34. A method as claimed in claim 30, including a. processing the precursor body such that the precursor volume is connected to a residual volume of the precursor body; b. processing a surface of the precursor volume such that the surface defines dimensions of the roller bearing unit; and c. processing the precursor body to remove the residual volume.

35. (canceled)

Description

[0049] Non-limiting example arrangements of roller bearing units, bearings assemblies and apparatus comprising same will be described with reference to the accompanying drawings, of which

[0050] FIG. 1 shows a schematic perspective view of an example right cylindrical roller bearing unit;

[0051] FIG. 2 shows a schematic top view of three example spherical roller bearing units (ball bearings);

[0052] FIG. 3 shows a schematic perspective view of an example roller bearing including a through-hole for cooling;

[0053] FIG. 4 shows a schematic perspective transverse cross-section view of an example Y ball bearing assembly;

[0054] FIG. 5 shows a schematic perspective transverse cross-section view of an example point angular contact roller bearing assembly;

[0055] FIG. 6 shows a schematic perspective transverse cross-section view of an example single row deep groove roller bearing assembly;

[0056] FIG. 7 shows a schematic perspective transverse cross-section view of an example single row roller bearing assembly;

[0057] FIG. 8 shows a schematic perspective transverse cross-section view of an example single row taper roller bearing assembly;

[0058] FIG. 9 shows a schematic perspective transverse cross-section view of an example needle roller machined race bearing assembly;

[0059] FIG. 10 shows a schematic perspective transverse cross-section view of an example double row angular contact roller bearing assembly;

[0060] FIG. 11 shows a schematic perspective transverse cross-section view of an example self-aligning roller bearing assembly;

[0061] FIG. 12 shows a schematic perspective transverse cross-section view of an example roller thrust bearing assembly;

[0062] FIG. 13 shows a schematic perspective transverse cross-section view of an example ball thrust bearing assembly;

[0063] FIG. 14 shows schematic perspective views of a super-hard disc (left) from which cylindrical precursor bodies have been cut, and an example precursor body (right); and

[0064] FIG. 15 shows a schematic illustration of a super-hard ball being shaped.

[0065] FIG. 1 illustrates an example right cylindrical roller bearing unit 14, FIG. 2 illustrates three example ball bearing units 24 (spherical roller bearings), and FIG. 3 illustrates an example roller bearing unit 26 provided with a diametric through-hole 27. The through-hole 27 may promote cooling of the roller bearing unit when in use, in which through-hole will be coaxial with the rolling axis. These example roller bearings 14, 24, 26 may consist essentially of PCD, or PCBN, or synthetic diamond material fabricated by means of a chemical vapour deposition process, for example.

[0066] FIG. 4 to FIG. 13 illustrate various example roller bearing assemblies, showing schematic perspective transverse cross-section views (in other words, the cross-section planes include the respective rotational axes of the roller bearing assemblies; put differently, the rotational axes lie on the respective cross-section planes). Each of the example roller bearing assemblies shown in FIG. 4 to FIG. 11 comprises at least one inner race 140, 140A, 140B and at least one outer race 130, 130A, 130B, and a plurality of roller bearing units 14, 24, 34 arranged between the inner and outer races. The example roller bearing assemblies are configured such that the inner races 140, 140A, 140B and the outer races 130, 130A, 130B are arranged coaxially, and can rotate relative to each other, the roller bearing units 14, 24, 34 rolling against the opposing race surfaces when in use.

[0067] FIG. 4 shows an example Y ball bearing assembly comprising an inner race 140, an outer race 130 and a plurality of super-hard ball bearings 24. FIG. 5 shows an example point angular contact roller bearing assembly, comprising two inner races 140A, 140B, an outer race 130 and a plurality of super-hard ball bearings 24. FIG. 6 shows an example single row deep groove roller bearing assembly, comprising a plurality of super-hard ball bearings 24. FIG. 7 shows an example single row roller bearing assembly, comprising a plurality of right cylindrical roller bearings 14. FIG. 8 shows an example single row taper roller bearing assembly, comprising a plurality of taper-cylindrical roller bearing units 34, each having a conical bearing surface. FIG. 9 shows an example needle roller machined race bearing assembly, comprising two outer races 130A, 130B. FIG. 10 and FIG. 11 show example roller bearing assemblies comprising two sets of ball bearings 24A, 24B, the sets arranged parallel and coaxially to each other; FIG. 10 shows an example double row angular contact roller bearing assembly, and FIG. 11 shows an example self-aligning roller bearing assembly.

[0068] FIG. 12 and FIG. 13 show example roller thrust bearing assemblies, in which the roller bearings 14 shown in FIG. 12 are right-cylindrical in shape, and those shown in FIG. 13 are ball bearings 24 (as used herein, ball bearings are considered to be examples of roller bearing units).

[0069] As used herein, the thermal properties of a material are measured using the laser flash analysis (LFA) method according to the ASTM E1461 standard that is suitable for the kind of material. The thermal conductivity of super-hard material is measured indirectly, by deriving the thermal conductivity from the measured thermal diffusivity, and the density and specific heat capacity of the material, via the equation λ(T)=ρ(T)×c.sub.p(T)×α(T), where T is the temperature, λ(T) is the thermal conductivity, ρ(T) is the material density, c.sub.p(T) is the specific heat capacity, and α(T) is the thermal diffusivity. As a non-limiting example, the thermal diffusivity and specific heat capacity may be measured by means of the NETSCH™ laser flash apparatus LFA 467 HyperFlash®. This apparatus was used to measure the thermal properties of PCD material from which example roller bearings were fabricated. Samples of the PCD material were prepared to the dimensions of 10 mm×10 mm×thickness of 2.2-2.4 mm.

[0070] The temperature at which the thermal properties are measured was 25° C. Each thermal property for each sample was measured five times, and the mean value was obtained. Prior to the measurement, the opposite ends of each sample were coated with graphite to enhance the emission- and absorption properties of the sample. The specific heat capacity was determined according to the standard ASTM-E 1461-2011. The density of each sample was measured at about 20-25° C. using the buoyancy flotation method.

[0071] Various example methods of fabricating PCD and PCBN bodies are known; some example methods are disclosed in WO2013092883, WO2013156536 and WO2012033930. In general, example methods of fabricating a polycrystalline super-hard material such as PCD and PCBN may include sintering an aggregation of super-hard grains, such as diamond or cBN crystallites, in the presence of a sinter catalyst material. The sinter catalyst material may promote the direct inter-bonding, or inter-growth, of the super-hard grains, and/or it may bond to the super-hard grains and connect them. For example, cobalt, iron, nickel and certain alloys including one or more of these metal elements can promote the direct inter-growth of diamond crystallites when the pressure is high enough for the diamond to be crystallographically, or thermodynamically stable, and the temperature is high enough for the metal to be molten.

[0072] An example method of making a precursor body for a PCD roller bearing unit may include sintering an aggregation of diamond grains together at an ultra-high pressure of at least about 5.5 GPa, and a temperature of at least about 1,200° C., in the presence of a source of cobalt. The aggregation of diamond grains may be provided in the form of a plurality of sheets, or as an injection moulded paste comprising diamond grains. The diamond grains may have a mean size of at least about 0.1 micron, and/or at most about 30 microns, or at most about 10 microns, and be held together by an organic binder. The sheets may be broken into pieces, or granulated, to provide a plurality of diamond-bearing granules, or flakes. Diamond-containing sheets may be made by extrusion or tape casting methods, wherein slurry comprising diamond grains and a binder material is laid onto a surface and allowed to dry. Other methods for making diamond-bearing sheets may also be used, such as described in U.S. Pat. Nos. 5,766,394 and 6,446,740. In some examples, the aggregation may comprise a mixture of diamond grains and catalyst material for diamond such as Co, Ni, Fe, Mn, which may be combined together by means of milling (e.g. ball billing), and cast into sheets using a plasticizer binder material such as PMMA and DBP.

[0073] Some example methods of making PCD material may include mixing diamond grains in the form of powder with powder material comprising cobalt, in elemental or compound form. In some examples, the source of sinter catalyst material may be deposited onto the diamond or cBN grains; for example, an oxide compound including cobalt may be deposited onto diamond grains by a chemical process, and the resulting powder including the deposited material may be treated to remove the oxygen. The amount of cobalt, for example, in the resulting combination may be about 10-30 wt. % (for example, about 20 wt. %). In various examples, the diamond or cBN powder may be provided blending a plurality of powders having substantially different grain size distributions, to provide a multi-modal mixture of powders. For example, diamond grains having a mean grain size of about 1-4 microns may be blended with diamond grains having a mean grain size of about 8-12 microns, to form blended powder having a bimodal size distribution. The diamond or cBN powder and a binder material may be compacted, for example by uniaxial or cold isostatic pressing, to form a green body. The green body may be assembled into a capsule and subjected to heat treatment to remove binder material before subjecting the capsule to an ultra-high-pressure treatment.

[0074] In some examples, a PCD disc may be cut up by wire EDM means to provide a plurality of PCD rods, which may be further processed to provide a plurality of PCD balls. The method of processing the PCD rods may include wire EDM, and/or laser ablation; and the method may include lapping and polishing the PCD balls (or cylinders) to provide roller bearing units. The lapping may comprise magnetic float lapping. Examples of float lapping processes have been disclosed by Umehara et al. (“A new apparatus for finishing large size/batch silicon nitride (Si.sub.3N.sub.4) balls for hybrid bearing applications by magnetic float polishing (MFP)”, International Journal of Machine Tools and Manufacture, vol. 46, 2006, pages 151-169); Kirtane, T. S. (“Finishing of Silicon Nitride (Si.sub.3N.sub.4) balls for advanced bearing applications by magnetic float polishing (MFP) apparatus”, Submitted to the Faculty of the Graduate College of the Oklahoma State University, December 2004); U.S. Pat. No. 7,252,576; and Jain, V. K. (“Magnetic field assisted abrasive based micro-/nano-finishing”, Journal of Materials Processing Technology, 209, 2009, pages 6022-6038). Some examples of processing example roller bearing units may include magnetic float chemo-polishing.

[0075] With reference to FIG. 14, an example method of making a precursor body 13 for a roller bearing unit 24 may include providing a disc 10 comprising PCD or PCBN material, and using a wire EDM device to cut cylindrical precursor bodies 13 out of the disc 10 (the illustration shows holes 12 in the disc 10 formed when the cylindrical precursor bodies 13 are removed).

[0076] FIG. 15 illustrates an example process for making a ball bearing unit 24 by carrying out steps A to F. In step A, a cylindrical precursor body 13 can be provided using the process described with reference to FIG. 14, for example; in step B, a wire electro-discharge (WEDM) apparatus can be used to remove material from the cylindrical precursor body 13 according to a computer-based algorithm (the position of the wire of the WEDM apparatus is indicated schematically by the vertical bar W, and the movement of the wire W is indicated by the arrows). In step C, an indexing spindle may be used to form a faceted sphere 21, still attached to a residual volume 15 of the cylindrical precursor body 13. In step D, WEDM is used with a rotating spindle to form a smoother surface on the faceted sphere 21. In step E, the faceted sphere 21 may be mounted onto a magnetic float polishing apparatus 50, co-axially with the residual volume 15 of the cylindrical element, the faceted sphere 21 held within a collet so that that the residual volume 15 can be removed by WEDM. In step F, the residual volume 15 is removed and the surface of the spherical precursor volume 23 is finished to achieve the desired diameter and sphericity to within ±2.5 microns to provide the ball bearing. In some example methods, laser ablation may be used to remove super-hard material from a sintered precursor body to provide a cylindrical or spherical roller bearing member.

[0077] In other example methods, a nearly-spherical precursor body consisting essentially of PCD or PCN can be fabricated by means of a high-pressure sintering process, and WEDM may be used to form a finished ball having the desired diameter and sphericity, within desired tolerances. The near-spherical precursor body may have a diameter of about 10-10.5 mm, and the finished ball bearing unit may have a diameter of 9.0 mm±2.5 microns, in some examples.

[0078] Some example methods of making a PCD body may include placing the mixed powders onto a substrate comprising, or consisting essentially of, cobalt-cemented tungsten carbide. The source of cobalt (and/or iron, and/or nickel) may therefore include powder mixed with the diamond powder, and/or molten cobalt or other cementing material that has migrated from the substrate and infiltrating among the diamond, or the cBN, grains during the high-pressure, high-temperature (HPHT) sinter process. The HPHT sinter process may include subjecting diamond or cBN powder grains, proximate a source of cobalt or other suitable sinter catalyst material, to a pressure of at least about 6 GPa, such as about 6.8 GPa, or about 7.8 GPa at a temperature high enough for the cobalt to melt in the presence of the diamond powder.

[0079] In some examples, diamond or cBN grains combined with a source of cobalt or other sinter catalyst material, as well as organic binder material, may be formed into spheres and sintered to provide respective spheres of PCD material having a diameter of about 4 mm, or about 10 mm, or about 12 mm. The PCD or PCBN balls may be polished to provide ball bearing units, which may be used in a turbine engine.

[0080] Some example roller bearing units may have the aspect of combining a relatively low mass density with a relatively high thermal conductivity, and/or relatively high hardness, and/or relatively low coefficient of thermal expansion, and/or relatively high tensile strength. Such roller elements may have the aspect of being particularly suitable for use in relatively high-speed rotary engines capable of operating at speeds of at least about 1,000 revolutions per minute, particularly but not exclusively for aeronautical propulsion engines. Some example roller bearing units may be capable of operating at relatively high loads, and exhibit relatively low friction, and/or relatively high mechanical shock resistance.

[0081] The use of example roller bearing assemblies may allow gas turbines to operate at substantially higher rotational speeds; for example, turbine engines such as aircraft engines comprising example super-hard bearings may have the aspect of operating at higher fan speeds, which may enhance the fuel-efficiency. Super-hard material, which may have relatively high tensile strength, may be advantageous for use in gas turbines that operate at higher rotational speeds, which may require the roller bearing units to sustain greater centripetal forces.

[0082] The effect of the bearing surfaces of both the race element and the roller elements being defined by super-hard material such as diamond may be synergistic, since the friction and the wear rate will be relatively low, which will likely enhance the operational efficiency and working life of the bearing assembly.

[0083] Some example roller bearing units may have the aspect of exhibiting relatively low rolling resistance, and require reduced energy to move in use. This may be due, at least in part, to their relatively high stiffness.

[0084] PCD may be particularly suitable for use in bearing systems, particularly but not exclusively in gas turbines, owing to its combination of relatively low density, relatively low coefficient of friction, relatively low coefficient of thermal expansion, relatively high thermal conductivity, relatively high tensile strength, relatively high abrasive wear resistance, and relatively high Young's modulus. PCBN may also have very suitable properties for use in bearings.

[0085] Example roller bearing units may exhibit a combination of increased thermal conductivity with a relatively low density (so that the mass of the bearing will be relatively reduced, all else being equal). Example roller bearings may exhibit reduced magnitude and/or frequency of heat spikes, which may be referred to as hot-spots. This may be desirable in applications where the bearing surface moves at high speed in contact with another surface, and a risk of excessive local heating of the bearing surface may arise due to friction. The risk of hot-spots may be relatively high in bearings used in gas turbines.

[0086] Some example super-hard bearing assemblies may have the aspect of requiring relatively little lubricant, or substantially no added lubricant, when in operation, even at relatively high rotation speeds, and/or relatively high operating temperature. For example, some super-hard bearings may be capable of operating at temperatures greater than about 150° C., or at least about 200° C., or at least 300° C. without the application of lubrication fluid. This may have the aspect of avoiding or reducing the need for conduits to convey lubrication fluid to the bearings, thus potentially simplifying the design of a gas turbine.

[0087] An apparatus comprising example bearing assemblies may have the aspect of requiring substantially less power to operate, all else being equal, which may be due to the relatively low mass of the roller bearing unit or units.

[0088] Some example roller bearing units, and/or races, that comprise a plurality of super-hard grains interspersed with non-super-hard material, or voids, may have the aspect of relatively high toughness and strength; this may potentially be at the expense of reduced hardness and/or thermal conductivity. While wishing not to be bound by a particular theory, the presence of interstitial volume between the super-hard grains may arrest or reduce the propagation of cracks through the material. Also, forming the roller bearing unit of a polycrystalline superhard material such as forming the entire unit of, for example PCD nor PcBN, reduces the weight of the bearing unit over conventionally used materials such as steel, which is believed to reduce the centrifugal force on the roller bearing unit in use, and also reduces the rate of frictional heating. Furthermore, as there is no interface between the polycrystalline super hard material and another material in the roller bearing unit itself, adverse effects on performance or working life which would arise in conventional units that merely have a coating of superhard material on the bulk material such as steel, due to a mismatch in thermal properties between for example the bulk of the roller bearing unit and the coating or layer of superhard material.

[0089] Certain terms and concepts as used herein are briefly explained below.

[0090] As used herein, super-hard material has a Knoop hardness of at least 25 GPa, and may have a single- or polycrystalline microstructure. For example, polycrystalline super-hard material may comprise or consist essentially of a plurality of super-hard grains (in other words, grains of super-hard material) and a plurality of volumes between the super-hard grains). Unless otherwise stated herein, an intrinsic property of polycrystalline super-hard material is measured for a representative sample of the super-hard material having a volume of at least 1 mm.sup.3.

[0091] As used herein, different types of polycrystalline super-hard materials may comprise grains of different super-hard materials, and/or different interstitial materials. A used herein, different grades of polycrystalline super-hard material of a given type may have one or more different microstructural and/or compositional characteristic. For example, different grades of PCD material may have different contents of diamond grains; and/or the size distributions of the diamond grains may be substantially different.

[0092] Polycrystalline diamond (PCD) material is a type of polycrystalline super-hard material that comprises an aggregation of diamond grains, a substantial portion of which are directly inter-bonded with each other, and in which the content of diamond is at least about 60 volume %, or at least about 80 volume % of the PCD material. Interstices between the diamond grains may be at least partly filled with solvent/catalyst material for synthetic diamond, or they may be substantially empty. As used herein, a solvent/catalyst material for synthetic diamond is capable of promoting the growth of synthetic diamond grains and or the direct inter-growth of synthetic or natural diamond grains at a temperature and pressure at which synthetic or natural diamond is crystallographically stable. Examples of solvent/catalyst materials for diamond are Fe, Ni, Co and Mn, and certain alloys including these. Bodies comprising PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains. Different grades of PCD material may comprise different contents of diamond grains, diamond grains having substantially different size distribution, and/or the composition of the metallic cementing, or interstitial material may differ.

[0093] Polycrystalline cubic boron nitride (PCBN) material is a type of polycrystalline super-hard material that comprises grains of cubic boron nitride (cBN) dispersed within a matrix comprising metal and/or ceramic material; the cBN grains may be substantially not inter-bonded with each other. Different grades of PCBN material may comprise different contents of cBN grains, and/or cBN grains having substantially different size distributions, and/or the cementing material may differ substantially.

[0094] Other types of super-hard materials may include certain composite materials comprising diamond or cBN grains held together by a matrix comprising ceramic material, such as silicon carbide (SiC), or cemented carbide material, such as Co-bonded WC material (for example, as described in U.S. Pat. No. 5,453,105 or 6,919,040). For example, certain SiC-bonded diamond materials may comprise at least about 30 volume % diamond grains dispersed in a SiC matrix (which may contain a minor amount of Si in a form other than SiC).

[0095] As used herein unless stated otherwise, physical properties are measured according to the most recent relevant ASTM (American Standard for Testing and Materials) standard, or the most recent and relevant ISO (International Organisation for Standardisation) standard if there is no suitable ASTM standard. Unless otherwise stated, a given property will be measured at a temperature of 20-25° C.

[0096] As used herein unless stated otherwise, the thermal conductivity and elastic modulus (for example, the Young's modulus) of a body comprising different materials or grades of material is calculated based on the relative volumes of the materials, as a volume-weighted arithmetic mean of the respective thermal conductivity of each constituent material or grade of materials. Polycrystalline material such as PCD, PCBN or SCD on the scale of at least 1 mm is treated as a single aggregate material having an average thermal conductivity, since the mean size of the super-hard grains and other regions within these polycrystalline materials is less than about 0.1 mm, unless otherwise stated.

[0097] As used herein, the hardness of a body refers to the Knoop indentation hardness, measured according to the ASTM E384 standard and expressed in units of pascals.

[0098] As used herein, the phrase “consists essentially of” means “consists of, apart from a non-substantial content of practically unavoidable impurities”.