GB2533868A

GB2533868A - Superhard constructions & methods of making same

Info

Publication number: GB2533868A
Application number: GB1523147.5A
Authority: GB
Inventors: Serdar Ozbayraktar Mehmet
Original assignee: Element Six UK Ltd
Current assignee: Element Six UK Ltd
Priority date: 2014-12-31
Filing date: 2015-12-31
Publication date: 2016-07-06
Also published as: GB201523147D0; GB201423410D0; WO2016107925A1

Abstract

A super hard polycrystalline construction comprising (i) a body of polycrystalline super hard material having a super hard phase with (ii) inter-bonded grains having interstitial spaces there between in which is dispersed a non-super hard phase and where (iii) the non-super hard phase occupies substantially 3-5 volume % of the total volume of the construction.

Description

SUPERHARD CONSTRUCTIONS & METHODS OF MAKING SAME

Field

This disclosure relates to super hard constructions and methods of making such constructions, particularly but not exclusively to constructions comprising polycrystalline diamond (PCD) structures attached to a substrate, and tools comprising the same, particularly but not exclusively for use in rock degradation or drilling, or for boring into the earth.

Background

Polycrystalline super hard materials, such as polycrystalline diamond (PCD) 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.

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), 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 super abrasive material or ultra hard material) comprising a mass of substantially inter-grown 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.

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.

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, diamond particles or 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 occurs, forming a polycrystalline super hard diamond layer.

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.

Ever increasing drives for improved productivity in the earth boring field place ever increasing demands on the materials used for cutting rock. Specifically, PCD materials with improved abrasion and impact resistance are required to achieve faster cut rates and longer tool life.

Cutting elements or tool inserts comprising PCD material are widely used in drill bits for boring into the earth in the oil and gas drilling industry. Rock drilling and other operations require high abrasion resistance and impact resistance. One of the factors limiting the success of the polycrystalline diamond (PCD) abrasive cutters is the generation of heat due to friction between the PCD and the work material. This heat causes the thermal degradation of the diamond layer. The thermal degradation increases the wear rate of the cutter through increased cracking and spalling of the PCD layer as well as back conversion of the diamond to graphite causing increased abrasive wear.

Methods used to improve the abrasion resistance of a PCD composite often result in a decrease in impact resistance of the composite.

The most wear resistant grades of PCD usually suffer from a catastrophic fracture of the cutter before it has worn out. During the use of these cutters, cracks grow until they reach a critical length as which catastrophic failure occurs, namely, when a large portion of the PCD breaks away in a brittle manner. These long, fast growing cracks encountered during use of conventionally sintered PCD, result in short tool life.

Furthermore, despite their high strength, polycrystalline diamond (PCD) materials are usually susceptible to impact fracture due to their low fracture toughness. Improving fracture toughness without adversely affecting the material's high strength and abrasion resistance is a challenging task.

There is therefore a need for a polycrystalline super hard composite such as a PCD composite that has good or improved abrasion, fracture and impact resistance and a method of forming such composites.

Summary

Viewed from a first aspect there is provided a superhard polycrystalline construction comprising: a body of polycrystalline superhard material, the body of polycrystalline superhard material comprising: a superhard phase comprising interbonded grains having interstitial spaces therebetween, and a non-super hard phase dispersed in the interstitial spaces; wherein the non-super hard phase occupies between around 3 vol% to around 5 vol% of the total volume of the body of polycrystalline superhard material Viewed from a second aspect there is provided a method of forming the above defined construction.

BRIEF DESCRIPTION OF THE DRAWINGS

Versions will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of an example PCD cutter element for a drill bit for boring into the earth; Figure 2 is a schematic cross-section of an example portion of a PCD microstructure; Figure 3 is a parts exploded view of the components to form the PCD cutter element of Figure 1 being loaded into a capsule for sintering; Figure 4 is a plot showing the results of a test showing the wear scar size obtained during testing of PCD constructions of various binder contents expressed as vol% of the total polycrystalline body; and Figure 5 is a plot showing the results of a test showing the wear scar size obtained during testing of PCD constructions of various binder contents expressed as voN/0 of the total polycrystalline body.

The same references refer to the same general features in all the drawings. DESCRIPTION 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.

As used herein, a "super hard construction" means a construction comprising a body of polycrystalline super hard material. In such a construction, a substrate may be attached thereto or alternatively the body of polycrystalline material may be free-standing and unbacked.

As used herein, polycrystalline diamond (PCD) is a type of polycrystalline super hard (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.

A "catalyst material" for a super hard material is capable of promoting the growth or sintering of the super hard material.

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.

As used herein, the term "integrally formed" regions or parts are produced contiguous with each other and are not separated by a different kind of material.

In an example as shown in Figure 1, a cutting element 1 includes a layer of super hard material 2 formed on a substrate 3. The substrate 3 may be formed of a hard material such as cemented tungsten carbide. The super hard material 2 may be, for example, polycrystalline diamond (PCD), or a thermally stable product such as thermally stable PCD (TSP). The cutting element 1 may be mounted into a bit body such as a drag bit body (not shown) and may be suitable, for example, for use as a cutter insert for a drill bit for boring into the earth.

The exposed top surface of the super hard material opposite the substrate forms the cutting face 4, which is the surface which, along with its edge 6, performs the cutting in use.

At one end of the substrate 3 is an interface surface 8 that forms an interface with the super hard material layer 2 which is attached thereto at this interface surface. As shown in the example of Figure 1, the substrate 3 is generally cylindrical and has a peripheral surface 10 and a peripheral top edge 12.

As used herein, a PCD grade is a PCD material characterised in terms of the volume content and size of diamond grains, the volume content of interstitial regions between the diamond grains and composition of material that may be present within the interstitial regions. A grade of PCD material may be made by a process including providing an aggregate mass of diamond grains having a size distribution suitable for the grade, optionally introducing catalyst material or additive material into the aggregate mass, and subjecting the aggregated mass in the presence of a source of catalyst material for diamond to a pressure and temperature at which diamond is more thermodynamically stable than graphite and at which the catalyst material is molten. Under these conditions, molten catalyst material may infiltrate from the source into the aggregated mass and is likely to promote direct intergrowth between the diamond grains in a process of sintering, to form a PCD structure. The aggregate mass may comprise loose diamond grains or diamond grains held together by a binder material and said diamond grains may be natural or synthesised diamond grains.

Different PCD grades may have different microstructures and different mechanical properties, such as elastic (or Young's) modulus E, modulus of elasticity, transverse rupture strength (TRS), toughness (such as so-called KiC toughness), hardness, density and coefficient of thermal expansion (CTE). Different PCD grades may also perform differently in use. For example, the wear rate and fracture resistance of different PCD grades may be different.

All of the PCD grades may comprise interstitial regions filled with material comprising cobalt metal, which is an example of catalyst material for diamond.

The PCD structure 2 may comprise one or more PCD grades.

Figure 2 is a cross-section through an example of PCD material forming the super hard layer 2 of Figure 1 showing, schematically, the PCD microstructure. As shown in Figure 2, the diamond grains are directly inter-bonded to adjacent grains and the interstices 24 between the grains 22 of super hard material such as diamond grains in the case of PCD, 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. In examples of super hard, for example PCD material, the non-super hard phase comprises between around 3 vol% to around 5 vol% of the super hard layer 2.

The grains of super hard material may be, for example, diamond grains or particles. In the starting mixture prior to sintering they may be, for example, bimodal, that is, the feed comprises a mixture of a coarse fraction of diamond grains and a fine fraction of diamond grains. In some examples, the coarse fraction may have, for example, an average particle/grain size ranging from about 10 to 60 microns. By "average particle or grain size" it is meant that the individual particles/grains have a range of sizes with the mean particle/grain size representing the "average". The average particle/grain size of the fine fraction is less than the size of the coarse fraction. For example, the fine fraction may have an average grain size of between around 1/10 to 6/10 of the size of the coarse fraction, and may, in some examples, range for example between about 0.1 to 20 microns.

In some examples, the weight ratio of the coarse diamond fraction to the fine diamond fraction may range from about 50% to about 97% coarse diamond and the weight ratio of the fine diamond fraction may be from about 3% to about 50%. In other examples, the weight ratio of the coarse fraction to the fine fraction may range from about 70:30 to about 90:10.

In further examples, the weight ratio of the coarse fraction to the fine fraction may range for example from about 60:40 to about 80:20.

In some examples, the particle size distributions of the coarse and fine fractions do not overlap and in some examples the different size components of the compact are separated by an order of magnitude between the separate size fractions making up the multimodal distribution.

Some examples consist of a wide bi-modal size distribution between the coarse and fine fractions of super hard material, but some examples may include three or even four or more size modes which may, for example, be separated in size by an order of magnitude, for example, a blend of particle sizes whose average particle size is 20 microns, 2 microns, 200nm and 20nm.

Sizing of diamond particles/grains into fine fraction, coarse fraction, or other sizes in between, may be through known processes such as jet-milling of larger diamond grains and the like.

In examples where the super hard material is polycrystalline diamond material, the diamond grains used to form the polycrystalline diamond material may be natural and/or synthetic.

In some examples, the binder catalyst/solvent may comprise cobalt or some other iron group elements, such as iron or nickel, or an alloy thereof. Carbides, nitrides, borides, and oxides of the metals of Groups IV-VI in the periodic table are other examples of non-diamond material that might be added to the sinter mix. In some examples, the binder/catalyst/sintering aid may be Co. The cemented metal carbide substrate may be conventional in composition and, thus, may be include any of the Group IVB, VB, or VIB metals, which are pressed and sintered in the presence of a binder of cobalt, nickel or iron, or alloys thereof. In some examples, the metal carbide is tungsten carbide.

The cutter of Figure 1 having the microstructure of Figure 2 may be fabricated, for example, as follows.

As used herein, a "green body" is a body comprising grains to be sintered and a means of holding the grains together, such as a binder, for example an organic binder.

Examples of super hard constructions may be made by a method of preparing a green body comprising grains or particles of super hard material, second phase and a binder, such as an organic binder. The green body may also comprise catalyst material for promoting the sintering of the super hard grains. The green body may be made by combining the grains or particles with the binder/catalyst and forming them into a body having substantially the same general shape as that of the intended sintered body, and drying the binder. At least some of the binder material may be removed by, for example, burning it off. The green body may be formed by a method including a compaction process, an injection process or other methods such as molding, extrusion, deposition modelling methods.

A green body for the super hard construction may be placed onto a substrate, such as a pre-formed cemented carbide substrate to form a pre-sinter assembly, which may be encapsulated in a capsule for an ultra-high pressure furnace, as is known in the art. The substrate may provide a source of catalyst material for promoting the sintering of the super hard grains. In some examples, the super hard grains may be diamond grains and the substrate may be cobalt-cemented tungsten carbide, the cobalt in the substrate being a source of catalyst for sintering the diamond grains. The pre-sinter assembly may comprise an additional source of catalyst material.

In one version, the method may include loading the capsule comprising a pre-sinter assembly into a press and subjecting the green body to an ultrahigh pressure and a temperature at which the super hard material is thermodynamically stable to sinter the super hard grains. In some examples, the green body may comprise diamond grains and the pressure to which the assembly is subjected is at least about 5 GPa and the temperature is at least about 1,300 degrees centigrade.

A version of the method may include making a diamond composite structure by means of a method disclosed, for example, in PCT application publication number W02009/128034. A powder blend comprising diamond particles, and a metal binder material, such as cobalt may be prepared by combining these particles and blending them together. An effective powder preparation technology may be used to blend the powders, such as wet or dry multi-directional mixing, planetary ball milling and high shear mixing with a homogenizer. In one embodiment, the mean size of the diamond particles may be at least about 50 microns and they may be combined with other particles by mixing the powders or, in some cases, stirring the powders together by hand. In one version of the method, precursor materials suitable for subsequent conversion into binder material may be included in the powder blend, and in one version of the method, metal binder material may be introduced in a form suitable for infiltration into a green body. The powder blend may be deposited in a die or mold and compacted to form a green body, for example by uni-axial compaction or other compaction method, such as cold isostatic pressing (CIP). The green body may be subjected to a sintering process known in the art to form a sintered article. In one version, the method may include loading the capsule comprising a pre-sinter assembly into a press and subjecting the green body to an ultrahigh pressure and a temperature at which the super hard material is thermodynamically stable to sinter the super hard grains.

After sintering, the polycrystalline super hard constructions may be ground to size and may include, if desired, a 45° chamfer of approximately 0.4mm height on the body of polycrystalline super hard material so produced.

The sintered article may be subjected to a subsequent treatment at a pressure and temperature at which diamond is thermally stable to convert some or all of the non-diamond carbon back into diamond and produce a diamond composite structure. An ultra-high pressure furnace well known in the art of diamond synthesis may be used and the pressure may be at least about 5.5 GPa and the temperature may be at least about 1,250 degrees centigrade for the second sintering process.

A further example of a super hard construction may be made by a method including providing a PCD structure and a precursor structure for a diamond composite structure, forming each structure into the respective complementary shapes, assembling the PCD structure and the diamond composite structure onto a cemented carbide substrate to form an unjoined assembly, and subjecting the unjoined assembly to a pressure of at least about 5.5 GPa and a temperature of at least about 1,250 degrees centigrade to form a PCD construction. The precursor structure may comprise carbide particles and diamond or non-diamond carbon material, such as graphite, and a binder material comprising a metal, such as cobalt. The precursor structure may be a green body formed by compacting a powder blend comprising particles of diamond or non-diamond carbon and particles of carbide material and compacting the powder blend.

In some examples, both the bodies of, for example, diamond and carbide material and sintering aid/binder/catalyst are applied as powders and sintered simultaneously in a single UHP/HT process. The mixture of diamond grains, and mass of carbide are placed in an HP/HT reaction cell assembly and subjected to HP/HT processing. The HP/HT processing conditions selected are sufficient to effect intercrystalline bonding between adjacent grains of abrasive particles and, optionally, the joining of sintered particles to the cemented metal carbide support. In one example, the processing conditions generally involve the imposition for about 3 to 120 minutes of a temperature of at least about 1200 degrees C and an ultra-high pressure of greater than about 5 GPa.

In another example, the substrate may be pre-sintered in a separate process before being bonded together in the HP/HT press during sintering of the ultrahard polycrystalline material.

In a further example, both the substrate and a body of polycrystalline super hard material are pre-formed. For example, the bimodal feed of ultrahard grains/particles with optional carbonate binder-catalyst also in powdered form are mixed together, and the mixture is packed into an appropriately shaped canister and is then subjected to extremely high pressure and temperature in a press. Typically, the pressure is at least 5 GPa and the temperature is at least around 1200 degrees C. The preformed body of polycrystalline superhard material is then placed in the appropriate position on the upper surface of the preform carbide substrate (incorporating a binder catalyst), and the assembly is located in a suitably shaped canister. The assembly is then subjected to high temperature and pressure in a press, the order of temperature and pressure being again, at least around 1200 degrees C and 5 GPa respectively. During this process the solvent/catalyst migrates from the substrate into the body of superhard material and acts as a binder-catalyst to effect intergrowth in the layer and also serves to bond the layer of polycrystalline superhard material to the substrate. The sintering process also serves to bond the body of superhard polycrystalline material to the substrate.

Solvent / catalyst for diamond may be introduced into the aggregated mass of diamond grains by various methods, including blending solvent / catalyst material in powder form with the diamond grains, depositing solvent / catalyst material onto surfaces of the diamond grains, or infiltrating solvent / catalyst material into the aggregated mass from a source of the material other than the substrate, either prior to the sintering step or as part of the sintering step. Methods of depositing solvent / catalyst for diamond, such as cobalt, onto surfaces of diamond grains are well known in the art, and include chemical vapour deposition (CVD), physical vapour deposition (PVD), sputter coating, electrochemical methods, electroless coating methods and atomic layer deposition (ALD). It will be appreciated that the advantages and disadvantages of each depend on the nature of the sintering aid material and coating structure to be deposited, and on characteristics of the grain.

In one example, the binder/catalyst such as cobalt may be deposited onto surfaces of the diamond grains by first depositing a pre-cursor material and then converting the precursor material to a material that comprises elemental metallic cobalt. For example, in the first step cobalt carbonate may be deposited on the diamond grain surfaces using the following reaction: Co(NO3)2 + Na2CO3 -> CoCO3 + 2NaNO3 The deposition of the carbonate or other precursor for cobalt or other solvent / catalyst for diamond may be achieved by means of a method described in PCT patent publication number WO/2006/032982. The cobalt carbonate may then be converted into cobalt and water, for example, by means of pyrolysis reactions such as the following: CoCO3 -> CoO + CO2 CoO + H2 -> CO + H2O In another example, cobalt powder or precursor to cobalt, such as cobalt carbonate, may be blended with the diamond grains. Where a precursor to a solvent / catalyst such as cobalt is used, it may be necessary to heat treat the material in order to effect a reaction to produce the solvent / catalyst material in elemental form before sintering the aggregated mass.

In some examples, the cemented carbide substrate may be formed of tungsten carbide particles bonded together by the binder material, the binder material comprising an alloy of Co, Ni and Cr. The tungsten carbide particles may form at least 70 weight percent and at most 95 weight percent of the substrate. The binder material may comprise between about 10 to 50 wt.% Ni, between about 0.1 to 10 wt.% Cr, and the remainder weight percent comprises Co. The PCD element 10 described with reference to Figure 1 may be further processed after sintering. For example, catalyst material may be removed from a region of the PCD structure adjacent the working surface or the side surface or both the working surface and the side surface. This may be done by treating the PCD structure with acid to leach out catalyst material from between the diamond grains, or by other methods such as electrochemical methods. A thermally stable region, which may be substantially porous, extending a depth of at least about 50 microns or at least about 100 microns from a surface of the PCD structure, may thus be provided which may further enhance the thermal stability of the PCD element.

Furthermore, the PCD body in the structure of Figure 1 comprising a PCD structure bonded to a cemented carbide support body may be created or finished by, for example, grinding, to provide a PCD element which is substantially cylindrical and having a substantially planar working surface, or a generally domed, pointed, rounded conical or frusto-conical working surface. The PCD element may be suitable for use in, for example, a rotary shear (or drag) bit for boring into the earth, for a percussion drill bit or for a pick for mining or asphalt degradation.

Versions are described in more detail below with reference to the following examples which are provided herein by way of illustration only and are not intended to be limiting.

Example 1

As shown in Figure 3, a precomposite for forming an example PCD construction having 5 vol% binder in the PCD construction was prepared by placing 1.36g of diamond powder 40 having an average grain size of around 4 microns into a niobium canister 42 and a powder bed 44 of 0.24g of cobalt binder was placed on top of the diamond powder. The powder 44 was covered with another layer of niobium cup 46 and a pre-formed sustrate 48 was inserted into the further niobium cup 46, this cup assisting in inhibiting infiltration of binder from the substrate into the PCD during sintering.

The pre-composite was then loaded into a press assembly subjected to an ultra-high pressure of at least around 6.5 GPa and temperature at which the superhard material is thermodynamically stable to sinter the superhard grains, of around 1450 deg C. In some examples the sintering time ranged from between around 60 seconds to around 30 minutes. In some examples, pressure to which the pre-composite is subjected during sintering is between around 7GPa to around 10 GPa and the temperature to which the pre-composite may be subjected is between around 1450 deg C to around 2000 deg C, particularly if lower levels of binder phase are to be achieved, for example around 3 vol%.

The process was repeated to assemble PCD constructions comprising 3vol% Co, 7 vol% Co and 9 vol% Co. The residual binder content of the PCD for a specific diamond grain size may be manipulated by the pressure and temperature conditions during sintering of the PCD in a high pressure and high temperature apparatus and, to a degree, with the admix binder levels in the green body of PCD before sintering.

Various samples of the PCD constructions prepared above were analysed by subjecting the samples to a number of tests. The results of these tests are shown in Figures 4 and 5.

The first test to which the PCD constructions comprising 3vol% Co, 5vol% Co, 7 vol% Co and 9vol% Co were subjected was a wear test using a Paarl granite test technique. The Paarl granite turning test comprises machining a bar of paarl granite with a clamped PCD construction testpiece. This is a dry test that runs for about 3 minutes. A wear scar is generated on the edge of the PCD testpiece as the workpiece and the PCD testpiece rub against each other. The granite workpiece also loses material during the operation. Wear resistance is then measured by the size of the wear scar on the PCD testpiece. The larger the wear scar, the softer the PCD material. The results of this test are shown in Figure 4. It will be seen that the wear scar in the PCD constructions comprising 3vol% and 5vol% Co have good wear resistance with a smaller wear scar than those comprising 7vollY0 and 9vol% Co. The samples were also subjected to a low energy drop test to determione the brittleness of the PCD constructions. This test comprises impacting a 10kg steel mass on to the edge of a clamped PCD testpiece. The height is set to give an energy of SJoules. Several impacts are done on the testpiece. The edge of the PCD testpiece can either remain intact or chip from the impacts. Three samples are tested at a time for a complete test. The test measures resistance of the material to edge chipping from impact. Total chip area size is measured to evaluate the extent of the chipping damage. The bigger the chip area size, the more prone to chipping is the material. The results are shown in Figure 5.

It will be seen from Figures 4 and 5 that whilst the example PCD constructions comprising 3vol% Co and 5 vol% Co are more brittle than the conventional PCD having 7 vol% co and 9 vol% Co, surprisingly, the wear resistance of the examples is significantly improved. Thus, the applicants have appreciated that the optimal range to achieve an advantageous balance between the wear resistance and brittleness of the PCD construction is to have a residual binder content in the interstitial spaces of the PCD of between around 3vol% and 5 vol%.

The percentage by volume of binder phase in a PCD constructions may be determined using conventionsl SEM Image analysis techniques is which polished samples of the PCD material to be analysed are obtained and 16 backscattered electron (BSE) images taken using, for example, a JSM7500F scanning electron microscope at 15KV. Image analysis of PCD is carried out using a BSE scanning electron microscopy image of a polished section of the sample. The BSE image gives atomic number contrast so that diamond and cobalt can be clearly differentiated by gray level differences. Image analysis software is used to calculate the percentage area of each component in the image. For example, using the commercially available Analysis (TM) 3.2 software package, an automated algorithm is applied for quantifying volume content, grain size, mean free path and diamond contiguity of the PCD sample. The procedure uses a grain separation routine provided by the Analysis (TM) software. The binder phase content is determined by measuring the areas obtained by threshholding and binarizing the analysed image in accordance with conventional image analysis techniques.

Alternatively, the amount of binder phase may be determined using a conventional ICP technique in which the PCD sample is weighed and ashed to burn off carbon. The ashed powder is weighed again and dissolved in acid which mainly dissolves the binder phase material, such as cobalt. Undissolved carbon is filtered off. The acid binder solution is diluted to a set volume. The solution is then measured for concentration of the binder using an ICP technique. From the ICP results, determination of the binder content and percentage is possible. In particular, an Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) analytical technique may be used to determine the binder content as it is a technique for the detection of trace metals. It is a type of emission spectroscopy that uses the inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element. The intensity of this emission is indicative of the concentration of the element within the sample. ICP-OES requires the sample to be in solution, and for PCD this is achieved through a combination of ashing to remove the diamond component and an acid digestion of the remaining binder elements. The resultant solution is compared against calibration standards of known concentration to determine the elemental composition of the sample.

It is paramount to engineer the binder content of PCD for specific applications whether it is purely abrasion resistance that is important or purely impact resistance that is important for the particular application, or various combinations of the two. However the present applicant has determined that there is a minimum metallic or non-metallic binder phase level in the PCD after sintering below which the PCD layer becomes too brittle to withstand loading conditions in demanding applications like oil and gas drilling and a maximum level above which it becomes too soft for demanding abrasion applications and where there is too much thermal load.

The determined optimum range of metallic or non-metallic binder phase is between around 3vol% to around 5vol% (which equates to around 7wt% to 10wt%). It has been determined that below around 7wt% the PCD layer becomes too brittle to withstand loading conditions in demanding applications like oil and gas drilling and above around 10wt% it becomes too soft for demanding abrasion applications and applications where there is too much thermal load during application.

The binder phase content of the superhard layer 2 for a specific grain size of the superhard material may be controlled by manipulating the pressure and temperature conditions during sintering of the superhard material in a high pressure and high temperature apparatus and to a degree with the admix catalyst/binder levels in the green body before sintering to achieve the desired range of binder phase mentioned above.

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

Claims

Claims: 1. A superhard polycrystalline construction comprising: a body of polycrystalline superhard material, the body of polycrystalline superhard material comprising: a superhard phase comprising interbonded grains having interstitial spaces therebetween, and a non-super hard phase dispersed in the interstitial spaces; wherein the non-super hard phase occupies between around 3 vol% to around 5 vol% of the total volume of the body of polycrystalline superhard material.
2. A superhard polycrystalline construction according to claim 1, wherein the superhard grains comprise natural and/or synthetic diamond grains, the superhard polycrystalline construction forming a polycrystalline diamond construction.
3. A superhard polycrystalline construction according to any one of the preceding claims, further comprising a non-superhard phase comprising a binder phase.
4. A superhard polycrystalline construction according to claim 3, wherein the binder phase comprises cobalt, and/or one or more other iron group elements, such as iron or nickel, or an alloy thereof, and/or one or more carbides, nitrides, borides, and oxides of the metals of Groups IV-VI in the periodic table.
5. A superhard polycrystalline construction according to any one of the preceding claims, further comprising a cemented carbide substrate bonded to the body of polycrystalline material along an interface.
6. A superhard polycrystalline construction according to claim 5, wherein the cemented carbide substrate comprises tungsten carbide particles bonded together by a binder material, the binder material comprising an alloy of Co, Ni and Cr.
7. A superhard polycrystalline construction according to any one of claims 5 or 6, wherein the cemented carbide substrate comprises between around 8 to 13 weight or volume % binder material.
8. A superhard polycrystalline construction according to any one of the preceding claims, wherein the binder phase comprises a non-metallic material.
9. A superhard polycrystalline construction according to any one of claims 1 to 7 wherein the binder phase comprises a metallic material.
10. A superhard polycrystalline construction for a rotary shear bit for boring into the earth, or for a percussion drill bit, comprising a superhard polycrystalline construction as claimed in any one of the preceding claims bonded to a cemented carbide support body.
11. A superhard polycrystalline construction according to any one of the preceding claims, wherein the second phase particles or granules have a different stiffness and/or fracture toughness than that of the superhard phase.
12. A method of forming the superhard polycrystalline construction of any one of the preceding claims.
13. A tool comprising a superhard polycrystalline construction according to any one of claims 1 to 11, the tool being for cutting, milling, grinding, drilling, earth boring, rock drilling or other abrasive applications.
14. A tool according to claim 13, wherein the tool comprises a drill bit for earth boring or rock drilling.
15. A tool according to claim 13, wherein the tool comprises a rotary fixed-cutter bit for use in the oil and gas drilling industry.
16. A tool according to claim 13, wherein the tool is a rolling cone drill bit, a hole opening tool, an expandable tool, a reamer or other earth boring tools.
17. A drill bit or a cutter or a component therefor comprising the superhard polycrystalline construction according to any one of claims 1 to 11.
18. A superhard polycrystalline construction substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings.
19. A method of making a super hard polycrystalline construction, substantially as hereinbefore described with reference to any one embodiment as that embodiment is illustrated in the accompanying drawings.