Field

This disclosure relates to polycrystalline diamond (PCD) constructions, a method for making same and tools comprising same, particularly but not exclusively for use in rock degradation or drilling, or for boring into the earth.

Background

PCD material comprises a mass of substantially inter-grown diamond grains and interstices between the diamond grains. PCD material may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature in the presence of a sintering aid such as cobalt, which may promote the inter-growth of the diamond grains. The sintering aid may also be referred to as a catalyst material for diamond. Interstices within the PCD material may be wholly or partially filled with residual catalyst material after the material is formed by a sintering process. PCD material may be integrally formed on and bonded to a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for sintering the PCD material. Tool inserts comprising PCD material are widely used in drill bits for boring into the earth in the oil and gas drilling industry. Although PCD material is extremely abrasion resistant, there is a need for PCD tool inserts that have enhanced fracture resistance.

Summary

Viewed from a first aspect there is provided a polycrystalline diamond (PCD) construction comprising: a first region comprising: a first set of one or more strata comprising a first grade of PCD material; and a second set of strata comprising a second grade of PCD material, the first set of strata being arranged in an alternating configuration with the second set of strata, the alternating strata being bonded to each other by direct inter-growth of diamond grains to form an integral stratified PCD structure, the strata in the first set having a greater average thickness than the strata in the second set; wherein: the first grade of PCD material differs from the second grade of PCD material in one or more of diamond and metal network compositional ratio, metal elemental composition, or average diamond grain size; one or more of the strata in the first set comprising: a smaller average diamond grain size than one or more strata in the second region, and/or a greater volume percentage of residual catalyst/binder in interstitial spaces between interbonded diamond grains than one or more strata in the second region.

Viewed from a second aspect there is provided a method of making a PCD construction, the method comprising providing a first plurality of aggregate masses comprising diamond grains having a first average grain size, at least one second aggregate mass comprising diamond grains having a second average size greater than said first average grain size; arranging the first and second aggregate masses in an alternating configuration to form a pre-sinter assembly; and treating the pre-sinter assembly in the presence of a catalyst material for diamond at an ultra-high pressure and high temperature at which diamond is more thermodynamically stable than graphite to sinter together the diamond grains and form an integral PCD construction comprising: a first region comprising: a first set of one or more strata formed from the first plurality of aggregate masses; and a second set of strata formed from the second plurality of aggregate masses, the first set of strata being arranged in an alternating configuration with the second set of strata, the alternating strata being bonded to each other by direct inter-growth of diamond grains to form an integral stratified PCD structure, the strata in the first set having a greater average thickness than the strata in the second set; wherein: the material of the first strata differs from the material of the second strata in one or more of diamond and metal network compositional ratio, metal elemental composition, or average diamond grain size; one or more of the strata in the first set comprising: a smaller average diamond grain size than one or more strata in the second region, and/or a greater volume percentage of residual catalyst/binder in interstitial spaces between interbonded diamond grains than one or more strata in the second region.

A PCD element comprising a PCD structure bonded to a cemented carbide support body can be provided. A tool comprising a PCD element can also be provided. The tool may be a drill bit or a component of a drill bit for boring into the earth, or a pick or an anvil for degrading or breaking hard material such as asphalt or rock. Brief introduction to the drawings

Examples of PCD constructions will now be described with reference to the accompanying drawings, in which:

FIG 1 is a schematic 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 a conventional portion of a PCD micro-structure with interstices between the inter-bonded diamond grains filled with a non-diamond phase material;

FIG 3 is a schematic longitudinal cross-section view of an example of a PCD cutter element according to a first example;

FIG 4 is a schematic longitudinal cross-section view of an example of a PCD cutter element according to a second example; and

FIG 5 is a schematic longitudinal cross-section view of an example of a PCD cutter element according to a third example.

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

Description

As used herein, polycrystalline diamond (PCD) is a super-hard material comprising a mass of diamond grains, a substantial portion of which are directly inter-bonded (intergrown) with each other and in which the content of diamond is at least about 80 volume percent of the material.

As used herein,“interstices” or“interstitial regions” are regions between the interbonded diamond grains in the 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. 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. Further 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.

As used herein, a catalyst material for diamond is a material capable of promoting the direct intergrowth of diamond grains.

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.

Different PCD grades may have different microstructure 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.

The table below shows approximate compositional characteristics and properties of three example PCD grades referred to as PCD grades I, II and III. All of the PCD grades in the table below comprise interstitial regions filled with material comprising cobalt metal, which is an example of catalyst material for diamond.

With reference to Figure 1 , a conventional PCD construction 1 is shown which is suitable for use as a cutter insert for a drill bit (not shown) for boring into the earth. The construction 1 comprises a PCD structure 2 bonded or otherwise joined to a support body or substrate 3 along an interface 8 which may be substantially planar or non-planar.

The PCD structure 2 comprises a body of super hard material such as PCD material, which may conventionally comprise one or more PCD grades. The substrate 3 may be formed of a hard material such as a cemented carbide material and may be, for example, cemented tungsten carbide, cemented tantalum carbide, cemented titanium carbide, cemented molybdenum carbide or mixtures thereof. The binder metal for such carbides may be, for example, nickel, cobalt, iron or an alloy containing one or more of these metals. Typically, this binder will be present in an amount of 10 to 20 mass %, but this may be as low as 6 mass % or less. Some of the binder metal may infiltrate the body of polycrystalline diamond material 2 during formation of the compact 1.

The construction 1 may form a cutting element which may be mounted in use into a bit body such as a drag bit body (not shown). The exposed top surface 4 of the super hard material 2 opposite the substrate 3 forms the working surface, which is the surface which, along with its edge 6, performs the cutting in use.

The substrate 3 may be, for example, generally cylindrical and has a peripheral surface 10 and a peripheral top edge 8.

The PCD element 1 may also be substantially cylindrical in shape, with the PCD structure 2 located at a working end and defining the working surface 4.

The exposed surface 4 of the cutter element 1 comprises the working surface 4 which also acts as a rake face in use. A chamfer may extend between the working surface 4 and the cutting edge 6, and at least a part of a flank or barrel of the cutter, the cutting edge 6 being defined by the edge of the chamfer and the flank.

The working surface or“rake face” 4 of the cutter 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 referred to as the top face or working surface of the cutter. As used herein,“chips” are the pieces of a body removed from the work surface of the body by the cutter in use.

As used herein, the“flank” 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 may provide a clearance from the body and may comprise more than one flank face. As used herein, a“cutting edge” 6 is intended to perform cutting of a body in use.

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 be progressively 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. As used herein, it is understood that the term“cutting edge” 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.

As used herein, the term“stress state” refers to a compressive, unstressed or tensile stress state. Compressive and tensile stress states are understood to be opposite stress states from each other. In a cylindrical geometrical system, the stress states may be axial, radial or circumferential, or a net stress state.

As shown in Figure 2, during formation of the polycrystalline composite construction 1 , the interstices 24 between the diamond grains 22 forming the PCD material 2, 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 and may also, or in place of, include one or more other non-super hard phase additions.

With reference to Figures 1 and 2, the substrate 3 may comprise a cemented carbide material, such as tungsten carbide (WC) formed of 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. With reference to Figure 3, an example of a PCD construction comprises a PCD structure 2 integrally joined to a cemented carbide support body 3. The PCD structure 2 comprises a first region 30 formed of a plurality of second regions 32 in the form of alternating (or inter-leaved) strata or layers, said second regions being interleaved with (alternating with) a plurality of third regions 34 also in the form of alternating (or inter-leaved) strata or layers.

In the example shown in Figure 3, the layers 32 and 34 forming the second and third regions respectively are shown to extend in a plane substantially parallel with the plane through the longitudinal axis of the construction and extend to and form part of the working surface 4 of the PCD structure 2. In this example, the layers 32 and 34 do not extend to the interface 8 with the substrate 3 but are spaced from the interface 8 and from the peripheral side edge of the construction by a further region 36 of PCD material.

The material of the alternating layers 32 forming the second region differ in one or more of diamond and metal network compositional ratio, or metal elemental composition, diamond grain size distribution, or residual stress state to the material or materials of the alternating layers 34 forming the third region and have a radial thickness that is smaller than the radial thickness of the layers 34 forming the third region. In some examples, the average size of the diamond grains in the PCD material of the thinner layers 32 is greater than the average grain size of the diamond grains in the PCD material of the thicker layers 34 of the third region. In a further example, the volume percentage of residual binder/catalyst material in the interstitial spaces between the interbonded diamond grains in the PCD material of the thinner layers 32 is less than the volume percentage of residual binder/catalyst material in the interstitial spaces between the interbonded diamond grains in the PCD material of the thicker layers 34 of the third region.

The example of Figure 4 differs from that of Figure 3 in that the first region 30 comprising the alternating layers of the second and third regions 32 and 34, is spaced from the working face 4 by the region 36 of PCD material that separates the first region 30 from the interface 8 and peripheral side edge of the construction 2.

Figure 5 is an example in which the construction differs from that of Figure 3 in that the alternating layers forming the first region 30 are oriented to extend in a plane substantially perpendicular to the plane through which the longitudinal axis of the construction extends. In this example, the layers 32 and 34 have respective thicknesses in the longitudinal plane, the individual thicknesses of the layers 32 in the second region being less than the thicknesses of the individual layers 34 in the third region.

The thicknesses of the individual layers 32 and 34 may, for example, be in the range of about 50 microns to about 300 microns and may be arranged substantially parallel to the working surface 4 of the PCD structure 2, substantially perpendicular to the working surface 4, or at an angle thereto, thereby extending in any orientation relative thereto such that the strata 32, 34 may be inclined away from the working surface 4 and cutting edge 6 of the PCD structure 2.

As shown in the example of Figures 3 and 4, the strata 32, 34 may be generally annular or part annular and substantially concentric with a substantially cylindrical side surface 10 of the construction 1.

The PCD material forming the substantially annular region 36 extending around the first region 30 may differ from the PCD materials of the second and/or third regions 32 and 34 in one or more of diamond and metal network compositional ratio, metal elemental composition, or diamond grain size distribution.

The PCD material for any one or more of the second and third regions 32, 34 and region 36 may be selected to achieve the desired configuration such as a tensioned region between two compressed regions. For example, variations in mechanical properties such as density, elastic modulus, hardness and coefficient of thermal expansion (CTE) may be selected for this purpose. Such variations may be achieved by means of variations in content of diamond grains, content and type of filler material, size distribution or average grain size of the PCD grains.

In some examples, the layers 32, 34 may be curved or bowed, and, in some examples, may intersect a side surface 27 of the PCD structure, in addition to or instead of intersecting the working surface 4.

An example method for making a PCD construction is now described. Aggregate masses in the form of sheets containing diamond grains held together by a binder material may be provided. The sheets may be made by a method known in the art, such as by extrusion or tape casting methods, in which slurries comprising diamond grains having respective size distributions suitable for making the desired respective PCD grades, and a binder material is spread onto a surface and allowed to dry. Other methods for making diamond-containing sheets may also be used, such as described in United States patents numbers 5,766,394 and 6,446,740. Alternative methods for depositing diamond-bearing layers include spraying methods, such as thermal spraying. The binder material may comprise a water-based organic binder such as methyl cellulose or polyethylene glycol (PEG) and different sheets comprising diamond grains having different size distributions, diamond content or additives may be provided. For example, at least two sheets comprising diamond having different average diamond grain sizes may be provided and first and second sets of discs may be cut from the respective first and second sheets. The sheets may also contain catalyst material for diamond, such as cobalt, and / or additives for inhibiting abnormal growth of the diamond grains or enhancing the properties of the PCD material. For example, the sheets may contain about 0.5 weight percent to about 5 weight percent of vanadium carbide, chromium carbide or tungsten carbide. In one example, each of the sets may comprise about 10 to 20 discs. A support body comprising cemented carbide in which the cement or binder material comprises a catalyst material for diamond, such as cobalt, may be provided. The support body may have a non-planar end or a substantially planar proximate end on which the PCD structure is to be formed. A non- planar shape of the end may be configured to reduce undesirable residual stress between the PCD structure and the support body. A cup may be provided for use in assembling the diamond-containing sheets onto the support body. The first and second sets of discs may be stacked into the bottom of the cup in alternating order. In one version of the method, a layer of substantially loose diamond grains may be packed onto the uppermost of the discs. The support body may then be inserted into the cup with the proximate end going in first and pushed against the substantially loose diamond grains, causing them to move slightly and position themselves according to the shape of the non-planar end of the support body to form a pre-sinter assembly.

The pre-sinter assembly can be placed into a capsule for an ultra-high pressure press and subjected to an ultra-high pressure of at least about 5.5 GPa and a high temperature of at least about 1 ,300 degrees centigrade to sinter the diamond grains and form a PCD element comprising a PCD structure integrally joined to the support body. In one version of the method, when the pre-sinter assembly is treated at the ultra-high pressure and high temperature, the binder material within the support body melts and infiltrates the strata of diamond grains. The presence of the molten catalyst material from the support body is likely to promote the sintering of the diamond grains by intergrowth with each other to form an integral, stratified PCD structure.

In some versions of the method, the aggregate masses may comprise substantially loose diamond grains, or diamond grains held together by a binder material. The aggregate masses may be in the form of granules, discs, wafers or sheets, and may contain catalyst material for diamond and / or additives for reducing abnormal diamond grain growth, for example, or the aggregated mass may be substantially free of catalyst material or additives. In one version, the first mean size may be in the range from about 0.1 micron to about 15 microns, and the second mean size may be in the range from about 10 microns to about 40 microns. In one version, the aggregate masses may be assembled onto a cemented carbide support body.

The pre-sinter assembly for making an example PCD construction may comprise a support body to form the substrate 3, a region comprising diamond grains to form the region 36 packed against a non-planar end of the support body, and a plurality of alternating diamond-containing aggregate masses in the general form of discs or wafers to form the alternating layers 32, 34 stacked on the region to form the region 36 adjacent the substrate. In some versions, the aggregate masses may be in the form of loose diamond grains or granules. The pre-sinter assembly may be heated to remove the binder material comprised in the stacked discs.

The plurality of alternating strata 32, 34 may be formed of different respective grades of PCD material, that is, diamond grains having differing average grain sizes and/or differing binder/catalyst volume percentage composition. The portion 36 may be cooperatively formed according to the shape of the non- planar interface 8 of the support body 3 to which it has integrally bonded during the treatment at the ultra-high pressure, in the examples where the interface is substantially non planar. The alternating strata 32, 34 are bonded together by direct diamond-to-diamond intergrowth to form an integral, solid and stratified PCD region 30. The shapes of the PCD strata 32, 34 may be curved, bowed or distorted in some way as a result of being subjected to the ultra-high pressure. In some versions of the method, the aggregate masses may be arranged in the pre-sinter assembly to achieve various other configurations of strata within the PCD structure, taking into account possible distortion of the arrangement during the ultra-high pressure and high temperature treatment. As the strata 32, 34 may comprise different respective PCD grades as a result of the different average diamond grain sizes of the strata, different amounts of catalyst material may infiltrate into the strata due to the different sizes of spaces between the diamond grains. The corresponding alternating PCD strata 32, 34 may thus comprise different, alternating amounts of residual catalyst/bi nder material for diamond. The content of the filler material in terms of volume percent within the thicker strata 34 may be greater than that within each of the thinner strata 32.

In one example, the strata 32 may comprise diamond grains having mean size greater than the mean size of the diamond grains of the strata 34.

While wishing not to be bound by a particular theory, when the stratified PCD structure is allowed to cool from the high temperature at which it was formed, the alternating strata containing different amounts of metal catalyst material may contract at different rates. This may be because metal contracts much more substantially than diamond does as it cools from a high temperature. This differential rate of contraction may cause adjacent strata to pull against each other, thus inducing opposing stresses in them.

The PCD constructions described with reference to Figures 3 to 5 may be processed by grinding to modify its shape to form a PCD construction substantially as described with reference to Figure 1. This may involve removing part of some of the strata 32, 34 to form a substantially planar working surface and a substantially cylindrical side surface. 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 achieved 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 2, may thus be provided. In one example, the substantially porous region may comprise at most 2 weight percent of catalyst material.

Each stratum or layer may have a thickness of at least about 50 microns, at least about 100 microns, or at least about 200 microns. Each stratum or layer may have a thickness of at most about 500 microns. In some examples, each stratum or layer may have a thickness of at least about 0.05 percent, at least about 0.5 percent, at least about 1 percent or at least about 2 percent of a thickness of the PCD structure measured from a point on a working surface at one end to a point on an opposing surface. In some examples, each stratum or layer may have a thickness of at most about 5 percent of the thickness of the PCD structure.

As used herein, the term“residual stress state” refers to the stress state of a body or part of a body in the absence of an externally-applied loading force. The residual stress state of a PCD structure, including a layer structure may be measured by means of a strain gauge and progressively removing material layer by layer. In some examples of PCD elements, at least one compressed region may have a compressive residual stress of at least about 50 MPa, at least about 100 MPa, at least about 200 MPa, at least about 400 MPa or even at least about 600 MPa. The difference between the magnitude of the residual stress of adjacent strata may be at least about 50 MPa, at least about 100 MPa, at least about 200 MPa, at least about 400 MPa, at least about 600 MPa, at least about 800 MPa or even at least about 1 ,000 MPa. In one example, at least two successive compressed regions or tensioned regions may have different residual stresses.

While the provision of a PCD structure with PCD strata having alternating compression and tensile stress states tends to increase the overall effective toughness of the PCD structure, this may have the effect of increasing the potential incidence of de-lamination, in which the strata may tend to come apart. While wishing not to be bound by a particular theory, de-lamination may tend to arise if the PCD strata are not sufficiently strong to sustain the residual stress between them. This effect may be ameliorated by selecting the PCD grades to have sufficiently high TRS. The TRS of the PCD grade or grades of which the tensioned region is formed should be greater than the residual tension that it may experience. One way of influencing the magnitude of the stress that a region may experience is by selecting the relative thicknesses of adjacent regions.

The PCD construction 1 may be substantially cylindrical and have a substantially planar working surface (as shown in Figures 3 to 5), or a generally domed, pointed, rounded conical or frusto-conical working surface. The PCD element may be for 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.

PCD elements as described herein may have enhanced resistance to fracture.

A non-limiting example PCD element comprising alternating strata of two different grades of PCD was provided as follows.

First and second sheets, each containing diamond grains having a different mean size and held together by an organic binder were made by the tape casting method. This method involved providing respective slurries of diamond grains suspended in liquid binder, casting the slurries into sheet form and allowing them to dry to form self-supportable diamond-containing sheets. The mean size of the diamond grains within the first sheet was in the range from about 5 microns to about 14 microns, and the mean size of the diamond grains within the second sheet was in the range from about 18 microns to about 25 microns. Both sheets also contained about 3 weight percent vanadium carbide and about 1 weight percent cobalt. After drying, the sheets were about 0.12 mm thick. Fifteen circular discs having diameter of about 13 mm were cut from each of the sheets to provide first and seconds sets of disc shaped wafers. A support body formed of cobalt-cemented tungsten carbide was provided. The support body was generally cylindrical in shape, having a diameter of about 13 mm and a non-planar end formed with a central projecting member. A metal cup having an inner diameter of about 13 mm was provided for assembling a pre-sinter assembly. The diamond-containing wafers were placed into the cup, alternately stacked on top of each other with discs from the first and second sets inter-leaved. A layer of loose diamond grains having a mean size in the range from about 18 microns to about 25 microns was placed into the upturned cup, on top of the uppermost of the wafers, and the support body was inserted into the cup, with the non-planar end pushed against the layer.

The pre-sinter assembly thus formed was assembled into a capsule for an ultra-high pressure press and subjected to a pressure of about 6.8 GPa and a temperature of at least about 1 ,450 degrees centigrade for about 10 minutes to sinter the diamond grains and form a PCD element comprising a PCD structure bonded to the support body.

The PCD element was processed by grinding and lapping to form a cutter element having a substantially planar working surface and cylindrical side, and a 45 degree chamfer between the working surface and the side. The cutter element was subjected to a turret milling test in which it was used to cut a body of granite until the PCD structure fractured or became so badly worn that effective cutting could no longer be achieved. At various intervals, the test was paused to examine the cutter element and measure the size of the wear scar that had formed into PCD structure as a result of the cutting. The example PCD cutter exhibited better wear resistance and fracture resistance that would be expected from a PCD material having the aggregate, non- stratified microstructure and properties of the component grades.

Whilst not wishing to be bound by a particular theory, it is believed that the example PCD constructions may be manufactured with alternating layers of two distinct PCD feeds (either in the horizontal, vertical, or other directions) with the intent that any crack that is initiated may be terminated by intersecting a PCD feed with different properties, or be directed between the layers due to residual stress differences between the layers to avoid a catastrophic spall. In the examples where the alternating layers do not extend all the way out to the outer surface of the cutter, but rather are spaced therefrom by a ring of solid PCD, it may be possible to contain/control the different generated residual stresses within the layers by using PCD with different properties, generating tension and compression as desired, and inhibit these stresses from extending out to the peripheral outer surface of the construction thereby enabling management of crack initiation and propagation during use of the construction.