Super hard construction, substrate for a super hard construction & methods of making same

Abstract

A substrate for a super hard polycrystalline construction has an interface surface, a base surface and a peripheral side surface extending between the interface surface and the base surface. The interface surface has one or more projections arranged to project from the interface surface in a first array; the first array of one or more projections having a non-circular peripheral outline, the peripheral outline having two or more linear sections, adjacent linear sections being spaced by a respective arcuate section extending therebetween. The substrate further has a recessed region adjacent a respective linear section of the peripheral outline of the first array, the recessed region extending from the peripheral side surface of the substrate towards the respective linear section of the peripheral outline of the first array.

Description

[0001] SUPER HARD CONSTRUCTION, SUBSTRATE FOR A SUPER HARD CONSTRUCTION & METHODS OF MAKING SAME

[0002] Field

[0003] This disclosure relates to super hard constructions, a substrate for a super hard construction and methods of making same, particularly but not exclusively to constructions comprising polycrystalline diamond (PCD) structures attached to a substrate and for use as cutter inserts or elements for drill bits for boring into the earth.

[0004] Background

[0005] Polycrystalline super hard materials, such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. In particular, tool inserts in the form of cutting elements comprising PCD material are widely used in drill bits for boring into the earth to extract oil or gas. The working life of super hard tool inserts may be limited by fracture of the super hard material, including by spalling and chipping, or by wear of the tool insert.

[0006] Cutting elements such as those for use in rock drill bits or other cutting tools typically have a body in the form of a substrate which has an interface end / surface and a super hard material which forms a cutting layer bonded to the interface surface of the substrate by, for example, a sintering process. The substrate is generally formed of a tungsten carbide-cobalt alloy, sometimes referred to as cemented tungsten carbide and the super hard material layer is typically polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN) or a thermally stable product TSP material such as thermally stable polycrystalline diamond. Polycrystalline diamond (PCD) is an example of a super hard material (also called a superabrasive material) comprising a mass of substantially intergrown diamond grains, forming a skeletal mass defining interstices between the diamond grains. PCD material typically comprises at least about 80 volume % of diamond and is conventionally made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa, and temperature of at least about 1 ,200°C, for example. A material wholly or partly filling the interstices may be referred to as filler or binder material.

[0007] PCD is typically formed in the presence of a sintering aid such as cobalt, which promotes the inter-growth of diamond grains. Suitable sintering aids for PCD are also commonly referred to as a solvent-catalyst material for diamond, owing to their function of dissolving, to some extent, the diamond and catalysing its re-precipitation. A solvent-catalyst for diamond is understood be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent-catalyst material. Most typically, PCD is often formed on a cobalt-cemented tungsten carbide substrate, which provides a source of cobalt solvent-catalyst for the PCD. Materials that do not promote substantial coherent intergrowth between the diamond grains may themselves form strong bonds with diamond grains, but are not suitable solvent-catalysts for PCD sintering.

[0008] Cemented tungsten carbide which may be used to form a suitable substrate is formed from carbide particles being dispersed in a cobalt matrix by mixing tungsten carbide particles / grains and cobalt together then heating to solidify. To form the cutting element with a super hard material layer such as PCD or PCBN, diamond particles or grains or CBN grains are placed adjacent the cemented tungsten carbide body in a refractory metal enclosure such as a niobium enclosure and are subjected to high pressure and high temperature so that inter-grain bonding between the diamond grains or CBN grains occurs, forming a polycrystalline super hard diamond or polycrystalline CBN layer.

[0009] In some instances, the substrate may be fully cured prior to attachment to the super hard material layer whereas in other cases, the substrate may be green, that is, not fully cured. In the latter case, the substrate may fully cure during the HTHP sintering process. The substrate may be in powder form and may solidify during the sintering process used to sinter the super hard material layer.

[0010] Cobalt has a significantly different coefficient of thermal expansion to that of diamond and, as such, for constructions where the super hard material is a polycrystalline diamond (PCD) material, upon heating of the polycrystalline diamond material during use, the cobalt in the substrate to which the PCD material is attached expands and may cause cracks to form in the PCD material, resulting in the deterioration of the PCD layer.

[0011] To reduce the residual stresses created at the interface between the substrate and the super hard layer, interface surfaces on substrates are known to have been formed with a plurality concentric annular rings projecting from the planar interface surface. Due to the difference in the coefficients of thermal expansion of the substrate and the super hard material layer, these layers contract at different rates when the cutting element is cooled after HTHP sintering. Tensile stress regions are formed on the upper surfaces of the rings, whereas compressive stress regions are formed on / in the valleys between such rings. Consequently, when a crack begins to grow in use, it may grow annularly along the entire upper surface of the annular ring where it is exposed to tensile stresses, or may grow along the entire annular valley between the projecting rings where it is exposed to compressive stresses, leading to the early failure of the cutting element. It is also known for cutting element substrate interfaces to comprise a plurality of spaced apart projections, the projections having relatively flat upper surfaces projecting from a planar interface surface.

[0012] Common problems that affect cutting elements are chipping, spalling, partial fracturing, and cracking of the super hard material layer. Another problem is cracking along the interface between the super hard material layer and the substrate and the propagation of the crack across the interface surface. These problems may result in the early failure of the super hard material layer and thus in a shorter operating life for the cutting element. Accordingly, there is a need for a cutting element having an enhanced operating life in high wear or high impact applications, such as boring into rock, with a super hard material layer in which the likelihood of cracking, chipping, and fracturing is reduced or controllable.

[0013] Summary

[0014] Viewed from a first aspect there is provided a substrate for a super hard polycrystalline construction comprising: an interface surface, a base surface and a peripheral side surface extending between the interface surface and the base surface; wherein: the substrate has a longitudinal axis; the interface surface comprises one or more projections arranged to project from the interface surface in a first array; the first array of one or more projections having a non-circular peripheral outline, the peripheral outline having two or more linear sections, adjacent linear sections being spaced by a respective arcuate section extending therebetween; and the substrate further comprises a recessed region adjacent to a respective linear section of the peripheral outline of the first array, the recessed region extending from the peripheral side surface of the substrate towards the respective linear section of the peripheral outline of the first array.

[0015] Viewed from a second aspect there is provided a polycrystalline diamond construction comprising a body of PCD material bonded to the above-defined substrate along the interface, the body of PCD material having an interface comprising one or more recesses, the projection(s) projecting from the interface of the substrate providing a matching fit with the recess(es) in the interface of the body of PCD material.

[0016] Viewed from a third aspect there is provided an earth boring drill bit comprising a body having the aforementioned super hard construction mounted thereon as a cutter element.

[0017] Viewed from a fourth aspect there is provided a method of forming the above defined super hard polycrystalline construction.

[0018] Brief description of the drawings

[0019] Non-limiting examples will now be described with reference to the accompanying drawings in which:

[0020] Figure 1 is a schematic side view of a conventional cylindrical PCD cutter element;

[0021] Figure 2 is a schematic perspective view from above of a conventional substrate of the cutting element of Figure 1 ;

[0022] Figure 3 is a schematic perspective view from above of an example substrate; and

[0023] Figure 4 is a schematic plan view of the example substrate of Figure 3; and Figure 5 is a schematic perspective view of a cutter element showing the example substrate of Figures 3 and 4 with a body of super hard material bonded thereto.

[0024] Detailed description

[0025] As used herein, a “super hard material” is a material having a Vickers hardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN) material are examples of super hard materials.

[0026] As used herein, a “super hard construction” means a construction comprising a body of polycrystalline super hard material and a substrate attached thereto.

[0027] As used herein, polycrystalline diamond (PCD) is a type of polycrystalline super hard material (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 grains 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. 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.

[0028] As used herein, PCBN (polycrystalline cubic boron nitride) material refers to a type of super hard material comprising grains of cubic boron nitride (cBN) dispersed within a matrix comprising metal or ceramic. PCBN is a further example of a super hard material. A “catalyst material” for a super hard material is capable of promoting the growth or sintering of the super hard material.

[0029] The term "substrate" as used herein means any substrate over which the super hard material layer is formed. For example, a "substrate" as used herein may be a transition layer formed over another substrate. Additionally, as used herein, the terms "radial" and "circumferential" and like terms are not meant to limit the feature being described to a perfect circle.

[0030] The super hard construction 1 shown in the attached figures may be suitable, for example, for use as a cutter insert for a drill bit for boring into the earth.

[0031] Like reference numbers are used to identify like features in all drawings.

[0032] In a conventional cutter element as shown in Figure 1 , the cutting element 1 includes a substrate 10 with a body of super hard material 11 formed on the substrate 10. The substrate 10 may be formed of a hard material such as cemented tungsten carbide. The body of super hard material 11 may be, for example, be formed of polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN), or may be a thermally stable product such as thermally stable PCD (TSP) or a combination of the two in a multi-layer construction. In the construction shown in Figure 1 , the body of super hard material 11 has a first layer 14 of thermally stable super hard material spaced from the interface 12 with the substrate 10 by a further layer 13 of super hard material.

[0033] The cutting element 1 may be mounted into a bit body such as a drag bit body (not shown). The exposed top surface 15 of the super hard material opposite the substrate 10 forms the cutting face, which is the surface which, along with its edge 16, performs the cutting in use.

[0034] At one end 12 of the substrate 10 is an interface surface 12 along which the layer of super hard material 11 is attached. In a conventional cutting element construction, the cutter element 1 including the substrate 10 is generally cylindrical and has a peripheral surface 20 and a peripheral top edge.

[0035] In the conventional cutter element 1 shown in Figures 1 and 2, the interface surface 12 includes a plurality of spaced-apart projections 22 that are arranged in a substantially annular discontinuous first array and are spaced from the peripheral surface 20 by a distance, and a second or inner substantially annular discontinuous array of projections 24 that are radially within the first array 22. The first and second arrays of projections 22, 24 typically have a circular peripheral outline.

[0036] An example substrate 30 is shown in Figures 3 and 4. The substrate 30 has a longitudinal axis 32, an interface surface 34, a base surface 36 and a peripheral side surface 38 extending between the interface surface 34 and the base surface 36. In this example, two arrays of projections 40, 42 extend from the interface surface 34. A first array 40, and a second array 42 located within the first array, are disposed around the central longitudinal axis 32 of the substrate 30 and are spaced from the peripheral side surface 38 of the substrate 30. The first array 40 may include a single projection (not shown) or a plurality of discontinuous projections as shown in Figures 3 and 4. The first array 40 has a non-circular peripheral outline 44 with four linear sections 46, adjacent linear sections 46 being spaced by an arcuate section 48 extending therebetween.

[0037] The second array 42 of projections is also formed of a plurality of discontinuous projections in the example of Figure 3 but could, in a further example, be formed of a single projection. The first and second arrays 40, 42 are substantially concentric about the longitudinal axis 32 in the example of Figures 3 and 4. The projections in the first and second arrays 40, 42 may in some examples be staggered relative to each other. As shown in Figures 3 and 4, the second array has a peripheral outline 50 which is substantially parallel to the peripheral outline 44 of the first array 40.

[0038] In some examples, one or more of the surfaces of all or a majority of the projections in the first and / or second arrays 40, 42 may extend in one or more planes which are not substantially parallel to the plane of the base 36 of the substrate 30 and / or in one or more planes which are not substantially parallel to a plane through which the longitudinal axis 32 of the substrate extends.

[0039] The substrate 30 has a recessed region 52 adjacent to and extending from the peripheral side surface 38 of the substrate 30 towards a respective planar section 46 of the peripheral outline 44 of the first array 40, and in some examples as shown in Figures 3 and 4 around midway along the respective planar section between adjacent arcuate sections 48. In the examples of Figures 3 and 4, a plurality of recessed regions 52 are shown, each one extending from the peripheral side surface 38 of the substrate 30 towards a respective planar section 46 of the peripheral outline 44 of the first array 40. the depth of the one or more recessed regions 52 may be up to around 800 microns, and in some examples may be around 750 microns. The substrate 30 in the examples shown in Figures 3 and 4 has a substantially circular cross section with the substrate 30 being generally cylindrical in form. Also, in this example, there is reflective symmetry along a plane though the central longitudinal axis 32. In some examples, the substrate may be substantially non cylindrical and may, for example, have a non circular cross sectional shape, such as a substantially square, rectangular, polygonal, segment shaped cross sectional shape.

[0040] In the example substrate is shown in Figures 3 and 4, the first array 40 has substantially square peripheral outline 44 with each linear section 46 of the peripheral outline being separated by a respective arcuate section 48. The peripheral outline 50 of the second array 42 is substantially parallel to the peripheral outline 44 of the first array 40. Additionally, the substrate 30 of Figures 3 and 4 has four recessed regions 52 or notches adjacent to and extending from the peripheral side surface 38 of the substrate 30 to a respective linear (planar) section 46 of the peripheral outline 44 of the first array 40 between adjacent arcuate sections 48, for example about midway along the respective linear sections 46.

[0041] Figure 5 shows a polycrystalline diamond construction 60 having a body of PCD material 62 bonded to an example substrate 30 such as that shown in Figures 3 and 4 along the interface 34. The body of 5 PCD material has an interface has a plurality of recesses (not shown), the projections in the first and second arrays 40, 42 projecting from the interface 34 of the substrate providing a matching fit with the recesses in the interface of the body of PCD material 62. The super hard material layer 62 may be attached to the substrate 30 by, for example, conventional brazing techniques or by sintering a body of diamond grains together with a pre-formed substrate 30 using a conventional high pressure and high temperature technique.

[0042] In some examples, the projections in the second array 42 may be positioned to radially align with the spaces between the projections in the first array 40. In further examples, the projections and spaces may be staggered, with projections in one array 40, 42 overlapping spaces in the other array 42, 40. This staggered or mis-aligned distribution of three-dimensional features on the interface surface 34 may assist in distributing compressive and tensile stresses and / or reducing the magnitude of the stress fields and / or arresting crack growth by preventing an uninterrupted path for crack growth.

[0043] As shown in Figures 3 and 4, in these examples, the interface surface 34 between the projections in the arrays 40, 42 is, for example, substantially planar and all or a majority of the projections in these arrays are shaped such that all or a majority of the surfaces of the projections are not substantially parallel to the base surface 36 or to the plane through which the longitudinal axis 32 of the substrate extends. In other examples, the interface surface may be substantially non planar between projections and one or more of the surfaces of the projections may be substantially parallel to the base surface 36 or to the plane through which the longitudinal axis 32 of the substrate extends.

[0044] The projections in the arrays 40, 42 may have a smoothly curving upper surface or may have a sloping upper surface. In some examples, the projections may be slightly trapezoidal or tapered in shape, being widest nearer the interface surface from which they project.

[0045] It is believed that such a configuration acts to disturb ‘elastic’ wave formation in the material and deflect cracks at the interface 34.

[0046] In Figures 3 and 4, the projections in the arrays 40, 42 are spaced substantially equally in / round the respective substantially annular array, with each projection within a given array having the same dimension. However, the projections may be formed in any desired shape, as described above, and spaced apart from each other in a uniform or non-uniform manner to alter the stress fields over the interface surface 34. In further examples, the projections in the outer array 40 may be larger in size than those in the inner array 42.

[0047] In the example shown in Figures 3 and 4, the outer array 40 includes the same number of projections as the inner array 42, namely eight projections, but in other examples the number of projections in each array may differ.

[0048] In an example where the cross-section of the substrate is substantially noncircular and has three or more planar peripheral surface regions separated by a respective arcuate surface region with an associated notch or recess 52 therein, this configuration may permit the substrate 30 to have rotational symmetry. This may have a number of advantages including assisting in location of the end construction in an associated tool, and assisting in orienting the substrate when processing to achieve the end product shape and also may assist in enabling the end product to be rotated for re-use once a section of the product of which this forms the substrate has worn to its limit. The specific orientation of the cutter in which this forms a substrate in the tool or drill bit in which it is to be used would easily be identified by the notches 52 or recesses which are visible in the end product.

[0049] The arrangement and shape of the projections in the arrays 40, 42 may affect the stress distributions in the substrate 30 and may act to improve resistance to crack growth in the end product in use, in particular crack growth along the interface surface 34, for example by arresting or diverting crack growth across the stress zones in, around and above the projections.

[0050] As shown in the example of Figure 5, the depth of super hard material in the region filling the recesses or notches 52 in the substrate 30 is greater than the depth of the super hard material at the centre of the super hard material layer. Whilst not wishing to be bound by any theory, this may enable greater compaction of superhard material in the region of each trench when forming the polycrystalline superhard construction such as that shown in Figure 5. This is believed to enable the creation of zones or regions within the polycrystalline superhard construction where the compaction of superhard material in the formation of the construction is amplified compared to the compaction in other regions of the polycrystalline superhard layer in the construction which may assist in creating regions of enhanced abrasion resistance. This is believed to assist in extending the working life of the construction 60 and may for example keep the wear scar in the super hard material for longer than conventional polycrystalline superhard constructions having a substantially unform depth across the working surface which may improve the lifespan of the cutter element 60.

[0051] In some examples, the substrate may be formed of a cemented carbide material such as tungsten carbide (WC) including a binder phase. The binder phase may include, for example, any one or more of a solid solution of Re, carbon and W and / or any one of more of Fe, Co, and Ni. In some examples, the binder phase may have 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 forming the substrate 30 may have 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.

[0052] An example of a cemented carbide material may be made by a method including milling a cemented carbide mixture containing WC with any one or more of 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.

[0053] In some examples, the substrate 30 may include excess carbon which is understood to be carbon that is in excess of the diamond of the diamond grains provided in an aggregated mass for sintering PCD which is to be bonded to the substrate in the formation of a super hard construction such as the cutter element of Figure 5, and is also in excess of the carbon included as the carbide of the cemented carbide (stochiometric excess). A carburised substrate or carburised substrate assembly is therefore a substrate or substrate assembly including excess carbon. Carbon may be introduced into the substrate 30 in any of a number of ways. In one example a substrate pre-form is prepared by a method including introducing diamond particles into the starting powders for making a cemented carbide to form a starting powder blend; forming the starting powder blend by means of compaction in a mould to form a green body; and sintering the green body at a temperature of greater than about 1 ,400 degrees centigrade at an applied pressure of less than about 1 GPa to produce a sintered substrate. At least some of the diamond particles are converted wholly or partially into graphite during this carbide sintering step, because the pressure is below that for diamond to be thermodynamically stable.

[0054] The sintering pressure at which diamond is thermodynamically stable is preferably at least about 5.5GPa and the temperature is preferably at least about 1 ,400 degrees centigrade.

[0055] In some examples, carbon may be introduced into the substrate in the form of graphite powder.

[0056] In other examples, carbon may be introduced into the substrate in the form of carbonaceous gas, which is caused to permeate or infiltrate the substrate.

[0057] In still further examples, material comprising carbon may be sprayed onto a surface of the substrate. In particular, powder containing cobalt, carbon and tungsten may be deposited onto the substrate surface by means of thermal spraying.

[0058] In other examples, the substrate may be coated with a source of excess carbon, such as graphite. In some examples, the substrate is prepared from starting carbide powder having a high content of carbon in the form of carbon black, for example.

[0059] In other examples, a substrate with high carbon content may be prepared by avoiding the removal of some carbon during the preparation of the green body for readiness for sintering. Typically, a green body is heat treated to remove binder or pressing aid material prior to sintering, and carbon is removed during this process. In one example, this process is not thoroughly completed, leaving at least some carbon of binder origin within the green body.

[0060] In one example, the method includes forming a carburised substrate, wherein the source of excess carbon is included in or introduced into the volume of the substrate. In some examples the source of excess carbon is dispersed substantially throughout the entire volume of the carburised substrate. In other examples the source of excess carbon is dispersed in a surface region proximate or adjacent the bonding surface.

[0061] In some examples, the mean content of the source of excess carbon within a surface region of an example carburised substrate or throughout substantially the entire carburised substrate is no greater than about 10 weight percent, more preferably no greater than about 6 weight percent and yet more preferably no greater than about 5.5 weight percent of the material in the surface region or the substrate. For example, the content of the source of excess carbon within the surface region or throughout the entire carburised substrate may be at least about 0.1 weight percent or at least about 0.3 weight percent of the material in the region. In some examples, such a surface region may extend to a depth of at least about 1 mm, at least about 2 mm, or even at least 3 mm from the interface surface 34. In some examples, the source of excess carbon is a carbonaceous material other than metal carbide, such as carbon black powder or graphite. In one example, the source of excess carbon may be derived from diamond that has been converted into a non-diamond material.

[0062] In one example, the method includes combining source of excess carbon in particulate or granular form with raw materials for the cemented carbide, forming the combination into a substantially self-supporting green body, and sintering the green body at a pressure at which diamond is not thermodynamically stable to form the carburised substrate. In some examples the raw materials for cemented carbide comprise grains of tungsten carbide and grains comprising cobalt.

[0063] The method of forming an example substrate may include combining diamond grains with raw materials for cemented carbide, forming the combination into a substantially self-supporting green body; subjecting the green body to a temperature of at least 500 degrees centigrade and a pressure at which diamond is not thermodynamically stable to form the carburised substrate. The diamond particles may be wholly or partly converted into a non-diamond material, particularly graphite.

[0064] A first substrate element for use as the surface region of a substrate for a PCD compact may be manufactured by blending together diamond particles, tungsten carbide (WC) powder and cobalt powder, forming the blended mixture into a compacted green body, and subjecting the green body to a conventional carbide sintering process. The diamond particles may, for example, have a mean size in the range of 0.75 to 1.5 microns, and constitute 3 weight percent of the blended mixture in one example. The WC powder and the cobalt powder may be pre-mixed, the cobalt constituting 13 weight percent of the WC-Co pre-mix and the WC particles having a mean size in the range from about 1 to 4 microns. About 2 weight percent organic pressing aid may be included in the WC-Co mix in such an example. The blended powder mix may be uniaxially compacted at ambient temperature to form a substantially cylindrical green body, which may be conventionally sintered at a temperature of 1 ,400 degrees centigrade for 2 hours to form a sintered article. By the end of the sintering process, the diamond particles may have completely converted into graphite.

[0065] To form a PCD construction having such an example substrate, a layer comprising an unbonded aggregated mass of diamond grains may then be deposited onto the interface surface of the example substrate to form an unbonded pre-sinter assembly. The assembly may be mounted within a capsule for an HPHT furnace, as is known in the art. The capsule may be subjected to a pressure of at least about 5.5 GPa and a temperature of at least about 1 ,250 degrees centigrade or more for a period of between about 5 minutes to about several hours. After sintering, the substrate element will be bonded to a body of PCD material generated during the sintering process along the interface 34 to form a PCD construction. The construction may be cylindrical such as that shown in Figure 5 with a body of PCD material bonded thereto or may be non-cylindrical.

[0066] In some examples, 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 8 GPa or above.

[0067] In one or more of the above-described examples, the projections in the arrays 40, 42 on the interface surface 34 may be formed integrally whilst the substrate 30 is being formed, through use of an appropriately shaped mold into which the particles of material to form the substrate are placed. Alternatively, the projections in the arrays 40, 42 may be created after the substrate 30 has been created or part way through the creation process, for example by a conventional machining process such as EDM or by laser ablation.

[0068] In an example where the substrate 30 includes Re, an example method of manufacture may be as follows. A mass of tungsten carbide powder having WC grains having an average grain size of about 0.6 pm with a carbon content of 6.13 wt.%, may be milled with 5.5%Re powder and 3.7%Co powder. The Co grains may have an average grain size of about 1 pm. The powder mixture may be 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 may be added and additional milling performed for 1 hr. After drying the mixture, green bodies may be 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 may be cooled down to 1300°C at a rate of 0.5 degrees per min and afterwards at an uncontrolled rate down to room temperature.

[0069] In some examples, as described above, the cemented carbide material forming the substrate may comprise between around 2 to around 15 wt.% Re, and around 3 to around 9 wt.%Co, with the remainder being WC.

[0070] Similar procedures may be applied to the super hard material layer 32 to create the corresponding shaped interface surface for forming a matching fit with that of the substrate, or such a matching fit may be created in the interface of the super hard material layer by placing the particles of super hard material onto a pre-formed substrate and subjecting the combination to the sintering process such that the matching interface in the super hard material layer is formed during sintering. The durability of the cutter product 60 including an example substrate 30 and super hard material layer 62 may be further enhanced if the super hard material layer 62 is leached of catalyst material, either partially or fully, in subsequent processing, or subjected to a further high pressure high temperature sintering process. The leaching may be performed whilst the super hard material layer 32 is attached to the substrate 30 using conventional leaching techniques known in the art.

[0071] Although the examples shown in Figures 3 to 5 are shown as having a substantially cylindrical cross-section, example substrates may have another non-cylindrical cross-section shape such as substantially square, rectangular, or substantially triangular, for example with rounded corners in each case.

[0072] In the example where the construction is formed in the sintering process with a substantially cylindrical shape and processed post sintering to generate the desired end shape, the arcuate portions of the peripheral side surfaces may be formed from the curvature of the initial cylindrical shape.

[0073] To achieve the final desired shape of the substrate, the substrate may be machined such as through application of a lapping process or laser ablated to a non-cylindrical shape either before or after attachment to body of PCD material to form a cutter element such as that shown in Figure 7.

[0074] In some examples, machining the substrate and / or cutter element to the final shape, through laser ablation or lapping as examples, may remove the notches 52 in the substrate and, in the case of a cutter element, the projections of super hard material filling those notches 52, to achieve the final product. The notches 52 in such an example may assist as a means of aligning the substrate and / or cutter element in the final machining process to achieve the desired final shape and dimensions of the substrate and / or cutter element. In some examples, the final shape may be generated in situ during the HPHT process used to produce the substrate and / or cutter element using appropriately shaped molds in the sintering capsule.

Claims

Claims:1 . A substrate for a super hard polycrystalline construction comprising: an interface surface, a base surface and a peripheral side surface extending between the interface surface and the base surface; wherein: the substrate has a longitudinal axis; the interface surface comprises one or more projections arranged to project from the interface surface in a first array; the first array of one or more projections having a non-circular peripheral outline, the peripheral outline having two or more linear sections, adjacent linear sections being spaced by a respective arcuate section extending therebetween; and the substrate further comprises a recessed region adjacent to a respective linear section of the peripheral outline of the first array, the recessed region extending from the peripheral side surface of the substrate towards the respective linear section of the peripheral outline of the first array.

2. The substrate of claim 1 , further comprising a plurality of recessed regions extending from the peripheral side surface of the substrate towards respective linear sections of the peripheral outline of the first array.

3. The substrate of any one of claims 1 or 2, wherein one or more of the recessed regions are located in said substrate at a position spaced from the peripheral outline of the first array and substantially midway along the respective linear section of the peripheral outline of the first array.

4. The substrate of any one of the preceding claims, wherein the first array is discontinuous and comprises a plurality of projections arranged around the longitudinal axis, the projections being spaced from the peripheral side surface of the substrate.

5. The substrate of any one of the preceding claims, wherein the interface surface further comprises a second discontinuous array of projections within the first array.

6. The substrate of claim 5, wherein the first and second arrays are substantially concentric about the longitudinal axis.

7. The substrate of claim 6, wherein the projections in the first and second arrays are staggered relative to each other.

8. The substrate of any one of claims 5 to 7, wherein the second array has a peripheral outline, the peripheral outlines of the first and second arrays being substantially parallel.

9. The substrate of any one of the preceding claims, wherein the peripheral outline of the first array is substantially parallel to the peripheral side surface of the substrate.

10. The substrate of any one of the preceding claims, wherein one or more of the surfaces of all or a majority of the projections extend in one or more planes which are not substantially parallel to the plane of the base of the substrate and / or in one or more planes which are not substantially parallel to a plane through which the longitudinal axis of the substrate extends.

11. The substrate of any one of the preceding claims, comprising a cemented carbide material.

12. The substrate of claim 11 , wherein the cemented carbide material comprises tungsten carbide.

13. The substrate of any one of claims 11 or 12, further comprising tungsten carbide particles bonded together by a binder material, the binder material comprising an alloy of Co, Ni and Cr.

14. The substrate of claim 13, wherein the binder material further comprises one or more of V, Ta, Ti, Mo, Zr, Nb and Hf in solid solution.

15. The substrate of any one of claims 13 or 14, further comprising one or more of Re, Ru, Rh, Pd, Re, Os, Ir and Pt.

16. The substrate of any one of the preceding claims, further comprising free carbon.

17. The substrate of any one of the preceding claims, wherein the substrate has a circular cross-section in a plane perpendicular to a plane through which the longitudinal axis extends.

18. The substrate of any one of the preceding claims, wherein the substrate has a non-circular cross-section in a plane perpendicular to a plane through which the longitudinal axis extends19. The substrate of claim 18, wherein the cross-section of the substrate is substantially square.

20. The substrate of claim 18, wherein the cross-section of the substrate is substantially rectangular.21 . The substrate of claim 18, wherein the cross-section of the substrate is substantially triangular.

22. A polycrystalline diamond construction comprising a body of PCD material bonded to the substrate of any one of the preceding claims along the interface, the body of PCD material having an interface comprising one or more recesses, the projection(s) projecting from the interface of the substrate providing a matching fit with the recess(es) in the interface of the body of PCD material.

23. An earth-boring tool, comprising: a body; andat least one cutting element comprising the polycrystalline diamond construction of claim 22 attached to the body.

24. An earth boring drill bit comprising the polycrystalline diamond construction of claim 22 mounted thereon or therein as a cutter element.

25. A method of forming the super hard polycrystalline construction of any one of claims 1 to 22 comprising: a first stage, the first stage comprising providing the substrate; a second stage, the second stage comprising placing the substrate in a canister having an internal peripheral wall defining a recess for receiving the substrate, the internal peripheral wall having a non-circular outline matching the peripheral side surface of the substrate; a third stage; the third stage comprising placing an aggregated mass of particles or grains of super hard material into the canister over the interface surface of the substrate to form a pre-sinter assembly; a fourth stage; the fourth stage comprising sealing the cannister is sealed, and subjecting the pre-sinter assembly to a pressure of greater than around 5.5 GPa at a temperature of at least around 1250 degrees celcius to sinter the particles or grains and form the super hard polycrystalline construction comprising the body of super hard polycrystalline material bonded to the substrate; a fifth stage; the fifth stage comprising removing the super hard polycrystalline construction from the canister.

26. A method of forming the super hard polycrystalline construction of any one of claims 1 to 22 comprising: a first stage, the first stage comprising providing the substrate;a second stage, the second stage comprising placing the substrate in a canister; a third stage, the third stage comprising placing an aggregated mass of particles or grains of super hard material into the canister over the interface surface of the substrate to form a pre-sinter assembly; a fourth stage, the fourth stage comprising sealing the cannister is sealed, and subjecting the pre-sinter assembly to a pressure of greater than around 5.5 GPa at a temperature of at least around 1250 degrees Celsius to sinter the particles or grains and form the super hard polycrystalline construction comprising the body of super hard polycrystalline material bonded to the substrate; a fifth stage, the fifth stage comprising removing the super hard polycrystalline construction from the canister; and a sixth stage, the sixth stage comprising processing the super hard polycrystalline construction to shape the body of super hard polycrystalline material to have a non-circular cross section in a plane perpendicular to a plane through which the longitudinal axis extends by shaping the peripheral side surface of the body of super hard polycrystalline material to comprise two or more planar surface regions, wherein adjacent planar surface regions are spaced by a respective arcuate surface region extending therebetween.

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