EP2954082A2

EP2954082A2 - Cemented carbide material and method of making same

Info

Publication number: EP2954082A2
Application number: EP14703394.8A
Authority: EP
Inventors: Igor Yurievich KONYASHIN; Bernd Heinrich Ries; Frank Friedrich Lachmann
Original assignee: Element Six GmbH
Current assignee: Element Six GmbH
Priority date: 2013-02-11
Filing date: 2014-02-10
Publication date: 2015-12-16
Anticipated expiration: 2034-02-10
Also published as: GB201402248D0; JP6275750B2; EP2954082B1; WO2014122306A2; US20210222273A1; WO2014122306A3; US20150376744A1; CN105074029B; CN105074029A; GB2512983A; GB201302345D0; GB2512983B; JP2016513177A; US20190368011A1

Abstract

A cemented carbide material comprises WC, between around 3 to around 10 wt.% Co and between around 0.5 to around 8 wt.% Re. The equivalent total carbon (ETC) content of the cemented carbide material with respect to WC is between around 6.3 wt.% to around 6.9 wt.% and the cemented carbide material is substantially free of eta-phase and free carbon. There is also disclosed a method of producing such a material and use of such a material.

Description

CEMENTED CARBIDE MATERIAL AND METHOD OF MAKING SAME

Field

This disclosure is related to a cemented carbide material such as for use in high-pressure components for synthesis of diamond or c-BN or fabrication of poly-crystalline diamond or c-BN and a method of making same.

Background

It is well known that cemented carbides employed for high-pressure high-temperature (HPHT) components used for diamond synthesis and production of polycrystalline diamond (PCD), including anvils and dies, are subjected to high pressures, temperatures and loads. Such unfavorable conditions lead to their deformation and, if the deformation exceeds a certain level, the HPHT components fail. In this respect it is very important to have a cemented carbide material with a high level of Young's modulus to reduce the deformation at high pressures and consequently improve the deformation resistance and lifetime of the HPHT components.

There is therefore a need for a cemented carbide material for use in the fabrication of high- pressure high-temperature components having improved resistance to deformation as well as high fracture toughness and strength.

Summary

Viewed from a first aspect there is provided a cemented carbide material comprising WC, Co and Re, wherein: the cemented carbide material comprises between around 3 to around 10 wt.% Co and between around 0.5 to around 8 wt.% Re;

the equivalent total carbon (ETC) content of the cemented carbide material with respect to WC being between around 6.3 wt.% to around 6.9 wt.%

the cemented carbide material being substantially free of eta-phase and free carbon.

Viewed from a second aspect there is provided a polycrystalline superhard construction comprising: a substrate comprising the cemented carbide material defined above; and a body of polycrystalline superhard material bonded to the substrate along an interface.

Viewed from a third aspect there is provided a cutter comprising a substrate comprising the cemented carbide material defined above bonded to a body of polycrystalline superhard material adapted for a rotary drill bit for boring into the earth.

Viewed from a fourth aspect there is provided a PCD element for a rotary shear bit for boring into the earth, for a percussion drill bit or for a pick for mining or asphalt degradation, comprising a cutter element comprising a body of superhard polycrystalline material bonded to a body of cemented carbide material as defined above.

Viewed from a fifth aspect a drill bit or a component of a drill bit for boring into the earth, comprising a PCD element as defined above.

Viewed from a sixth aspect there is provided a method of producing the cemented carbide material defined above, the method comprising: milling a cemented carbide mixture containing WC and carbon with Re, Co, Ni and/or Fe and optionally grain growth inhibitors comprising one or more of V, Cr, Ta, Ti, Mo, Zr, Nb and Hf or a carbide thereof; pressing the cemented carbide article from the mixture; sintering the article at a temperature of above around 1450°C in vacuum for between around 1 to 10 minutes and a pressure of Ar (HIP) for around 5 to 120 minutes; and cooling the article from sintering the temperature to approximately 1300 degrees Centigrade (°C).

Viewed from a seventh aspect there is provided a method of recycling the cemented carbide material defined above, the method comprising melting the carbide material in a protective atmosphere with liquid Zn, evaporating the Zn to form a resultant product; and milling the resulting product to recover Re from the product.

Viewed from an eighth aspect there is provided a method of recycling the cemented carbide material defined above, the method comprising subjecting the cemented carbide material to an acid leaching mixture to remove the binder phase from the cemented carbide material; and chemically recovering Co and Re from the removed binder phase.

Viewed from a ninth aspect there is provided a method of recycling the cemented carbide material defined above, the method comprising oxidation of the cemented carbide material to dissolve the carbide, Re and Co, and recovering the Re.

Viewed from a tenth aspect there is provided a use of a cemented carbide material in a high- pressure component for synthesis of diamond or c-BN, or in fabrication of polycrystalline diamond or c-BN operating at a pressure of above 5 GPa and a temperature of above 1 100°C, wherein the cemented carbide material comprises: a carbide of one or more metals in form of the second carbide phase, or dissolved in a binder phase in the material, said one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta; between around 0.5 to around 8 wt.% Re and between around 3 to around 10 wt.% Co; the equivalent total carbon (ETC) content of the cemented carbide material with respect to WC being between around 6.3 wt.% to around 6.9 wt.%

Brief description of the drawings

Embodiments will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 is an SEM image of a cemented carbide material according to a first example and comprising WC-Co-Re;

Figure 2 is an EBSD image of the WC-Co-Re cemented carbide material of Figure 1 ; and

Figure 3 is an EBSD image showing the microstructure of conventional WC-Co cemented carbide material.

Detailed Description It is well known that the equivalent total carbon (ETC) content with respect to WC of conventional WC-Co materials lies between roughly 6.0 and 6.3 wt.%. [see e.g. "Exner H., Gurland J. A review of parameters influencing some mechanical properties of tungsten carbide- cobalt alloy. Powder Met., 13 (1970) 13-31 )"; and I. Konyashin, S. Hlawatschek , B. Ries, F. Lachmann, T. Weirich, F. Dorn, A. Sologubenko on the "Mechanism of WC Coarsening in WC- Co Hardmetals with Various Carbon Contents", International Journal of Refractory Metals and Hard Materials, 27 (2009) 234-243"]. When the carbon content is lower or higher than that of this range, additional phases (such as eta-phase or free carbon) appear in the carbide microstructure leading to a significant decrease in the mechanical properties of WC-Co materials, such as compressive strength, transverse rupture strength, and fracture toughness.

It has now been surprisingly appreciated that if WC-Co-Re cemented carbides have a significantly increased carbon content, which corresponds to the equivalent total carbon (ETC) content with respect to WC of between 6.3 wt.% and 6.9 wt.%, their mechanical properties such as compressive strength, transverse rupture strength, hardness, fracture toughness and hot hardness may be dramatically improved.

Whilst not wishing to be bound by theory, a possible reason for this may be the presence of residual compressive stresses in the binder phase of the WC-Co-Re cemented carbides in such materials. According to numerous publications on residual stresses in WC-Co cemented carbides, the binder phase in WC-Co is always under high residual tensile stresses resulting in decreased combinations of hardness and fracture toughness of conventional WC-Co materials [see for example the publication by Mari D, Clausen B, Bourke M A M, Buss K. entitled "Measurement of residual thermal stress in WC-Co by neutron diffraction", Int. J. Refractory Met. Hard Mater., 2009; 27: 282-287", the publication by Krawitz A D, Venter A M, Drake E F, Luyckx S B, Clausen B entitled "Phase response in WC-Ni to cyclic compressive loading and its relation to roughness", Int. J. Refractory Met. Hard Mater., 2009; 27: 313-316", and the publication by Coats D I, Krawitz A D entitled "Effect of particle size on thermal residual stress in WC-Co composites", Mater. Sci. Engin., 2003; A359:338-342"].

As used herein, a "superhard material" is a material having a Vickers hardness of at least about 25GPa. Diamond and cubic boron nitride (cBN) material are examples of superhard materials. As used herein, a "superhard construction" means a construction comprising polycrystalline superhard material or superhard composite material, or comprising polycrystalline superhard material and superhard composite material bonded to a cemented carbide substrate.

As used herein, polycrystalline diamond (PCD) is a PCS material comprising a mass 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 80 volume percent of the material. In one embodiment of PCD material, interstices between the diamond gains may be at least partly filled with a binder material comprising a catalyst for diamond. As used herein, "interstices" or "interstitial regions" are regions between the diamond grains of PCD material. In embodiments of PCD material, interstices or interstitial regions may be substantially or partially filled with a material other than diamond, or they may be substantially empty. Embodiments of 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.

As used herein, polycrystalline cubic boron nitride (PCBN) material is a PCS material comprising a mass of cBN grains dispersed within a wear resistant matrix, which may comprise ceramic or metal material, or both, and in which the content of cBN is at least about 50 volume percent of the material. In some embodiments of PCBN material, the content of cBN grains is at least about 60 volume percent, at least about 70 volume percent or at least about 80 volume percent. Embodiments of superhard material may comprise grains of superhard materials dispersed within a hard matrix, wherein the hard matrix preferably comprises ceramic material as a major component, the ceramic material preferably being selected from silicon carbide, titanium nitride and titanium carbo-nitride.

With reference to Figure 1 and Figure 2, a cemented carbide material comprises a mass of grains of a hard material comprising a carbide phase and interstices between the hard grains which are filled with a binder material which constitutes the binder phase. In the embodiment shown in Figure 1 , the carbide phase is WC and the binder phase comprises an alloy of Co and Re with some W and C dissolved in it.

Figure 3 shows, for comparison, a conventional cemented carbide material comprising WC as the carbide phase and Co as the binder phase. In some embodiments, the cemented carbide material further comprises a carbide of one or more metals in the form of a second carbide phase or dissolved in the binder phase, the one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta. The cemented carbide material is substantially free of eta-phase and free carbon.

In some embodiments, the cemented carbide material comprises between around 0.5 to around 8 wt% Re.

In some embodiments, the cemented carbide material comprises between around 3 to around 10 wt.% Co.

In other embodiments, the cemented carbide material comprises between around 0.5 to around 6 wt.% Re.

The WC in the cemented carbide material may, for example, have a mean grain size below around 0.6 microns.

Furthermore, in some embodiments, the equivalent total carbon (ETC) content with respect to WC lies between around 6.3 wt% to around 6.9 wt%.

The magnetic properties of the cemented carbide material may be related to important structural and compositional characteristics and is understood to be an indication of the carbon content in the cemented carbide material. The most common technique for measuring the carbon content in cemented carbides is indirectly, by measuring the concentration of tungsten dissolved in the binder to which it is indirectly proportional. The higher the content of carbon dissolved in the binder the lower the concentration of tungsten dissolved in the binder. The magnetic saturation 4πσ or magnetic moment σ of a hard metal, of which cemented tungsten carbide is an example, is defined as the magnetic moment or magnetic saturation per unit weight. The magnetic moment, σ, of pure Co is 16.1 micro-Tesla times cubic metre per kilogram ^T.m³/kg), and the induction of saturation, also referred to as the magnetic saturation, 4πσ, of pure Co is 201.9 μΤ.ΓΤι³^ . The tungsten content within the binder may be determined from a measurement of the magnetic moment, σ, or magnetic saturation, M_s = 4πσ, these values having an inverse relationship with the tungsten content (Roebuck (1996), "Magnetic moment (saturation) measurements on cemented carbide materials", Int. J. Refractory Met, Vol. 14, pp. 419-424.). The following formula may be used to relate magnetic saturation, Ms, to the concentrations of W and C in the binder:

Ms oc [C]/[W] x wt.% Co x 201.9 in units of μΤ. ΠΊ³/Ι¾

Some embodiments of the cemented carbide material have an associated magnetic saturation of at least around 40 percent to around 80 percent of the magnetic saturation of nominally pure Co.

The mean grain size of carbide grains, such as WC grains, may be determined by examination of micrographs obtained using a scanning electron microscope (SEM) or light microscopy images of metallurgically prepared cross-sections of a cemented carbide material body, applying the mean linear intercept technique, for example. Alternatively, the mean size of the WC grains may be estimated indirectly by measuring the magnetic coercivity of the cemented carbide material, which indicates the mean free path of Co intermediate the grains, from which the WC grain size may be calculated using a simple formula well known in the art. This formula quantifies the inverse relationship between magnetic coercivity of a Co-cemented WC cemented carbide material and the Co mean free path, and consequently the mean WC grain size. Magnetic coercivity has an inverse relationship with MFP.

As used herein, the "mean free path" (MFP) of a composite material such as cemented carbide is a measure of the mean distance between the aggregate carbide grains cemented within the binder material. The mean free path characteristic of a cemented carbide material may be measured using a micrograph of a polished section of the material. For example, the micrograph may have a magnification of about 1500x. The MFP may be determined by measuring the distance between each intersection of a line and a grain boundary on a uniform grid. The matrix line segments, Lm, are summed and the grain line segments, Lg, are summed. The mean matrix segment length using both axes is the "mean free path". Mixtures of multiple distributions of tungsten carbide particle sizes may result in a wide distribution of MFP values for the same matrix content.

As used herein, the grain sizes are expressed in terms of Equivalent Circle Diameter (ECD) according to the ISO FDIS 13067 standard. The ECD is obtained by measuring of the area A of each grain exposed at the polished surface and calculating the diameter of a circle that would have the same area A, according to the equation ECD = (4A/ ττ) ² (See section 3.3.2 of ISO FDIS 13067 "Microbeam analysis— Electron Backscatter Diffraction - Measurement of average grain size.", International Standards Organisation Geneva, Switzerland, 201 1 ).

In some embodiments, the carbide phase of the cemented carbide material is formed of carbide grains having a mean grain size of at least around 0.1 μηι to at most around 10 μηι and the cemented carbide material may have an associated magnetic coercive force varying from around 2kA/m to around 70 kA/m.

In some embodiments, the carbide phase comprises WC and the cemented carbide material has a coercive force He in kA/m as a function of the WC mean grain size D_wc in μηι determined on the basis of EBSD images of the carbide microstructure equal to or less than values given by the equation:

Hc = 10 x D_wc -°-⁶²

In some embodiments, the carbide phase comprises WC and the binder phase comprises Co and Re.

The binder phase of the cemented carbide material may, for example, be a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni. In some embodiments, the binder phase comprises at least about 0.1 weight percent to at most about 5 weight percent of one or more of V, Cr, Ta, Ti, Mo, Zr, Nb and Hf in solid solution and/or in the form of carbide compounds. In some other embodiments, the material comprises at least about 0.01 weight percent and at most about 2 weight percent of one or more of Ru, Rh, Pd, Os, Ir and Pt.

The cemented carbide has an associated hardness and, in some embodiments, the hardness decrease at 300°C is at most 20%, or, in some other embodiments, is at most 17%. Hardness measurements were carried out according to the DIN ISO 3878 on metallurgical cross-sections at a load of 30 kgf at room temperature as well as at 300°C, 500°C and 800°C in an Ar atmosphere. After achieving the elevated temperatures the cross-section was annealed for 10 min, after which a Vickers indentation was made under the load of 30 kgf and the load was applied for 15 sec. The hardness values of both a conventional cemented carbide material containing a Co binder and an embodiment of cemented carbide material containing the Co-Re binder were measured, and a decrease of hardness at the elevated temperatures compared to that at room temperature was calculated for both the conventional material and embodiment material.

The cemented carbide material may, for example, have a hardness decrease at 500°C of at most 30% or, in some other embodiments, at most 27%.

The hardness-toughness coefficient may be calculated by multiplying the Vickers hardness in GPa and indentation fracture toughness in MPa m ², and, in some embodiments, this is above 150. In some emboidments, the cemented carbide material has a Vickers hardness

In some embodiments, the binder phase of the cemented carbide material has one or more residual compressive stresses and these may, for example, be between around -5 MPa to around 100 MPa.

An embodiment of a cemented carbide material may be made by a method including milling a cemented carbide mixture containing carbides with Re, Co, Ni and/or Fe and optionally grain growth inhibitors including V, Cr, Ta, Ti, Mo, Zr,, Nb and Hf or their carbides and then pressing a cemented carbide article from the mixture. The article is then sintered at temperatures of above 1450°C in vacuum for 1 to 10 min and afterwards under pressure of Ar (HIP) for 5 to 120 min. The article is then cooled from the sintering temperatures to approximately 1300 degrees Centigrade (°C) in an atmosphere comprising inert gases, nitrogen, hydrogen or a mixture thereof, or in a vacuum, at a cooling rate of approximately 0.2 to 2 degrees per minute.

Some embodiments are now described in more detail with reference to the following example below, which is not intended to be limiting.

Example

Tungsten carbide powder, wherein the WC grains had an average grain size of about 0.6 μηι with carbon content of 6.13 wt.%, was milled with 5.5%Re powder and 3.7%Co powder. The Co grains had an average grain size of about 1 μηι. The powder mixture was produced by milling the powders together for 24 hours using a ball mill in a milling medium comprising hexane with 2 wt.% paraffin wax, and using a powder-to-ball ratio of 1 :6. After milling 0.35 wt.% carbon black was added and additional milling was performed for 1 hr resulting in the fact that the equivalent total carbon (ETC) content with respect to WC of the mixture was equal to 6.51 wt.%. After drying the mixture, green bodies were pressed and sintered at 1540°C for 60 min (30 min vacuum + 30 min HIP in Ar at a pressure of 50 Bar). After the sintering at 1540°C the bodies were cooled down to 1300°C at a rate of 0.5 degrees per min and afterwards at an uncontrolled rate down to room temperature. The carbon content was measured on the sintered samples after their crushing by hand with the aid of of the LECO WC600 instrument and determined to be equal to 5.85 wt.% providing evidence that the equivalent total carbon (ETC) content with respect to WC is equal to 6.44 wt%.

A control batch of conventional WC-Co cemented carbides without Re was made from the same WC powder batch and 6 wt.% Co, which corresponds to the same volume percentage of binder as in the WC-Co-Re material, without adding carbon black. The batch was milled in the same way as the WC-Co-Re carbide and sintered at 1440°C for 1 hr including 30 sintering vacuum and 30 min sintering under pressure (HIP). The carbon content was measured on sintered samples in the same way as for the WC-Co-Re cemented carbides and found to be equal to 5.77 wt.% providing evidence that the equivalent total carbon (ETC) content with respect to WC is equal to 6.13 wt%.

Metallurgical cross-sections of the WC-Co-Re and WC-Co cemented carbides were made and examined by optical microscopy and SEM. The hardness (HV20), indentation fracture toughness (Kic), transverse rupture strength (TRS), compressive strength and Young's modulus as well as coercive force and magnetic moment (saturation) of the sintered bodies were examined.

The WC mean grain size was measured on the basis of the EBSD image of the cross-sections according to the procedure described in: K.P. Mingard, B. Roebuck a, E.G. Bennett , M.G. Gee, H. Nordenstrom, G. Sweetman, P. Chan . Comparison of EBSD and conventional methods of grain size measurement of hard metals. Int. Journal of Refractory Metals & Hard Materials 27 (2009) 213-223.

Figures 1 and 2 show SEM and EBSD images respectively of the WC-Co-Re cemented carbide formed according to Example 1 , and Figure 3 shows the microstructure of the conventional WC- Co cemented carbides without Re and having the Equivalent Total Carbon content with respect to WC of 6.13 wt.%. The WC-Co-Re carbide shown in Figure 1 and Figure 2 has a WC mean grain size of 0.44 μηι. It will be seen that there is neither eta-phase nor free carbon nor porosity in the microstructure of both carbide materials shown in Figures 1 and 2. Table 1 shows the grain size distribution in the microstructure of the WC-Co-Re cemented carbide shown in Figures 1 and 2.

Table 1

Grain size distribution in the microstructure of the WC-Co-Re cemented carbide.

The magnetic moment of the WC-Co-Re carbide material of Figure 1 and Figure 2 was equal to 4.7 Gcm³/g, which is 64% of the theoretical value for cemented carbide with 3.7 % of nominally pure Co providing evidence for its specific magnetic saturation in per cent (SMS). The coercive force of the WC-Co-Re material was determined to be 284 Oe. Its mechanical properties were determined to be HV20=1860 or 18.6 GPa, K_1C= 10.5 MPa m^½, and TRS=3700 MPa. The hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m ² was therefore equal to 195. The compressive strength of the WC-Co-Re cemented carbide was determined to be 6020 MPa and its Young's modules to be equal to 712 GPa. Its hot hardness was found to be equal to 16.9 GPa at 300°C and 14.9 GPa at 500°C providing evidence that the hardness decrease at the elevated temperatures was about 9.1 % and 19.8% correspondingly. The compressive strength almost did not change when increasing the temperatures from room temperature to 300°C and 500°C.

The residual stress in the Co-Re binder phase of the WC-Co-Re cemented carbide was measured using a Bruker D8 Discover d iff racto meter using the Cu-Κα radiation. This wavelength of X-ray typically obtained diffraction information from a depth of around 5 μηι. The diffracted beam was collected using a Braun Position Sensivite Detector with a bin size of 0.01059°. The residual stress measurement was performed by use of the Co (21 1 ) peak at an angle of 146.6° using a step size of 0.01059° and a count time of 10 sec. per step. The residual stress measurements were performed using the standard iso. inclination είη²ψ technique in accordance with the ref. "Fitzpatrick M, Fry T, Holdway P, et al. NPL Good Practice Guide No. 52: Determination of Residual Stresses by X-ray Diffraction - Issue 2. September 2005".

Two measurements of the WC-Co-Re cemented carbide were made which provided data with the compressive stress being -1 1 MPa in the Phi = 0 direction and -8MPa in the Phi =90 direction for the first measurement; and -9MPa in the Phi = 0 direction and -31 MPa in the Phi =90 direction for the second measurement. Therefore, in all the cases the binder phase of the WC- Co-Re materials was under residual compressive stresses.

The magnetic moment of the conventional WC-6%Co carbide material, having the same volume proportion of the binder phase as the WC-Co-Re cemented carbide was found to be equal to 9.2 Gcm³/g , which is 95.2% of the theoretical value for the cemented carbide with 6% nominally pure Co, the coercive force was 270 Oe, HV20=1610 or 16.1 GPa, K _1C= 9.5 MPa m ^½, TRS=2900 MPa, compressive strength was 5200 GPa and Young's modulus of 640 GPa. Its WC mean grain size was determined to be equal to 0.59 μηι. Its hot hardness was found to be equal to 12.1 GPa at 300°C and 8.1 GPa at 500°C providing evidence that the hardness decrease was about 25% and 49% correspondingly.

Young's modulus is a type of elastic modulus and is a measure of the uni-axial strain in response to a uni-axial stress, within the range of stress for which the material behaves elastically. A method of measuring the Young's modulus E is by means of measuring the transverse and longitudinal components of the speed of sound through the material using ultrasonic waves. In particular, a preferred method of measuring the Young's modulus E is by means of measuring the transverse and longitudinal components of the speed of sound through the material, according to the equation E = 2p.C_T ²(1 + υ), where v = (1 - 2 (C_TI C_L)²) I (2 - 2 (C_T I C_L)²), C_l and C_T are respectively the measured longitudinal and transverse speeds of sound through it and p is the density of the material. The longitudinal and transverse speeds of sound may be measured using ultrasonic waves, as is well known in the art. Where a material is a composite of different materials, the mean Young's modulus may be estimated by means of one of three formulas, namely the harmonic, geometric and rule of mixtures formulas as follows: E = 1 / ( fi / Έ, + f₂ / E₂) ); E = Ei ^f1 + Ei ^f2; and E = f, E, + f₂ E₂; in which the different materials are divided into two portions with respective volume fractions of f₁ and f₂, which sum to one.

The cemented carbide material of one or more embodiments may find particular application in use in high-pressure components for synthesis of diamond or c-BN, or in fabrication of poly- crystalline diamond or c-BN operating at pressures of above 5 GPa and temperatures of above 1 100°C.

In such applications, PCD composite compact elements may comprise a PCD structure bonded along an interface to an embodiment of a cemented carbide substrate comprising particles of a metal carbide and the binder material described above.

An embodiment of a PCD composite compact element may be made by a method including providing the cemented carbide substrate, contacting an aggregated, substantially unbonded mass of diamond particles against a surface of the substrate to form an pre-sinter assembly, encapsulating the pre-sinter assembly in a capsule for an ultra-high pressure furnace and subjecting the pre-sinter assembly to a pressure of at least about 5.5 GPa and a temperature of at least about 1 ,250 degrees centigrade, and sintering the diamond particles to form a PCD composite compact element comprising a PCD structure integrally formed on and joined to the cemented carbide substrate. In some embodiments of the invention, the pre-sinter assembly may be subjected to a pressure of at least about 6 GPa, at least about 6.5 GPa, at least about 7 GPa or even at least about 7.5 GPa.

The hardness of cemented tungsten carbide substrate may be enhanced by subjecting the substrate to an ultra-high pressure and high temperature, particularly at a pressure and temperature at which diamond is thermodynamically stable. The magnitude of the enhancement of the hardness may depend on the pressure and temperature conditions. In particular, the hardness enhancement may increase the higher the pressure. Whilst not wishing to be bound by a particular theory, this is considered to be related to the Co drift from the substrate into the PCD during press sintering, as the extent of the hardness increase is directly dependent on the decrease of Co content in the substrate. In some embodiments, as described above, the cemented carbide material forming the substrate may comprise between around 2 to around 9 wt.% Re, and around 3 to around 9 wt.%Co, with the remainder being WC.

The working temperature on the surface of the high-pressure components may be at least around 200°C and at most around 800°C.

In connection with the present invention, it has now been surprising found out that if the cemented carbide contains cobalt (Co) and rhenium (Re) and the proportion of Re and Co lies in a certain range it may be possible to improve significantly the Young's modulus of the cemented carbide material. At the same time it may be possible to improve the cemented carbide hot hardness at temperatures dramatically of up to 800°C. As a result, it may be possible to employ embodiments of the WC-Co-Re cemented carbide materials as HPHT components.

Furthermore, it may be possible to recycle used embodiments of cemented carbide materials. This has clear environmental and economic benefits. The recycling procedure may comprise melting the cemented carbide material in a protective atmosphere with liquid Zn with consequent evaporation of Zn from the mixture, and milling the resulting product.

Alternatively, the cemented carbide material may be subjected to an acid leaching treatment to remove the binder phase of the cemented carbide article and chemically recover the Co and Re.

A further method of recycling the cemented carbide material may comprise oxidation of the cemented carbides articles with consequent dissolution of carbides, Re and Co and their recovery.

While various embodiments have been described with reference to the example, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof and that these examples are not intended to limit the particular embodiments disclosed.

Claims

1. A cemented carbide material comprising WC, Co and Re, wherein: the cemented carbide material comprises between around 3 to around 10 wt.% Co and between around 0.5 to around 8 wt.% Re;

2. The cemented carbide material of claim 1 , wherein the cemented carbide material comprises between around 0.5 to around 6 wt% Re.

3. The cemented carbide material of claim 1 or 2, wherein the WC in the material has a mean grain size less than around 0.6 μηι.

4. The cemented carbide material of any one of the preceding claims, wherein the cemented carbide material has a magnetic saturation of at least around 40 percent to around 80 percent of the magnetic saturation of nominally pure Co.

5. The cemented carbide material of any one of the preceding claims, wherein the carbide phase is formed of carbide grains having a mean grain size of at least around 0.1 μηι to at most around 10 μηι.

6. The cemented carbide material of any one of the preceding claims, wherein the cemented carbide material has an associated magnetic coercive force varying from around 2kA/m to around 70 kA/m.

7. The cemented carbide material of any one of the preceding claims, further comprising a carbide of one or more metals in form of the second carbide phase, or dissolved in a binder phase in the material, said one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta.

8. The cemented carbide material of any one of the preceding claims, wherein the material comprises a binder phase having one or more residual compressive stresses.

9. The cemented carbide material of claim 8, wherein the binder phase has one or more residual compressive stresses of between around -5 MPa to around 100 MPa.

10. The cemented carbide material of any one of claims 8 or 9, wherein the binder phase comprises a binder material comprising Co, Re, W and C.

1 1 . The cemented carbide material of any one of claims 8 or 9, wherein the binder phase comprises a binder material, the binder material comprising a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni.

12. The cemented carbide material as claimed in any one of the preceding claims, wherein the carbide phase comprises WC; and the cemented carbide material has a coercive force He in kA/m as a function of the WC mean grain size D_wc in μηι determined on the basis of EBSD images of the carbide microstructure equal to or less than values given by the equation:

Hc = 10 x D_wc -°-⁶²

13. The cemented carbide material as claimed in any one of the preceding claims, wherein the material has a compression strength above around 5500 MPa at room temperature and at an elevated temperature of up to around 500°C.

14. The cemented carbide material of claim 13, wherein the material has a Vickers hardness, and the hardness decrease at 300°C is at most around 12%.

15. The cemented carbide material as claimed in any one of the preceding claims, wherein the material has a Vickers hardness, and wherein the hardness decrease at 500°C is at most around 21 %.

16. The cemented carbide material as claimed in any one of the preceding claims, wherein the Young's Modulus of said material is above around 700 GPa.

17. The cemented carbide material as claimed in any one of the preceding claims, wherein the hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m ² is above around 190.

18. The cemented carbide material as claimed in any one of the preceding claims, comprising a binder phase having a binder material comprising at least about 0.1 weight percent to at most about 5 weight percent of one or more of V, Cr, Ta, Ti, Mo, Zr, Nb and Hf in solid solution and/or in the form of carbide compounds.

19. The cemented carbide material as claimed in any one of the preceding claims, wherein the material comprises at least about 0.01 weight percent and at most about 2 weight percent of one or more of Ru, Rh, Pd, Os, Ir and Pt

20. A polycrystalline superhard construction comprising: a substrate comprising the cemented carbide material of any one of claims 1 to

19; and a body of polycrystalline superhard material bonded to the substrate along an interface.

21 . The polycrystalline superhard construction of claim 20, wherein the body of polycrystalline superhard material comprises polycrystalline diamond (PCD) material.

22. The polycrystalline superhard construction of claim 20, wherein the body of polycrystalline superhard material comprises PCBN.

23. A cutter comprising a substrate comprising the cemented carbide material of any one of claims 1 to 19 bonded to a body of polycrystalline superhard material adapted for a rotary drill bit for boring into the earth.

24. A PCD element for a rotary shear bit for boring into the earth, for a percussion drill bit or for a pick for mining or asphalt degradation, comprising a cutter element comprising a body of superhard polycrystalline material bonded to a body of cemented carbide material as claimed in any one of claims 1 to 19.

25. A drill bit or a component of a drill bit for boring into the earth, comprising a PCD element as claimed in claim 24.

26. A method of producing the cemented carbide material of any one of claims 1 to 19, the method comprising: milling a cemented carbide mixture containing WC and carbon with Re, Co, Ni and/or Fe and optionally grain growth inhibitors comprising one or more of V, Cr, Ta, Ti, Mo, Zr, Nb and Hf or a carbide thereof;

pressing the cemented carbide article from the mixture;

sintering the article at a temperature of above around 1450°C in vacuum for between around 1 to 10 minutes and a pressure of Ar (HIP) for around 5 to 120 minutes; and cooling the article from sintering the temperature to approximately 1300 degrees Centigrade (°C) .

27. The method of claim 26, wherein the step of cooling the article comprises cooling the article in an atmosphere comprising one or more of an inert gas, nitrogen, hydrogen or a mixture thereof, at a cooling rate of approximately 0.2 to 2 degrees per minute.

28. The method of claim 26, wherein the step of cooling the article comprises cooling the article in a vacuum at a cooling rate of approximately 0.2 to 2 degrees per minute.

29. The method of any one of claims 26 to 28, wherein the step of milling the cemented carbide mixture comprises milling the one or more carbides with between around 0.5 to around 8 wt % Re to form the cemented carbide material comprising between around 0.5 to around 8 wt% Re.

30. A method of recycling the cemented carbide material of any one of claims 1 to 19, the method comprising melting the carbide material in a protective atmosphere with liquid Zn, evaporating the Zn to form a resultant product; and milling the resulting product to recover Re from the product.

31 . A method of recycling the cemented carbide material of any one of claims 1 to 19, the method comprising subjecting the cemented carbide material to an acid leaching mixture to remove the binder phase from the cemented carbide material; and chemically recovering Co and Re from the removed binder phase.

32. A method of recycling the cemented carbide material of any one of claims 1 to 19, the method comprising oxidation of the cemented carbide material to dissolve the carbide, Re and Co, and recovering the Re.

33. Use of a cemented carbide material in a high-pressure component for synthesis of diamond or c-BN, or in fabrication of polycrystalline diamond or c-BN operating at a pressure of above 5 GPa and a temperature of above 1 100°C, wherein the cemented carbide material comprises: a carbide of one or more metals in form of the second carbide phase, or dissolved in a binder phase in the material, said one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta; between around 0.5 to around 8 wt.% Re and between around 3 to around 10 wt.% Co; the equivalent total carbon (ETC) content of the cemented carbide material with respect to WC being between around 6.3 wt.% to around 6.9 wt.%

34. Use of the cemented carbide material as claimed in claim 33, wherein the cemented carbide material comprises between around 0.5 to around 6 wt.% Re.

35. Use of the cemented carbide material as claimed in any one of claims 33 or 34, wherein the WC in the material has a mean grain size less than around 0.6 μηι.

36. Use of the cemented carbide material as claimed in any one of claims 33 to 35, wherein the cemented carbide material has a magnetic saturation of at least around 40 percent to around 80 percent of the magnetic saturation of nominally pure Co.

37. Use of the cemented carbide material as claimed in any one of claims 33 to 36, wherein the carbide phase is formed of carbide grains having a mean grain size of at least around 0.1 μηι to at most around 10 μηι.

38. Use of the cemented carbide material as claimed in any one of claims 33 to 37, wherein the cemented carbide material has an associated magnetic coercive force varying from around 2kA/m to around 70 kA/m.

39. Use of the cemented carbide material as claimed in any one of claims 33 to 38, wherein the carbide phase comprises WC.

40. Use of the cemented carbide material as claimed in any one of claims 33 to 39, the cemented carbide material comprising a binder phase having a binder material comprising Co, Re, W and C.

41 . Use of the cemented carbide material as claimed in any one of claims 33 to 39, the cemented carbide material comprising a binder phase having a binder material, the binder material comprising a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni.

42. Use of the cemented carbide material as claimed in any one of claims 33 to 41 , wherein the carbide phase comprises WC; and the cemented carbide material has a coercive force He in kA/m as a function of the WC mean grain size D_wc in μηι determined on the basis of EBSD images of the carbide microstructure equal to or less than values given by the equation:

Hc = 10 x D_wc -°-⁶²

43. Use of the cemented carbide material as claimed in any one of claims 33 to 42, wherein the material has a Vickers hardness, and wherein the hardness decrease at 300°C compared to that at room temperature is at most 20%.

44. Use of the cemented carbide material as claimed in claim 43, wherein the hardness decrease at 300°C is at most 17%.

45. Use of the cemented carbide material as claimed in any one of claims 33 to 44, wherein the material has a Vickers hardness, and wherein the hardness decrease at 500°C is at most 30%.

46. Use of the cemented carbide material as claimed in claim 45, wherein the hardness decrease at 500°C is at most 27%.

47. Use of the cemented carbide material as claimed in any one of claims 33 to 46, wherein the hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m ² is above 150.

48. Use of the cemented carbide material as claimed in any one of claims 33 to 47, wherein the material comprises a binder phase having a binder material comprising at least about 0.1 weight percent to at most about 5 weight percent of one or more of V, Cr, Ta, Ti, Mo, Zr, Nb and Hf in solid solution and/or in the form of carbide compounds.

49. Use of the cemented carbide material as claimed in any one of claims 33 to 48, wherein the material comprises at least about 0.01 weight percent and at most about 2 weight percent of one or more of Ru, Rh, Pd, Os, Ir and Pt.

50. A cemented carbide material substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings.

51 . A method of producing the cemented carbide material substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings.