CEMENTED CARBIDE MATERIAL, A POLYCRYSTALLINE DIAMOND CONSTRUCTION INCLUDING CEMENTED CARBIDE MATERIAL AND METHOD OF MAKING SAME

Abstract

A cemented carbide material includes WC, Co and Re, in the amounts of between around 3 to around 10 wt. % Co and between around 0.5 to around 15 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 polycrystalline diamond construction having a substrate formed of such cemented carbide material bonded to a body of polycrystalline diamond material along an interface, the body of polycrystalline diamond material having a region adjacent the interface with the substrate which includes a plurality of diamond grains at least partially coated in rhenium carbide.

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 15 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.

2. The cemented carbide material of claim 1, wherein the cemented carbide material comprises between around 12 to around 13.5 wt % Re.

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

4. The cemented carbide material of claim 1, wherein the cemented carbide material has an associated magnetic coercive force varying from around 2 kA/m to around 70 kA/m.

5. The cemented carbide material of claim 1, further comprising a carbide of one or more metals in form of a second carbide phase, and/or dissolved in a binder phase in the cemented carbide material, said one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta.

6. The cemented carbide material as claimed in claim 5, wherein the binder phase comprises at least about 0.1 weight percent to at most about 5 weight percent of one or more of Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta in solid solution and/or in the form of a carbide compound(s).

7. The cemented carbide material of claim 1, wherein the cemented carbide material comprises a binder phase comprising a binder material, the binder material comprising a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni.

8. The cemented carbide material as claimed in claim 1, wherein the cemented carbide material comprises a carbide phase comprising WC; the cemented carbide material having a coercive force Hc in kA/m as a function of the WC mean grain size D.sub.wc in ?m determined on the basis of EBSD images of the carbide microstructure in the carbide phase equal to or less than values given by the equation: $\mathrm{Hc}=10?D_{\mathrm{wc}}^{-0.62}$

9. The cemented carbide material of claim 1, wherein the cemented carbide material has a coefficient of thermal expansion of between around 3?10.sup.?6 to around 5?10.sup.?6 at room temperature to between around 6?10.sup.?6 to around 8?10.sup.?6 at 1350 degrees Centigrade.

10. The cemented carbide material as claimed in claim 1, wherein the hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m.sup.1/2 is above around 190.

11. A polycrystalline diamond construction comprising: a substrate comprising a cemented carbide material, the cemented carbide material comprising WC, Co and Re; and a body of polycrystalline diamond material bonded to the substrate along an interface; wherein: the cemented carbide material comprises between around 3 to around 10 wt. % Co and between around 0.5 to around 15 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; and the body of polycrystalline diamond material comprising a region adjacent the interface with the substrate, said region comprising a plurality of diamond grains at least partially coated in rhenium carbide.

12. The polycrystalline diamond construction of claim 11, wherein the cemented carbide material comprises between around 12 to around 13.5 wt % Re.

13. The polycrystalline diamond construction of claim 11, wherein the body of superhard polycrystalline diamond material has inter-bonded diamond grains with interstitial spaces between the inter-bonded diamond grains, at least a portion of the interstitial spaces being substantially free of metal solvent catalyst material.

14. The polycrystalline diamond construction of claim 11, wherein the cemented carbide material has an associated magnetic coercive force varying from around 2 kA/m to around 70 kA/m.

15. The polycrystalline diamond construction of claim 11, wherein the substrate further comprises a carbide of one or more metals in form of a second carbide phase, and/or dissolved in a binder phase in the cemented carbide material, said one or more metals comprising Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta.

16. The polycrystalline diamond construction as claimed in claim 15, wherein the binder phase in the substrate comprises at least about 0.1 weight percent to at most about 5 weight percent of one or more of Ti, V, Cr, Mn, Zr, Nb, Mo, Hf and/or Ta in solid solution and/or in the form of a carbide compound(s).

17. The polycrystalline diamond construction of claim 11, wherein the cemented carbide material comprises a binder phase comprising a binder material, the binder material comprising a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni.

18. The polycrystalline diamond construction as claimed in claim 11, wherein the cemented carbide material comprises a carbide phase comprising WC; the cemented carbide material having a coercive force Hc in kA/m as a function of the WC mean grain size D.sub.wc in ?m determined on the basis of EBSD images of the carbide microstructure in the carbide phase equal to or less than values given by the equation: $\mathrm{Hc}=10?D_{\mathrm{wc}}^{-0.62}$

19. The polycrystalline diamond construction of claim 11, wherein the cemented carbide material has a coefficient of thermal expansion of between around 3?10.sup.?6 to around 5?10.sup.?6 at room temperature to between around 6?10.sup.?6 to around 8?10.sup.?6 at 1350 degrees Centigrade.

20. The polycrystalline diamond construction as claimed in claim 11, wherein the hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m.sup.1/2 is above around 190.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Examples will now be described by way of example and with reference to the accompanying drawings in which:

[0016] FIG. 1 is an SEM image of a cemented carbide material according to a first example and comprising WC-Co-Re;

[0017] FIG. 2 is an EBSD image of the WC-Co-Re cemented carbide material of FIG. 1;

[0018] FIG. 3 is an EBSD image showing the microstructure of conventional WC-Co cemented carbide material;

[0019] FIG. 4 is a plot of hot-stage XRD measurement protocol for testing an example construction and a conventional construction;

[0020] FIG. 5 is a schematic drawing of an example PCD construction comprising a body of PCD material bonded to an example substrate;

[0021] FIG. 6 is a schematic drawing of a region of the microstructure of the body of PCD material of FIG. 5;

[0022] FIG. 7 is a plot of coefficient of thermal expansion against temperature of a conventional WC-Co material and an example cemented carbide material; and

[0023] FIG. 8 is a plot showing the distribution of Co, Re and C at the interface in an example PCD construction between the substrate and the body of PCD material.

DETAILED DESCRIPTION

[0024] 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.

[0025] 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.

[0026] 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 WCNi 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 ].

[0027] As used herein, a superhard material is a material having a Vickers hardness of at least about 25 GPa. Diamond and cubic boron nitride (cBN) material are examples of superhard materials.

[0028] 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.

[0029] 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 example 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 examples 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. Examples 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.

[0030] 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 examples 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. Examples 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.

[0031] With reference to FIG. 1 and FIG. 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 example shown in FIG. 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.

[0032] FIG. 3 shows, for comparison, a conventional cemented carbide material comprising WC as the carbide phase and Co as the binder phase.

[0033] In some examples, the cemented carbide material further includes 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.

[0034] In some examples, the cemented carbide material has between around 0.5 to around 15 wt % Re, in some examples between around 0.5 to around 8 wt % Re and in other examples between around 12 to 13.5 wt % Re.

[0035] In some examples, the cemented carbide material comprises between around 3 to around 10 wt. % Co.

[0036] The WC in the cemented carbide material may, for example, have a mean grain size below around 0.6 microns.

[0037] Furthermore, in some examples, the equivalent total carbon (ETC) content with respect to WC is between around 6.3 wt % to around 6.9 wt %.

[0038] 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 4?? or magnetic moment a 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, ?, of pure Co is 16.1 micro-Tesla times cubic metre per kilogram (?T.Math.m.sup.3/kg), and the induction of saturation, also referred to as the magnetic saturation, 4??, of pure Co is 201.9 ?T.Math.m.sup.3/kg. The tungsten content within the binder may be determined from a measurement of the magnetic moment, ?, or magnetic saturation, M.sub.s=47a, 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, M.sub.s, to the concentrations of W and C in the binder:

M.sub.s?[C]/[W]?wt. % Co?201.9 in units of ?T.Math.m.sup.3/kg

[0039] Some examples 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.

[0040] Some examples of the cemented carbide material may have the following properties: density 4.97 g/cm.sup.3, magnetic coercive force 135 Oe, magnetic moment 2.4 Gcm.sup.3/g, Vickers hardness HV20 1470 and K1C 10.6 MPa.Math.m0.5.

[0041] 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.

[0042] 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 1500?. 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/?).sup.1/2 (See section 3.3.2 of ISO FDIS 13067 Microbeam analysisElectron Backscatter DiffractionMeasurement of average grain size., International Standards Organisation Geneva, Switzerland, 2011).

[0043] In some examples, the carbide phase of the cemented carbide material is formed of carbide grains having a mean grain size of at least around 0.1 ?m to at most around 10 ?m and the cemented carbide material may have an associated magnetic coercive force varying from around 2 kA/m to around 70 kA/m.

[0044] In some examples, the carbide phase comprises WC and the cemented carbide material has a coercive force Hc in kA/m as a function of the WC mean grain size D.sub.wc in ?m determined on the basis of EBSD images of the carbide microstructure equal to or less than values given by the equation:

[00001]$\mathrm{Hc}=10?D_{\mathrm{wc}}^{-0.62}$

[0045] In some examples, the carbide phase comprises WC and the binder phase comprises Co and Re.

[0046] 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 examples, 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 examples, 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.

[0047] The cemented carbide has an associated hardness and, in some examples, the hardness decrease at 300? C. is at most 20%, or, in some other examples, 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 example 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 example material.

[0048] The cemented carbide material may, for example, have a hardness decrease at 500? C. of at most 30% or, in some other examples, at most 27%.

[0049] The hardness-toughness coefficient may be calculated by multiplying the Vickers hardness in GPa and indentation fracture toughness in MPa m.sup.12, and, in some examples, this is above 150. In some examples, the cemented carbide material has a Vickers hardness

[0050] In some examples, 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.

[0051] An example 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.

[0052] Some examples are now described in more detail below and are not intended to be limiting.

Example 1

[0053] Tungsten carbide powder, wherein the WC grains had an average grain size of about 0.6 ?m 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 ?m. 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 %.

[0054] 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 %.

[0055] 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.

[0056] 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.

[0057] FIGS. 1 and 2 show SEM and EBSD images respectively of the WC-Co-Re cemented carbide formed according to Example 1, and FIG. 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 FIG. 1 and FIG. 2 has a WC mean grain size of 0.44 ?m. It will be seen that there is neither eta-phase nor free carbon nor porosity in the microstructure of both carbide materials shown in FIGS. 1 and 2. Table 1 shows the grain size distribution in the microstructure of the WC-Co-Re cemented carbide shown in FIGS. 1 and 2.

TABLE-US-00001 TABLE 1 Grain size distribution in the microstructure of the WC-Co-Re cemented carbide. Grain 0.05-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1 1-1.5 1.5-2 2-6 Size ?m ?m ?m ?m ?m ?m ?m ?m % 20.2 29.4 28.5 13.5 5.3 2.7 0.4 0

[0058] The magnetic moment of the WC-Co-Re carbide material of FIG. 1 and FIG. 2 was equal to 4.7 Gcm.sup.3/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 percent (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.sub.1C=10.5 MPa m.sup.1/2, and TRS=3700 MPa. The hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m.sup.1/2 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.

[0059] The residual stress in the Co-Re binder phase of the WC-Co-Re cemented carbide was measured using a Bruker D8 Discover diffractometer using the Cu-K? radiation. This wavelength of X-ray typically obtained diffraction information from a depth of around 5 ?m. 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 (211) 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 sin.sup.2? 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 DiffractionIssue 2. September 2005.

[0060] Two measurements of the WC-Co-Re cemented carbide were made which provided data with the compressive stress being ?11 MPa in the Phi=0 direction and ?8 MPa in the Phi=90 direction for the first measurement; and ?9 MPa 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 Gcm.sup.3/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.sub.1C=9.5 MPa m.sup.1/2, 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 ?m. 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.

[0061] 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=2?.Math.C.sub.T.sup.2(1+u), where u=(1?2 (C.sub.T/C.sub.L).sup.2)/(2?2 (C.sub.T/C.sub.L).sup.2), C.sub.L and C.sub.T are respectively the measured longitudinal and transverse speeds of sound through it and ? 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/(f.sub.1/E.sub.1+f.sub.2/E.sub.2)); E=E.sub.1.sup.f1+E.sub.1.sup.f2; and E=f.sub.1E.sub.1+f.sub.2E.sub.2; in which the different materials are divided into two portions with respective volume fractions of f.sub.1 and f.sub.2, which sum to one.

Example 2

[0062] WC powder was milled with around 13.5 wt % Re powder and around 9 wt % Co powder for 24 hours using a ball mill in a milling medium comprising hexane and around 2 wt % paraffin wax. After milling the equivalent total carbon (ETC) content with respect to WC was determined to be around 6.51 wt. %. Green bodies were pressed with the dimensions required to form the substrates for the PDC manufacture to follow, then sintered at 1490? C. for 60 min (30 min under vacuum, and 30 min HIP in Ar at a pressure of 50 Bar).

[0063] Evaluation of the example cemented carbide material then proceeded with density, magnetic characteristics measurements and a Vickers hardness measurement according to the ISO 3878 standard at a load of 300 N. The length of the Palmqvist cracks were measured at a load of 300 N for the fracture toughness measurement. Finally, the coefficient of thermal expansion was measured using a Linseis L75 twin push-rod alumina dilatometer, following the ASTM E228 protocol.

[0064] The example cemented carbide material was determined to have the following properties: density 4.97 g/cm.sup.3, magnetic coercive force 135 Oe, magnetic moment 2.4 Gcm.sup.3/g, Vickers hardness HV20 1470 and K1C 10.6 MPa.Math.m0.5. The coefficient of thermal expansion ranged from 4.7?0.1?10-6? C.-1 at room temperature, and steadily increased to 7.5?0.1?10-6? C.-1 at 1350? C.

[0065] To form an example PCD construction having a substrate formed of the above example cemented carbide material, a diamond powder blend having mean grain size of about 20 microns was sintered on the substrate at approximately 7 GPa and 1700? C., using a 6-anvil cubic press. This was followed by lapping and grinding the sintered body to the required dimensions for cutter evaluation.

[0066] A cross-section through the example PCD construction including through the body of PCD material and the substrate was EDM-cut from the construction, and was then polished for microstructural analysis on a JEOL JSM-IT700HR SEM.

[0067] To assess the thermal stability of the body of PCD material in the PCD construction, the graphitization onset temperature on the top exposed surface of the PCD material was measured using a hot stage XRD (Philips XPert). The PCD construction was heated from room temperature to 1100? C. under vacuum, XRD diffractograms at 100? C. steps were collected, and a final room temperature measurement made after cooling, following the temperature profile in FIG. 4.

[0068] Further assessment of thermal stability of the example PCD construction was carried out by heating a second polished cross-section for 1 hour (soak) at 800? C. under vacuum, followed by optical microscope inspection of the binder extrusion and associated thermally-induced cracking.

[0069] The rock cutting performance of the example PCD construction was measured using a Toshulin vertical lathe to cut granite (Paarl granite, compressive strength 180-240 MPa), and the wear scar area was measured after a set rock cutting distance, and cutting forces continuously.

[0070] A conventional control PCD construction was also formed under the same conditions and having the same diamond feed for the body of PCD material as the above example and the same substrate composition in terms of WC, Co, as the above example but without the addition of Re.

[0071] FIG. 5 shows an example PCD construction 1 for use as a cutter insert for a drill bit (not shown) for boring into the earth. The PCD construction 1 includes a body of PCD material 2 integrally bonded at an interface 12 to a substrate 10. The diamond in the body of PCD material is formed of diamond particles or grains which may be of natural or synthetic origin.

[0072] The substrate 10 is formed of an example cemented carbide material.

[0073] As shown in FIG. 6, during formation of the PCD construction 1, the interstices 24 between the diamond grains 22 may be at least partly filled with a non-super hard phase material. This non-super hard phase material, also known as a filler material may comprise residual catalyst/binder material, for example cobalt, nickel or iron.

[0074] The PCD construction 1, when used as a cutting element may be mounted in use in a bit body, such as a drag bit body (not shown).

[0075] The substrate 10 may be, for example, generally cylindrical having a peripheral surface 3, a peripheral top edge 8 and a distal free end.

[0076] The exposed surface of the PCD material 4 opposite the substrate 10 forms or comprises a working surface which also acts as a rake face in use. In some conventional cutting elements a chamfer typically extends between the working surface 4 and a cutting edge 6 and at least a part of a flank or barrel of the cutting element, the cutting edge being defined by the edge of the chamfer and the flank.

[0077] The working surface or rake face 4 of the PCD construction 1 is the surface or surfaces over which the chips of material being cut flow when the cutter is used to cut material from a body, the rake face 4 directing the flow of newly formed chips. This face 4 is commonly also referred to as the top face or working surface of the cutting element as the working surface 4 is the surface which, along with its edge, is intended to perform the cutting of a body in use. It is understood that the term cutting edge, as used herein, refers to the actual cutting edge, defined functionally as above, at any particular stage or at more than one stage of the cutter wear progression up to failure of the cutter, including but not limited to the cutter in a substantially unworn or unused state.

[0078] As used herein, chips are the pieces of a body removed from the work surface of the body being cut by the PCD construction 1 in use.

[0079] As used herein, the flank 2 of the cutter is the surface or surfaces of the cutter that passes over the surface produced on the body of material being cut by the cutter and is commonly referred to as the side or barrel of the cutter. The flank 2 may provide a clearance from the body and may comprise more than one flank face.

[0080] As used herein, a wear scar is a surface of a cutter formed in use by the removal of a volume of cutter material due to wear of the cutter. A flank face may comprise a wear scar. As a cutter wears in use, material may progressively be removed from proximate the cutting edge, thereby continually redefining the position and shape of the cutting edge, rake face and flank as the wear scar forms.

[0081] The conventional construction also had the same outer diameter and shape as the example PCD construction shown in FIG. 5 and was also subjected to the same tests.

[0082] As shown in FIG. 7, the coefficient of thermal expansion of the example PCD construction ranged from 4.7?0.1?10-6? C.-1 at room temperature, steadily increasing to 7.5?0.1?10-6? C.-1 at 1350? C. This was found to be, on average across this temperature range about 6% lower than the conventional PCD construction.

[0083] Furthermore, micrographs confirm a well sintered PCD material throughout in the example PCD construction, and an interface microstructure providing a high strength, crack-free bonding to the substrate. Importantly, the EDS (Energy-dispersive spectroscopy) analysis confirmed a uniform concentration of Re distributed homogenously throughout the PCD material in the example PCD construction indicating a successful binder infiltration process.

[0084] FIG. 8 shows the distribution of Co, Re and C in an example PCD construction at the interface between the substrate and the body of PCD material. To obtain the distribution shown in FIG. 8, the example body of PCD material in the example PCD construction was examined using a high-resolution TEM and high-resolution EDX with respect to the distribution of chemical elements at the diamond/binder interface. For the TEM measurements, cross-sectional lamellae were prepared by the focused ion beam (FIB) technique on a FEI Quanta 200 3D FIB instrument. High angle annular dark field scanning TEM (HAADF-STEM) imaging and energy-dispersive X-ray microanalysis (EDX) were carried out on a probe and image aberration corrected FEI Titan 80-200 ChemiSTEM transmission electron microscope operating at 200 kV.

[0085] FIG. 8 shows plots indicating the distribution of Co, Re and C in a region of the body of PCD material adjacent the interface with the substrate. It is seen that Re diffused to the interface forming a Re-rich (in the form a Rhenium carbide) and Co-poor layer protecting diamond in from graphitization at elevated temperatures. Whilst not wishing to be bound by any particular theory, it is believed the Rhenium carbide region in the example PCD construction means the very outer atoms of the diamond grains in this region are bonded to Re, so this blocks direct contact between diamond and Co. Graphitization is a surface phenomenon, meaning it has to start with the outside C atoms and work its way in so if the Co just encounters Re in this region, then the graphitization process may be delayed.

[0086] In assessing the thermal stability of the PCD material in the example and control PCD constructions, the hot stage XRD measurements showed the first indication of graphite formation for the control PCD construction to appear at 900? C., but for the example PCD construction only the very slightest sign of a graphite peak starts to appear at 1100? C. Thus at least a 200? C. delay to the onset of graphitization was present in the example PCD construction over the conventional PCD control construction. Furthermore, on cooldown to room temperature, the example PCD construction showed approximately 90% reduced amount of graphite formed compared to the conventional PCD control construction.

[0087] It will be seen that there is a clear difference in thermal response between the example PCD construction and conventional control PCD construction in that in the conventional PCD construction extensive binder extrusion and associated cracking was present throughout the sintered diamond network, compared to no binder extrusion, nor thermally-induced cracking for the example PCD construction. Therefore the post-heat treatment crack analysis demonstrated the suitability of the example PCD construction for thermally demanding drilling applications. Together with the hot stage XRD results this may be interpreted as demonstrating improved thermal stability of an example PCD construction over the conventional control PCD construction.

[0088] Furthermore, the granite rock cutting performance results indicated an equivalent abrasion resistance for the example PCD construction and conventional control PCD construction, with a 2-sample t-test score P=0.21 confirming no statistically significant difference between the datasets.

[0089] In some examples, the example constructions may be subjected to an acid leaching treatment to remove the residual catalyst from interstitial spaces between the grains of superhard material and further enhance thermal stability of the PCD construction.

[0090] It has now been surprising found 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. As a result, it may be possible to employ examples of the WC-Co-Re cemented carbide materials as HPHT components and to form example PCD constructions for use in drilling applications formed of a body of PCD material bonded along an interface to a cemented carbide substrate comprising particles of a metal carbide and the binder material described above.

[0091] Furthermore, it may be possible to recycle used examples 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.

[0092] 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.

[0093] 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.

[0094] Several further examples of an exemplary cemented carbide material comprising WC, Co and Re are set out below.

[0095] 1. A cemented carbide material comprising WC, Co and Re, wherein: [0096] the cemented carbide material comprises between around 3 to around 10 wt. % Co and between around 0.5 to around 15 wt. % Re, [0097] 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. % [0098] the cemented carbide material being substantially free of eta-phase and free carbon.

[0099] 2. The cemented carbide material may comprise between around 0.5 to around 6 wt % Re.

[0100] 3. The cemented carbide material may comprise between around 12 to around 13.5 wt % Re

[0101] 4. The WC in the material may have a mean grain size less than around 0.6 ?m.

[0102] 5. The cemented carbide material may have a magnetic saturation of at least around 40 percent to around 80 percent of the magnetic saturation of nominally pure Co.

[0103] 6. The cemented carbide material may have a carbide phase formed of carbide grains having a mean grain size of at least around 0.1 ?m to at most around 10 ?m.

[0104] 7. The cemented carbide material may have an associated magnetic coercive force varying from around 2 kA/m to around 70 kA/m.

[0105] 8. The cemented carbide material may further comprise 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.

[0106] 9. The cemented carbide material may comprise a binder phase having one or more residual compressive stresses.

[0107] 10. The binder phase may have one or more residual compressive stresses of between around ?5 MPa to around 100 MPa.

[0108] 11. The binder phase may comprise a binder material comprising Co, Re, W and C.

[0109] 12. The binder phase may comprise a binder material, the binder material comprising a solid solution of Re, carbon and W and one of more of Fe, Co, and Ni.

[0110] 13. The carbide phase may comprise WC; and the cemented carbide material may have a coercive force Hc in kA/m as a function of the WC mean grain size D.sub.wc in ?m determined on the basis of EBSD images of the carbide microstructure equal to or less than values given by the equation:

[00002]$\mathrm{Hc}=10?D_{\mathrm{wc}}^{-0.62}$

[0111] 14. The cemented carbide material may have a compression strength above around 5500 MPa at room temperature and at an elevated temperature of up to around 500? C.

[0112] 15. The cemented carbide material may have a Vickers hardness, and the hardness decrease at 300? C. is at most around 12%.

[0113] 16. The hardness decrease at 500? C. may be at most around 21%.

[0114] 17. The Young's Modulus of said material may be above around 700 GPa.

[0115] 18. The hardness-toughness coefficient calculated by multiplying the Vickers hardness in GPa and fracture toughness in MPa m.sup.1/2 may be above around 190.

[0116] 19. The binder phase in the cemented carbide material may have 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.

[0117] 20. The cemented carbide material may comprise 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

[0118] 21. A cutter comprising a substrate comprising the above defined cemented carbide material bonded to a body of polycrystalline superhard material adapted for a rotary drill bit for boring into the earth.

[0119] 22. 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.

[0120] 23. A method of producing the above defined cemented carbide material may comprise: [0121] 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; [0122] pressing the cemented carbide article from the mixture; [0123] 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 [0124] cooling the article from sintering the temperature to approximately 1300 degrees Centigrade (? C.).

[0125] 24. The step of cooling the article may comprise 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.

[0126] 25. The step of cooling the article may comprise cooling the article in a vacuum at a cooling rate of approximately 0.2 to 2 degrees per minute.

[0127] 26. The step of milling the cemented carbide mixture may comprise 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.

[0128] 27. A method of recycling the above defined cemented carbide material may comprise 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.

[0129] 28. A method of recycling the cemented carbide material may comprise 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.

[0130] 29. A method of recycling the cemented carbide material may comprise oxidation of the cemented carbide material to dissolve the carbide, Re and Co, and recovering the Re.

[0131] While various examples 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 examples disclosed.