POLYCRYSTALLINE DIAMOND COMPOSITE COMPACT

Field

The invention relates to polycrystalline diamond (PCD) composite compact elements comprising a PCD structure  particularly but not exclusively for a rock boring tool  and to tools comprising the elements.

Background

Polycrystalline diamond (PCD) is a super-hard  also known as superabrasive material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. A material wholly or partly filling the interstices may be referred to as filler material. PCD may be formed in the presence of a sintering aid such as cobalt  which is capable of promoting the inter-growth of diamond grains. The sintering aid may be referred to as a solvent / catalyst material for diamond  owing to its function of dissolving diamond to some extent and catalyst 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. PCD may be formed on a cobalt-cemented tungsten carbide substrate  which may provide a source of cobalt solvent / catalyst for the PCD.

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. For example  PCD elements may be used as cutting elements on drill bits used for boring into the earth in the oil and gas drilling industry. In many of these applications the temperature of the PCD material may become elevated as it engages a rock formation  workpiece or body with high energy. Unfortunately  mechanical properties of PCD such as hardness and strength tend to deteriorate at high temperatures  largely as a result of residual solvent / catalyst material dispersed within it.

PCT patent publication number WO9929465 discusses that drilling hard rock and dealing with high well bore temperature gradients have been persistent problems in the drilling industry. The then current state-of-the-art TSP diamond cutter attachment procedure is to braze thermally stable polycrystalline diamond (TSP diamond) to carbide substrates. However  TSP brazing methods using TiCuSil alloy result in an undesirable discontinuous layer of TiC adjacent to the TSP diamond surface. Maximum strength properties are not realized unless a thin continuous layer of reaction product forms on the TSP surface (i.e. unless wetting is complete).

United States patent number 7 377 341 discusses that a PCD body that is substantially free of the solvent catalyst material is precluded from subsequent attachment to a metallic substrate by brazing or other similar bonding operation. The attachment of such substrates to the PCD body is highly desired to provide a PCD compact element that can be readily adapted for use in many desirable applications. However  it is very difficult to bond the thermally stable PCD body to conventionally used substrates. Since conventionally formed thermally stable PCD bodies are devoid of a metallic substrate  they cannot be attached to a drill bit by conventional brazing process. Rather  the use of such a thermally stable PCD body in drilling application requires that the PCD body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit  which is labour intensive  time consuming  and which does not provide a most secure method of attachment.

United States patent number 7 435 377 discusses that polycrystalline diamond (PCD) and other ultra-hard materials may be joined to a supporting mass by means of brazing. However  a disadvantage of brazing is relates to concerns over potential heat damage of the PCD product  which has been a limiting factor in the past.

United States patent number 7 487 849 discusses that because TSP (thermally stable product) is made by removing cobalt from a diamond layer  attachment of TSP to a substrate is significantly more complicated  as compared to the attachment of PDC to a substrate.

United States patent number 7 533 740 discloses a cutting element comprising TSP material bonded to a tungsten carbide substrate by brazing (this patent uses the term “TSP” as described in United States patents numbers 7 234 550 and 7 426 696  which use the term “TSP” to mean “thermally stable product”  including both partially and completely leached polycrystalline diamond compounds).

United States patent publication number 2008/0085407 discloses a super-abrasive compact element wherein a super-abrasive volume including a tungsten carbide layer may be brazed  soldered  welded (including frictional or inertial welding)  or otherwise affixed to a substrate.

There is a need for PCD composite compact elements  particularly thermally stable PCD elements  having superior mechanical properties.

Summary

An aspect of the invention provides a polycrystalline diamond (PCD) composite compact element comprising a substrate  a PCD structure bonded to the substrate  and a bond material bonding the PCD structure to the substrate; the PCD structure being thermally stable and having a mean Young’s modulus of at least about 800 GPa  at least about 850 GPa  or at least 870 GPa  the PCD structure having an interstitial mean free path of at least about 0.05 microns and at most about 1.5 microns; the standard deviation of the mean free path being at least about 0.05 microns and at most about 1.5 microns.

An embodiment of the invention provides a PCD composite compact element comprising a PCD structure bonded to a substrate by means of a bond material; the PCD structure being thermally stable and having a mean Young’s modulus of at least about 800 GPa  at least about 850 GPa  or at least 870 GPa  and a mean diamond grain contiguity greater than about 60 percent or greater than 60.5 percent.

In one embodiment of the invention  the bond material may comprise an epoxy material for joining ceramic materials.

In one embodiment of the invention  the PCD structure may be brazed to the substrate  the bond material being a braze alloy in the form of a braze layer between the PCD structure and the substrate.

In one embodiment of the invention  the braze alloy may have a melting onset temperature  at which the alloy begins to melt  of at most about 1 050 degrees centigrade  at most about 950 degrees centigrade  at most about 900 degrees centigrade or even at most about 850 degrees centigrade  and may contain at least one element selected from the group consisting of Ti  V  Cr  Mn  Zr  Nb  Mo  Hf  Ta  W and Re. In some embodiments  the braze alloy may contain Ti and Ag  or Ti and Cu.

An aspect of the invention provides a PCD composite compact element comprising a PCD structure bonded to a substrate by means of a braze layer comprising braze material; the PCD structure being thermally stable and containing braze material.

In some embodiments of the invention  the PCD structure may contain braze alloy material within pores  crevices or irregularities formed at a boundary of the PCD structure. In one embodiment  pores  crevices or irregularities may formed at a boundary of the PCD structure by removing filler material from between diamond grains  such as by means of acid treatment.

In some embodiments of the invention  the PCD structure may have a mean Young’s modulus of at least about 800 GPa  at least about 850 GPa  or at least 870 GPa.

In one embodiment of the invention  the PCD structure may contain braze alloy material to a depth of at least about 2 microns from an interface or boundary  such as an interface with the braze layer or with the substrate. In some embodiments of the invention  the PCD structure may contain braze material to a depth from an interface with the braze layer  the depth being in the range from about 2 microns to about 1 000 microns  in the range from about 2 microns to about 25 micron  or in the range from about 5 microns to about 15 microns. In one embodiment  the PCD structure may contain braze material substantially throughout the whole of the PCD structure.

In some embodiments of the invention  the PCD structure may have an interstitial mean free path in the range from about 0.05 micron to about 1.3 microns  in the range from about 0.1 micron to about 1 micron  or in the range from about 0.5 micrometers to about 1 micron; and the standard deviation of the mean free path may be in the range from about 0.05 micron to about 1.5 microns  or in the range from about 0.2 micron to about 1 micron.

In some embodiments of the invention  the PCD structure may have a mean diamond grain contiguity of at least about 60 percent  in the range from 60.5 percent to about 80 percent  in the range from 60.5 percent to about 77 percent  or in the range from 61.5 percent to about 77 percent. In one embodiment of the invention  the PCD structure may have a mean diamond grain contiguity of at most about 80 percent.

In some embodiments of the invention  the PCD structure may have a transverse rupture strength of at least about 900 MPa  at least about 950 MPa  at least about 1 000 MPa  at least about 1 050 MPa  or even at least about 1 100 MPa.

In some embodiments of the invention  the substrate may be formed of cemented carbide  such as cobalt-cemented tungsten carbide  or the substrate may comprise PCD material  or the substrate may be a composite compact element comprising cemented carbide and PCD material. In one embodiment of the invention  the PCD structure may be brazed to a further PCD structure  and in one embodiment  the PCD structure may be more thermally stable than the further PCD structure.

In some embodiments of the invention  the substrate may include superhard particles such as diamond particles dispersed within it. In one embodiment  the substrate may include diamond particles  the content of which may be in the range from about 20 volume percent to about 60 volume percent.

In some embodiments of the invention  the PCD structure may exhibit no substantial structural degradation or deterioration of hardness or abrasion resistance after exposure to a temperature above about 400 degrees centigrade or in the range from about 750 degrees centigrade to about 800 degrees centigrade  or even in the range from about 760 degrees centigrade to about 810 degrees centigrade.

In one embodiment  the PCD structure may be substantially free of material capable of functioning as solvent / catalyst for diamond. In some embodiments  there may be less than about 5 volume percent  less than about 2 volume percent  less than about 1 volume percent or less than about 0.5 volume percent of solvent / catalyst for diamond in the PCD structure. In some embodiments  the PCD structure may be at least partially porous  or substantially the entire PCD structure may be porous.

In some embodiments of the invention  the PCD structure may have an oxidation onset temperature of at least about 800 degrees centigrade  at least about 900 degrees centigrade or even at least about 950 degree centigrade.

In some embodiments of the invention  the PCD structure may not be substantially entirely porous and may have a mean Young’s modulus of at least about 900 GPa  at least about 950 GPa  at least about 1 000 GPa; and the transverse rupture strength is at least about 1 000 MPa  at least about 1 100 Mpa  at least about 1 400 MPa  at least about 1 500 MPa  or even at least about 1 600 MPa. .

In one embodiment of the invention  PCD structure may include a filler material comprising a ternary carbide of the general formula: Mx M""y Cz wherein; M is at least one metal selected from the group consisting of the transition metals and the rare earth metals; M"" is a metal selected from the group consisting of the main group metals or metalloid elements and the transition metals Zn and Cd; x is from 2.5 to 5.0; y is from 0.5 to 3.0; and z is from 0.1 to 1.2.

In some embodiments  the PCD structure may include a filler material comprising a tin- based inter-metallic or ternary carbide compound formed with a metallic solvent / catalyst for diamond. In one embodiment  the metallic solvent / catalyst material for diamond may comprise cobalt.

In one embodiment of the invention  the shear strength of the bond between the PCD structure and the substrate may be greater than about 100 MPa. In some embodiments  the shear strength of the bond between the PCD structure and the substrate may be in the range from about 100 MPa to about 500 MPa  in the range from about 100 MPa to about 300 MPa  or in the range from about 200 MPa to about 300 MPa.

In some embodiments of the invention  the PCD structure may comprise at least about 90 volume percent inter-bonded diamond grains having a mean size in the range from about 0.1 microns to 25 microns  in the range from about 0.1 micron to 20 microns  in the range from about 0.1 micron to about 15 microns  in the range from about 0.1 microns to about 10 microns  or in the range from about 0.1 micron to about 7 micron. In one embodiment  the PCD structure may comprise a diamond content in the range from about 90 to about 99 volume percent of the PCD structure  and in one embodiment  the PCD structure may comprise at least 92 volume percent diamond.

In one embodiment of the invention  the PCD structure may comprise diamond grains having a multi-modal size distribution. In some embodiments  the PCD structure may comprise bonded diamond grains having the size distribution characteristic that at least about 50 percent of the grains have mean size greater than about 5 microns  and at least about 20 percent of the grains have mean size in the range from about 10 to about 15 microns.

In some embodiments of the invention  the PCD structure may be made by a method including forming a plurality of diamond grains into an aggregated mass and sintering them in the presence of a solvent / catalyst material for diamond  the sintering including subjecting the aggregated mass and the solvent / catalyst material to a temperature sufficiently high for the solvent / catalyst to melt and to a pressure of greater than 6.0 GPa  at least 6.2 GPa  at least about 6.5 GPa  at least about 7 GPa or at least about 8 GPa.

In some embodiments of the invention  the PCD structure may comprise at least two portions  each portion being formed of PCD material having different microstructure  composition or diamond particle size distribution  or combination of these  and different properties  such as strength or Young’s modulus. In some embodiments  at least one portion may comprise diamond particles having a multi-modal size distribution with mean particle size in the range from about 5 microns to about 20 microns  or in the range from about 5 microns to 15 about microns.

In one embodiment of the invention  the PCD composite compact element may be suitable for a drill bit for boring into the earth  such as a rotary shear-cutting bit for use in the oil and gas drilling industry. In one embodiment  the PCD composite compact element may comprise a cutting element for a rolling cone  hole opening tool  expandable tool  reamer or other earth boring tools.

An aspect of the invention provides a polycrystalline diamond (PCD) composite compact element  comprising a PCD structure bonded to a substrate; the PCD structure being substantially free of material capable of functioning as solvent / catalyst for diamond and having a mean Young’s modulus of at least about 800 GPa  at least about 850 GPa  or at least about 870 GPa.

An aspect of the invention provides a tool comprising an embodiment of a PCD composite compact element according to the invention  the tool being for cutting  milling  grinding  drilling  earth boring  rock drilling or other abrasive applications  such as the cutting and machining of metal.

A method of making an embodiment of a PCD composite compact element according to the invention is provided  the method including providing a PCD structure  treating the PCD structure to remove filler material from between diamond grains and create pores  crevices or irregularities at a boundary of the PCD structure; and brazing the PCD structure to a substrate at the boundary. The method is an aspect of the invention.

In one version of the method  pores  crevices or irregularities may be formed on a surface of the PCD structure by means of treating the PCD structure with acid. In one embodiment  the pores  crevices or irregularities may have a mean size substantially the same as the mean size of the interstices between the diamond grains  and in some embodiments  the mean size may be at least about 2 microns or at least about 5 microns  and at most about 10 microns.

Drawings

Non-limiting embodiments will now be described with reference to the accompanying drawings of which:

FIG 1A shows a schematic perspective view of an embodiment of a PCD composite compact element  and FIG 1B shows schematic longitudinal cross-section view of the embodiment of the PCD composite compact element shown in FIG 1A.

FIG 2  FIG 3  FIG 4  FIG 5 and FIG 6 show drawings of schematic longitudinal cross-section views of embodiments of PCD composite compact elements.

FIG 7 shows a perspective view of a rotary drill bit for boring into the earth.

FIG 8 shows an image of a PCD polished section  showing calculated lines indicating diamond-to-diamond contact.

FIG 9  FIG 10 and FIG 11 show graphs of number of grains versus grain size for examples of multimodal size distributions of the diamond grains within embodiments of polycrystalline diamond structures.

FIG 12 shows a schematic side view of an apparatus for measuring the transverse rupture strength of a specimen.

The same reference numbers refer to the same features in all drawings.

Detailed description of embodiments

As used herein  a “catalyst material for diamond”  also referred to as “solvent / catalyst for diamond”  is a material that is capable of promoting the nucleation  growth or inter-bonding of diamond grains at a pressure and temperature at which diamond is thermodynamically stable. Catalyst materials for diamond may be metallic  such as cobalt  iron  nickel  manganese and alloys of these  or non-metallic.

As used herein  “polycrystalline diamond” (PCD) material comprises a mass of diamond grains  a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume percent of the material. In one embodiment of PCD material  interstices between the diamond gains may be at least partly filled with a binder material comprising a catalyst for diamond. As used herein  “interstices” or “interstitial regions” are regions between the diamond grains of PCD material. In embodiments of PCD material  interstices or interstitial regions may be substantially or partially filled with a material other than diamond  or they may be substantially empty. As used herein  a “filler” material is a material that wholly or partially fills pores  interstices or interstitial regions within a structure  such as a polycrystalline structure. Thermally stable embodiments of PCD material may comprise at least a region from which catalyst material has been removed from the interstices  leaving interstitial voids between the diamond grains. As used herein  a “thermally stable PCD” structure is a PCD structure at least a part of which exhibits no substantial structural degradation or deterioration of hardness or abrasion resistance after exposure to a temperature above about 400 degrees centigrade.

With reference to FIG 1A and FIG 1B  an embodiment of a PCD composite compact element 100 may comprise a thermally stable PCD structure 120 bonded to the substrate 130 by means of a bond material in the form of a bond layer 140 between the PCD structure 120 and the substrate 130. In one version of the embodiment  the PCD structure 120 may be substantially free of material capable of functioning as solvent / catalyst for diamond. In another version of the embodiment  the PCD structure 120 may include non-metallic solvent / catalyst for diamond.

With reference to FIG 2  an embodiment of a PCD composite compact element 100 may comprise a first PCD structure 122 bonded to a second PCD structure 124 by means of a bond material in the form of a bond layer 140 between the first PCD structure 122 and the second PCD structure 124. The first PCD structure 122 may be more thermally stable than the second PCD structure 124. The second PCD structure 124 may be integrally bonded to a cemented carbide substrate 130.

With reference to FIG 3  an embodiment of a PCD composite compact element 100 may comprise a first PCD structure 122 bonded to a second PCD structure 124 by means of a bond material in the form of a bond layer 140 between the first PCD structure 122 and the second PCD structure 124. The second PCD structure 124 may be bonded by means of a bond material in the form of a bond layer 142 between the second PCD structure 124 and the substrate 140.

With reference to FIG 4  an embodiment of a PCD composite compact element 100 may comprise a first PCD structure 122 bonded to a second PCD structure 124 by means of a bond material in the form of a bond layer 140 between the first PCD structure 122 and the second PCD structure 124. The second PCD structure 124 may not be bonded or otherwise joined to a cemented carbide substrate.

With reference to FIG 5  an embodiment of a PCD composite compact element 100 may comprise a PCD structure 120 bonded to the substrate 130 by means of a bond material in the form of a bond layer 140  and the substrate 130 may include diamond particles 132 dispersed within it.

“Young’s modulus” is a type of elastic modulus and is a measure of the uniaxial strain in response to a uniaxial stress  within the range of stress for which the material behaves elastically. A preferred method of measuring the Young’s modulus E is by means of measuring the transverse and longitudinal components of the speed of sound through the material  according to the equation E = 2?.CT2(1 + ?)  where ? = (1 – 2 (CT / CL)2) / (2 – 2 (CT / CL)2)  CL and CT are respectively the measured longitudinal and transverse speeds of sound through it and ? is the density of the material. The longitudinal and transverse speeds of sound may be measured using ultrasonic waves  as is well known in the art. Where a material is a composite of different materials  the mean Young’s modulus may be estimated by means of one of three formulas  namely the harmonic  geometric and rule of mixtures formulas as follows: E = 1 / ( f1 / E1 + f2 / E2) ); E = E1 f1 + E1 f2; and E = f1 E1 + f2 E2; in which the different materials are divided into two portions with respective volume fractions of f1 and f2  which sum to one.

With reference to FIG 6  an embodiment of a PCD composite compact element 100 may comprise a PCD structure 120 bonded to a cemented carbide substrate 130 by means of a bond material in the form of a bond layer 140  in which the PCD structure 120 may comprise a first portion 122 integrally formed with a second portion 124 and the first and second portions may have different microstructure  composition or diamond particle size distribution  or combination of these  and different properties  such as strength or Young’s modulus.

In the embodiments described with reference to FIG 1A  FIG 1B  FIG 2  FIG 3  FIG 4  FIG 5 and FIG 6  the bond material may comprise or consist of a braze alloy material and the bond layer 140 may be a braze layer. In one embodiment  the bond material may comprise or consist of an epoxy material for bonding or joining ceramic materials.

With reference to FIG 7  an embodiment of an earth-boring rotary drill bit 200 of the present invention includes  for example  a plurality of cutting elements 100 as previously described herein with reference to FIG 1. The earth-boring rotary drill bit 200 includes a bit body 202 that is secured to a shank 204 having a threaded connection portion 206 (e.g.  a threaded connection portion 206 conforming to industry standards such as those promulgated by the American Petroleum Institute (API)) for attaching the drill bit 200 to a drill string (not shown). The bit body 202 may comprise a particle-matrix composite material or a metal alloy such as steel. The bit body 202  may be secured to the shank 204 by one or more of a threaded connection  a weld  and a braze alloy at the interface between them. In some embodiments  the bit body 202 may be secured to the shank 204 indirectly by way of a metal blank or extension between them  as known in the art.

The bit body 202 may include internal fluid passageways (not shown) that extend between the face 203 of the bit body 202 and a longitudinal bore (not shown)  which extends through the shank 204 the extension 208 and partially through the bit body 202. Nozzle inserts 224 also may be provided at the face 203 of the bit body 202 within the internal fluid passageways. The bit body 202 may further include a plurality of blades 216 that are separated by junk slots 218. In some embodiments  the bit body 202 may include gage wear plugs 222 and wear knots 228. A plurality of PDC cutting elements 100 of one or more of embodiments as previously described herein may be mounted on the face 203 of the bit body 202 in cutting element pockets 212 that are located along each of the blades 216. In other embodiments  PDC cutting elements 100 as previously described with reference to FIG 1  FIG 2  FIG  3  FIG 4  FIG 5  FIG 6 or any other embodiment of a PDC cutting element of the present invention  may be provided in the cutting element pockets 212.

The cutting elements 100 are positioned to cut a subterranean formation being drilled while the drill bit 200 is rotated under weight on bit (WOB) in a bore hole about centreline L200.

In the field of quantitative stereography  particularly as applied to cemented carbide material  “contiguity” is understood to be a quantitative measure of inter-phase contact. It is defined as the internal surface area of a phase shared with grains of the same phase in a substantially two-phase microstructure (Underwood  E.E  “Quantitative Stereography”  Addison-Wesley  Reading MA 1970; German  R.M. “The Contiguity of Liquid Phase Sintered Microstructures”  Metallurgical Transactions A  Vol. 16A  July 1985  pp. 1247-1252). As used herein  “diamond grain contiguity” ? is a measure of diamond-to-diamond contact or bonding  or a combination of contact and bonding within PCD material  and is calculated according to the following formula using data obtained from image analysis of a polished section of PCD material:

? = 100 * [2*(? -?)]/[(2*(? - ?))+?]  where ? is the diamond perimeter  and ? is the binder perimeter.

As used herein  the “diamond perimeter” is the fraction of diamond grain surface that is in contact with other diamond grains. It is measured for a given volume as the total diamond-to-diamond contact area divided by the total diamond grain surface area. The binder perimeter is the fraction of diamond grain surface that is not in contact with other diamond grains. In practice  measurement of contiguity is carried out by means of image analysis of a polished section surface. The combined lengths of lines passing through all points lying on all diamond-to-diamond interfaces within the analysed section are summed to determine the diamond perimeter  and analogously for the binder perimeter.

FIG 8 shows an example of a processed SEM image of a polished section of a PCD structure  showing the boundaries 360 between diamond grains 320. These boundary lines 360 were calculated by the image analysis software and were used to measure the diamond perimeter and subsequently for calculating the diamond grain contiguity. The non-diamond regions 340  which may be filled interstices or voids  for example  are indicated as dark areas. The binder perimeter was obtained from the cumulative length of the boundaries 360 between the diamond 320 and the non-diamond or interstitial regions 340.

FIG 9  FIG 10 and FIG 11 show non-limiting examples of multimodal grain size distributions of diamond grains within embodiments of PCD structures  for the purpose of illustration. As used herein  a “multimodal” size distribution of a mass of grains is understood to mean that the grains have a size distribution with more than one peak 400  each peak 400 corresponding to a respective “mode”. Multimodal polycrystalline bodies may be made by providing more than one source of a plurality of grains  each source comprising grains having a substantially different average size  and blending together the grains or grains from the sources. Measurement of the size distribution of the blended grains may reveal distinct peaks corresponding to distinct modes. When the grains are sintered together to form the polycrystalline body  their size distribution may be further altered as the grains are compacted against one another and fractured  resulting in the overall decrease in the sizes of the grains. Nevertheless  the multimodality of the grains may still be clearly evident from image analysis of the sintered article.

The size of grains is expressed in terms of equivalent circle diameter (ECD). As used herein  the “equivalent circle diameter” (ECD) of a particle is the diameter of a circle having the same area as a cross section through the particle. The ECD size distribution and mean size of a plurality of particles may be measured for individual  unbonded particles or for particles bonded together within a body  by means of image analysis of a cross-section through or a surface of the body. Unless otherwise stated herein  dimensions of size  distance  perimeter  ECD  mean free path and so forth relating to grains and interstices within PCD material  as well as the grain contiguity  refer to the dimensions as measured on a surface of  or a section through a body comprising PCD material and no stereographic correction has been applied. For example  the size distributions of the diamond grains as shown in FIG 9  FIG 10 and FIG 11 were measured by means of image analysis carried out on a polished surface  and a Saltykov correction was not applied.

In one embodiment of the invention  the PCD structure may comprise a first portion formed of a PCD material comprising diamond grains having at least three modes in the multimodal size distribution as shown in FIG 9  and a second portion formed of a PCD material comprising diamond grains having at least four-modes multimodal size distribution as shown in FIG 10  the mean size of the grains in the first portion being substantially less than that in the second portion  and the first and second portions of the PCD structure being integrally formed with each other. The PCD structure may be brazed to the substrate with the second portion of the PCD structure proximate the substrate and the first portion of the PCD structure remote from the substrate.

In one embodiment of the invention  the PCD structure may comprise a first portion formed a PCD material comprising diamond grains having two modes in the multimodal size distribution as shown in FIG 11  and a second portion formed of a PCD material comprising diamond grains having at least three modes in the multimodal size distribution as shown in FIG 9  the first and second portions of the PCD structure being integrally formed with each other. The PCD structure may be brazed to the substrate with the second portion of the PCD structure proximate the substrate and the first portion of the PCD structure remote from the substrate.

In some embodiments  the PCD structure may be as taught in PCT publication number WO2009/027948  which discloses a PCD structure comprising a diamond phase and a filler material  the filler material comprising a ternary carbide of the general formula: Mx M""y Cz wherein; M is at least one metal selected from the group consisting of the transition metals and the rare earth metals; M"" is a metal selected from the group consisting of the main group metals or metalloid elements and the transition metals Zn and Cd; x is from 2.5 to 5.0; y is from 0.5 to 3.0; and z is from 0.1 micron to 1. 2 microns.

In some embodiments  the PCD structure may be as taught in PCT publication number WO2009/027949  which discloses PCD composite material comprising inter-grown diamond grains and a filler material  the filler material comprising a tin-based inter-metallic or ternary carbide compound formed with a metallic solvent / catalyst. The use of CoSn may facilitate PCD sintering at high-pressure high temperature conditions at which the temperature is between about 1 300 and about 1 450 degrees centigrade and the pressure is between about 5.0 and about 5.8 GPa. In some embodiments  substantially all of the cobalt may be removed from the PCD structure prior to brazing the structure to a substrate.

The homogeneity of the microstructure may be characterised in terms of the combination of the mean thickness of the interstices between the diamonds  and the standard deviation of this thickness. The homogeneity or uniformity of a PCD structure may be quantified by conducting a statistical evaluation using a large number of micrographs of polished sections. The distribution of a filler phase or of pores within the PCD structure may be easily distinguishable from that of the diamond phase using electron microscopy and can be measured in a method similar to that disclosed in EP 0 974 566 (see also WO2007/110770). This method allows a statistical evaluation of the average thicknesses or interstices along several arbitrarily drawn lines through the microstructure. The mean binder or interstitial thickness is also referred to as the "mean free path". For two materials of similar overall composition or binder content and average diamond grain size  the material that has the smaller average thickness will tend to be more homogenous  as this indicates a finer scale distribution of the binder in the diamond phase. In addition  the smaller the standard deviation of this measurement  the more homogenous is the structure. A large standard deviation indicates that the binder thickness varies widely over the microstructure and that the structure is not uniform.

As used herein  the “interstitial mean free path” within a polycrystalline material comprising an internal structure including interstices or interstitial regions  such as PCD  is understood to mean the average distance across each interstitial between different points at the interstitial periphery. The average mean free path is determined by averaging the lengths of many lines drawn on a micrograph of a polished sample cross section. The mean free path standard deviation is the standard deviation of these values. The diamond mean free path is defined and measured analogously.

In measuring the mean value and deviation of a quantity such as grain contiguity  or other statistical parameter measured by means of image analysis  several images of different parts of a surface or section are used to enhance the reliability and accuracy of the statistics. The number of images used to measure a given quantity or parameter may be at least about 9 or even up to about 36. The number of images used may be about 16. The resolution of the images needs to be sufficiently high for the inter-grain and inter-phase boundaries to be clearly made out. In the statistical analysis  typically 16 images are taken of different areas on a surface of a body comprising the PCD material  and statistical analyses are carried out on each image as well as across the images. Each image should contain at least about 30 diamond grains  although more grains may permit more reliable and accurate statistical image analysis.

In some embodiments  the PCD structure may be as taught in PCT publication number WO2007/020518  which discloses polycrystalline diamond a polycrystalline diamond abrasive element comprising a fine grained polycrystalline diamond material characterised in that it has an interstitial mean-free-path value of less than 0.60 microns  and a standard deviation for the interstitial mean-free-path that is less than 0.90 microns. In one embodiment  the polycrystalline diamond material may have a mean diamond grain size of from about 0.1 to about 10.5.

In some embodiments  the PCD structure may be manufactured using a method including sintering of diamond grains in an ultra-high pressure and temperature (HPHT) process in the presence of a solvent / catalyst material for diamond and then removing solvent / catalyst material from interstices within the PCD structure. Catalyst material may be removed from the PCD table using methods known in the art such as electrolytic etching  acid leaching and evaporation techniques. In some embodiments  a masking or passivating medium may be introduced into pores within the PCD structure.

Solvent / catalyst material may be introduced to an aggregated mass of diamond grains for sintering in various ways known in the art. One way includes depositing metal oxide onto the surfaces of a plurality of diamond grains by means of precipitation from an aqueous solution prior to forming their consolidation into an aggregated mass. Such methods are disclosed in PCT publications numbers WO2006/032984 and also WO2007/110770. Another way includes preparing or providing metal alloy including a catalyst material for diamond  such as cobalt-tin alloy  in powder form and blending the powder with the plurality of diamond grains prior to their consolidation into an aggregated mass. The blending may be carried out by means of a ball mill. Other additives may be blended into the aggregated mass.

In one embodiment  the aggregated mass of diamond grains  including any solvent / catalyst material particles or additive material particles that may have been introduced  may be formed into an unbonded or loosely bonded structure  which may be placed onto a cemented carbide substrate. The cemented carbide substrate may contain a source of catalyst material for diamond  such as cobalt. The assembly of aggregated mass and substrate may be encapsulated in a capsule suitable for an ultra-high pressure furnace apparatus and subjecting the capsule to a pressure of greater than 6 GPa. Various kinds of ultra-high pressure apparatus are known and can be used  including belt  torroidal  cubic and tetragonal multi-anvil systems. The temperature of the capsule should be high enough for the source of catalyst material to melt and low enough to avoid substantial conversion of diamond to graphite. The time should be long enough for sintering to be completed but as short as possible to maximise productivity and reduce costs.

As noted previously  the PCD structure may have an oxidation onset temperature of at least about 800 degrees centigrade. Embodiments of such PCD may have superior thermal stability and exhibit superior performance in applications such as oil and gas drilling  wherein the temperature of a PCD cutter element can reach several hundred degrees centigrade. Oxidation onset temperature is measured by means of thermo-gravimetric analysis (TGA) in the presence of oxygen  as is known in the art.

In some embodiments of the invention  the bond material may comprise a high shear strength epoxy resin or epoxy paste material for joining ceramic materials  for example epoxy paste under the trade name ES550™ from Permabond™  or solder material. In one embodiment  the bond material may comprise or consist of an organic adhesive.

In some embodiments the PCD structure may be brazed to the substrate by means of microwave brazing  wherein the braze material is heated by means of microwave energy. Brazing the PCD using an active braze material in a very high vacuum may result in braze strength high enough for the PCD compact element to be technically and economically viable. Active brazing is discussed by H.R. Prabhakara (in “Vacuum brazing of ceramics and graphite to metals”  Bangalore Plasmatek Pvt.Ltd  129  Block –14  Jeevanmitra Colony I-Phase  Bangalore 560 078).

In some embodiments  the braze alloy may have a melting onset temperature  at which the alloy begins to melt  of at most about 1 050 degrees centigrade  at most about 1 000 degrees centigrade or at most about 950 degrees centigrade  or even at most about 900 degrees centigrade. Such embodiments may have the advantage of permitting a PCD structure to be brazed to a substrate at a temperature sufficiently low that thermally-induced degradation the PCD may be reduced or avoided. The process of brazing PCD to a substrate may be carried out in a substantially inert atmosphere that inhibits oxidation  which may have the advantage of resulting in a stronger braze bond.

In one embodiment  the braze alloy may comprise an element that readily reacts with carbon to form carbide  and in one embodiment  the braze alloy may be a reactive braze alloy  which may effectively wet the surface of diamond.

In one embodiment  the braze alloy may contain Ti  which may effectively wet the surface of the diamond. In some embodiments  the braze alloy may contain Cu  Ni  Ag or Au  which may effectively wet a cemented carbide substrate. One type of reactive braze alloy may modify the surface of the diamond operative to make it more readily wettable. Examples of this type of reactive braze alloys may comprise Mo  W  Ti  Ta  V and Zr. In some embodiments  the braze alloy may comprise or consist essentially of Ti  Cu and Ag  also referred to as “TiCuSil” braze alloys  which may comprise a eutectic composition of Ag and Cu  as well as an amount of Ti. For example  the weight ratio of Ti to Cu to Ag may be 4.5 : 26.7 : 68.8  or the ratio of Ti to Cu to Ag may be 10.0 : 25.4 : 64.6  or the ratio of Ti to Cu to Ag may be 15.0 : 24.0 : 61.0. In one embodiment  the braze alloy may comprise about 63.00% Ag  about 32.25% Cu and about 1.75% Ti  and may be available under the trade name of Cusil™ ABA. In one embodiment  the braze alloy may comprise about 70.5% Ag  about 26.5% Cu and about 3.0% Ti  available under the trade name of CB4 

Braze alloys having a high strength may include Cu  alloys comprising Ni and Cr alloys  and brazes containing high percentages of elements such as Pd and similar high strength materials  and Cr-based active brazes. In one embodiment  the braze alloy may comprise or consist essentially of Ni  Pd and Cr. In some embodiments  the ratio of the weight ratio of Pd to Ni may be in the range from about 0.4 to about 0.8. In one embodiment  the braze alloy may comprise Ni  Pd  Cr  B and Si  and in one embodiment  the weight ratio of Ni to Pd to Cr to B to Si may be about 50 : 36 : 10.5 : 3 : 0.5  or the weight ratio of Ni to Pd to Cr to B to Si may be about 57 : 30 : 10.5 : 2.4. Braze alloy material comprising Ni  Pd  Cr  B may be obtained under the trade name Palnicro™ 36M from WESGO Metals™. In one embodiment  the braze alloy may comprise Ag  Cu  Ni  Pd and Mn  and in one embodiment  the weight ratio of Ag to Cu to Ni to Pa and Mn may be about 25 : 37 : 10 : 15 and 13. Such a braze alloy may be available under the trade name PALNICUROM™ 10. In one embodiment  the braze alloy may comprise about 64% iron and about 36% nickel  which may be referred to as Invar. In one embodiment  the braze material may comprise a substantially unalloyed metal such as Co. In some embodiments  the braze alloy may comprise at least one element selected from the group consisting of Cr  Fe  Si  C  B  P  Mo  Ni  Co  W  and Pd. One example of a suitable braze alloy may be available from Metglas™ under the trade name MBF 15.

In some embodiments  the braze alloy may comprise at least one of Cu  Ag or Au  and in some embodiments  the braze alloy may further comprise at least one of Ti  V  Cr  Mn  Zr  Nb  Mo  Hf  Ta  W or Re. For example  the braze alloy may contain Au and Ta  or the braze alloy may contain Ag  Cu and Ti. In some embodiments  the braze material may comprise at least one of Fe  Co  Ni or Mn.

In one embodiment of the invention  the method may include coating a surface of the PCD structure to prepare it form brazing  and then brazing the PCD structure to the substrate. Examples of coatings for this purpose and methods of applying them are described in United States patents numbers 5 500 248; 5 647 878l; 5 529 805 and PCT patent application publication number 2008/142657.

In one embodiment  the braze layer may contain dispersed ceramic particles  and in one embodiment  the ceramic particles may comprise a carbide material  such as silicon carbide  or a super-hard material such as diamond. In some embodiments  the ceramic particles may have mean size of less than about 20 microns or less than about 10 microns. In some embodiments of the invention  the presence of the ceramic particles in the braze layer may to strengthen it and may reduce the likelihood of the composite compact element failing as a result of the braze.

Embodiments of the invention may be used as gauge trimmers on other types of earth-boring tools  such as cones of roller cone drill bits  reamers  mills  bi-centre bits  eccentric bits  coring bits and so-called hybrid bits that include both fixed cutters and rolling cutters.

Grain contiguity may be determined from SEM images by means of image analysis software. In particular  software having the trade name analySIS Pro from Soft Imaging System® GmbH (a trademark of Olympus Soft Imaging Solutions GmbH) may be used. This software has a “Separate Grains” filter  which according to the operating manual only provides satisfactory results if the structures to be separated are closed structures. Therefore  it is important to fill up any holes before applying this filter. The “Morph. Close” command  for example  may be used or help may be obtained from the “Fillhole” module. In addition to this filter  the “Separator” is another powerful filter available for grain separation. This separator can also be applied to colour- and grey-value images  according to the operating manual.

As used herein  “transverse rupture strength” (TRS) is measured by subjecting a specimen in the form of a disc to a load applied at three points  two applied on one side of the specimen and one applied on the opposite side  and increasing the load at a loading rate until the specimen fractures. Such a measurement may also be referred to as a three-point bending test  and has been described by Borger et al. (Borger  A.  P. Supansic and R. Danzer  “The ball on three balls test for strength testing of brittle discs: stress distribution in the disc”  Journal of the European Ceramic Society  2002  volume 22  pp. 1425-1436). With reference to FIG 12  a specimen 510 of the material to be tested is placed between a load ball 520 and two support balls 530  and supported by a guide body 570. The load ball 520 is supported by a stamp 560  which is supported laterally and guided by a guide body 570  and a chock 580 is disposed between respective parts of the guide body 570 and the stamp 560 and establishes a proximity limit to the movement of the stamp 560 with respect to the guide body 570. A punch 550 abuts support balls 530  which are disposed between the punch 550 and the specimen 510. An axial load 540 is applied to the punch 550 causing the load ball 520 and the support balls 530 to be urged against the specimen 510 from opposite sides. The load is increased at a certain loading rate from a lower limit until evidence of fracture is observed in the specimen 510. As a non-limiting example  an Instron™ 5500R universal testing machine having a load cell of 10KN may be used for measuring transverse rupture strength as described above. The loading rate may be about 0.9 mm/min. The transverse rupture strength ? in MPa is calculated as f(F).F/t2  where F is the measured load  in Newtons  at which the specimen begins to fracture  t is the thickness of the specimen and f(F) is a dimensionless constant dependent on the load and the material being tested. In the case of PCD  f(F) = 1.620211 – 0.0082 X (F – 3000) / 1000.

The specimen in the form of a round disc for use in the TRS measurement described above is prepared as follows. A PCD construction comprising a PCD structure joined to a substrate is provided  the outer diameter of which is ground to 16 mm or 19 mm. The substrate is removed  leaving a free-standing the PCD disc  which is then lapped to a thickness in the range from about 1.30 mm to about 2.00 mm. The PCD disc may be treated in acid to remove some or substantially all of the material in the interstices between the diamond grains.

The K1C toughness of a PCD disc is measured by means of a diametral compression test  which is described by Lammer ("Mechanical properties of polycrystalline diamonds"  Materials Science and Technology  volume 4  1988  p. 23.) and Miess (Miess  D. and Rai  G.  "Fracture toughness and thermal resistances of polycrystalline diamond compacts"  Materials Science and Engineering  1996  volume A209  number 1 to 2  pp. 270-276).

Known PCD composite compact elements comprising PCD structures brazed to substrates have lacked commercially success  particularly in harsh applications such as drilling into rock  especially in the oil and gas drilling industry. Such applications require cutter compact elements capable of maintaining extreme abrasion resistance and high strength at high temperatures experienced in use  typically in excess of 600 degrees centigrade. While wanting not to be bound by theory  brazing of PCD to carbide may give rise to high internal stresses within the compact element proximate the braze interface  resulting in cracking of the PCD and / or the substrate or the delamination of the PCD even before the compact element is used to bore into rock. Embodiments of PCD composite compact elements according to the invention  particularly embodiments in which the PCD structure is thermally stable may be economically viable and commercially successful.

Embodiments of the invention in which the PCD structure has a mean Young’s modulus of at least about 800 GPa may better retain its mechanical integrity and robustness after being bonded to the substrate. If the Young’s modulus is substantially less than about 800 GPa  or if the transverse rupture strength is substantially less than about 900 MPa  the PCD structure may not be able to cut rock efficiently and may wear too rapidly. Embodiments of PCD that have a homogeneous microstructure  characterised in terms of the combination of the interstitial mean free path and the standard deviation of the interstitial mean free path  may have enhanced resistance to mechanical and thermal stress and shock  as may be experience when brazing the PCD to a substrate and using the composite compact to degrade or bore into rock.

Embodiments having the combination of the high contiguity and / or high homogeneity and / or reduced content of metallic solvent / catalyst within the PCD structure  and a size distribution comprising at least two or three peaks or modes  have the advantage of bonding particularly well using conventional brazing. Embodiments may exhibit superior durability over prior art cutter elements comprising PCD brazed to a substrate.

Embodiments of the invention have the advantage that the strength with which the PCD structure is bonded to the substrate may be substantially enhanced. In particular  embodiments in which the PCD structure is brazed to the substrate and in which the PCD structure contains braze material to a depth of at least about 2 microns from an interface with the braze layer may have exhibit a particularly enhanced strength of bonding. Consequently  the mechanical properties and working life of such embodiments may be enhanced  particularly when used to bore into rock.

Embodiments of the invention in which the shear strength of the bond between the PCD structure and the substrate is at least about 100 MPa and at most about 500 MPa  may have the advantage that conventional brazing methods may be adequate.

Embodiments of the invention in which the PCD structure is thermally stable have the advantage that the PCD structure better retains its structural integrity and key mechanical properties after being bonded to the substrate by means of a method involving heating the PCD structure  such as brazing. Embodiments of the invention in which the PCD structure has a filler comprising carbide or inter-metallic compounds may have enhanced thermal stability and better retain key mechanical properties after being bonded to the substrate  such as by brazing.

Embodiments of the invention in which the substrate comprises cemented carbide and includes diamond particles dispersed in it may have enhanced mechanical robustness  particularly fracture resistance.

Embodiments of the invention in which the PCD structure comprises at least 90 volume percent diamond grains having a mean size of at most about 10 microns may be especially advantageous. Embodiments of PCD structures having a multi-modal diamond grain size distribution have sufficient strength to retain better their mechanical integrity and key properties after bonding to the substrate  such as by brazing.

Embodiments of the invention may have the advantage that the composition of the PCD structure  particularly the composition of the filler material  may be selected with fewer constraints associated with the composition of the substrate. PCD structures having desirable properties  particularly high thermal stability  can be made separately from the substrate and then bonded to the substrate using known brazing materials and methods  thereby improving the performance of the PCD tool without incurring substantial additional costs.

Embodiments of the invention are described in more detail with reference to the examples below  which are not intended to limit the invention.

Example 1

A PCD disc having thickness of about 2.2 millimetres and diameter of about 16 mm was provided using a known high-pressure high temperature method. The substrate to which the PCD was bonded during the sintering step was removed by grinding  leaving an un-backed  free-standing PCD disc. The PCD comprised coherently bonded diamond grains having a multi-modal size distribution with mean equivalent circle diameter of about 9 microns. Microstructural data for the PCD is shown in Table 1  in which the mean grain size is expressed in terms of equivalent circle diameter and the values shown in parentheses are the respective standard deviations.

Mean diamond grain size 
microns Diamond content of PCD  volume % Filler mean free path  microns Diamond grain contiguity  %

9.0 (4.0)
91 (0.4) 0.6 (0.5) 62.0(1.7)

Table 1

The PCD disc was then treated (leached) in acid to remove substantially all of the cobalt solvent / catalyst material throughout the entire PCD structure.

Several additional discs  each having a diameter of about 19 mm  were made as described above and subjected to a range of tests to measure mechanical properties. Mechanical properties of the PCD discs after acid treatment are shown in Table 2  in which the values shown in parentheses are the respective standard deviations. It was found that the TRS of the PCD disc decreased from about 1 493 MPa before leaching to about 1 070 MPa after leaching (i.e. by approximately 28%)  and the Young’s modulus decreased from about 1 025 GPa to about 864 GPa (i.e. by about 15% to 16%).

Transverse rupture strength  MPa K1C toughness  MPa.m1/2 Young’s modulus  GPa

1 070 (100)

6.8 (0.2)
864 (14)

Table 2

A cobalt-cemented tungsten carbide substrate having substantially the same diameter as the 16 mm PCD disc was provided. A foil of active braze material having thickness of about 100 microns was sandwiched between the PCD disc and the substrate to form a pre-compact element assembly. The braze material comprised 63.00% Ag  32.25% Cu and 1.75% Ti  and is available under the trade name of Cusil™ ABA. Prior to brazing  the PCD disc was ultrasonically cleaned  and both the tungsten carbide substrate and the braze foil was slightly ground and then ultrasonically cleaned.

The pre-compact element assembly was subjected to heat treatment in a vacuum. The temperature was increased to 920 degrees centigrade over 15 minutes  held at this level for 5 minutes and then reduced to ambient temperature over about 8 to 9 hours. A vacuum of at least 10-5 millibar was maintained during the heat treatment. Care was taken to avoid or minimise the amount of oxygen and other impurities in the furnace environment. Furthermore  a furnace with convection heating and low temperature gradients was used because the components to be brazed and the braze material should all reach the desired temperature in relatively short time.

The molten braze material was found to infiltrate into the PCD disc to a depth in the range from 10 to 20 microns  leaving a braze layer of about 50 microns to about 80 microns between the PCD and WC substrate. The shear strength of the braze bond was measured to be in the range from 110 MPa to 150 MPa.

A control PCD composite compact element that had not been detached from its original substrate and had not been treated in acid was provided for comparison. The brazed and control composite compacts were processed to form respective cutter elements and subjected to a wear test involving using them to machine a granite block mounted on a vertical turret milling apparatus. The test result is expressed in terms of the depth of the wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth  the better. After 55 passes  the wear scar depth of the compact element was about 3.5 mm  compared to about 4 mm for the control element.

Example 2

A PCD compact element having a diameter of 16 mm was prepared as described in Example 1  except that a different braze material was used. The braze material comprised 70.5% Ag  26.5% Cu and 3.0% Ti  available under the trade name of CB4  and the brazing step was carried out at a temperature of 950 degrees centigrade. The molten braze material was found to infiltrate into the PCD disc to a depth in the range from 5 to 10 microns. The shear strength of the braze bond was found to be in the range from 110 MPa to 150 MPa.

The brazed compact element was subjected to a wear test as described in Example 1. After 55 passes  the wear scar depth of the compact element was about 2 mm.

Example 3

Example 1 was repeated  except that the PCD disc comprised coherently bonded diamond grains having a multi-modal size distribution with mean equivalent circle diameter of about 4.6 micrometres. Microstructural data for the PCD is shown in table 3.

Mean diamond grain size 
microns Diamond content of PCD  volume % Filler mean free path  microns Diamond grain contiguity  %

4.6 (1.3)
90.2 (0.3) 0.4 (0.3) 58.7 (1.7)

Table 3

The PCD disc was then treated in acid to remove substantially all of the cobalt solvent / catalyst material within the interstices between the diamond grains  as is well known in the art.

Several additional discs  each having a diameter of about 19 mm  were made as described above and subjected to a range of tests to measure mechanical properties. Key mechanical properties of the PCD after acid treatment are shown in table 4.

Transverse rupture strength  MPa K1C toughness  MPa.m1/2 Young’s modulus  GPa
1 200 (120)
7.8 (0.8)
Not measured

Table 4

The molten braze material was found to infiltrate into the PCD disc to a depth in the range from about 10 microns to 20 about microns. The shear strength of the braze bond was measured to be in the range from 110 MPa to 150 MPa.

The brazed PCD compact element was subjected to a further wear test  wherein the compact element was used to mill a block of granite. After a cutting length of at least 6 000 millimetres  no failure due to the braze joint was observed.

Example 4

PCD composite compact elements each comprising a layer of PCD material having a diameter of 16 mm  in which the mean diamond grain size was about 9 microns and the content of cobalt was about 9.0 volume % were provided by sintering the diamond grains onto respective cemented carbide substrates at a pressure of about 5.5 GPa and a temperature of about 1400 degrees centigrade. Microstructural data for the PCD is shown in Table 5  in which the mean grain size is expressed in terms of equivalent circle diameter.

Mean diamond grain size 
microns Diamond content of PCD  volume % Filler mean free path  microns Diamond grain contiguity  %

9.0 (4.0)
91 (0.4) 0.6 (0.5) 62.0(1.7)

Table 5

The substrates were removed from the PCD layers  which were then treated in acid to remove substantially all of the cobalt filler material. Inductively coupled plasma (ICP) analysis confirmed the residual presence of about 2 weight %  which is about 1.1 volume % Co in the PCD structure. The residual cobalt may have been trapped within substantially closed pores of the PCD structure. Key mechanical properties of the PCD discs after acid treatment are shown in Table 6  in which the values shown in parentheses are the respective standard deviations. The oxidation onset temperature of the PCD in this cutter was measured to be 870 degrees centigrade.

Transverse rupture strength  MPa K1C toughness  MPa.m1/2 Young’s modulus  GPa

831

5.6 (0.3)
844

Table 6

A treated PCD structure was brazed onto a cemented tungsten carbide substrate using an alloy comprising 70.5 weight % Ag  26.5 weight % Cu and 3.0 weight % Ti  a formulation available under the trade name CB4 from BrazeTec™. The brazing was carried out in a vacuum furnace  under a vacuum of 10-6 mbar  at 950 degrees centigrade for about 5 minutes. The shear strength of the braze bond between the PCD structure and the substrate was about 287 MPa at room temperature and about 224 MPa at 300 degrees centigrade.

A control PCD composite compact element that had not been detached from its original substrate and had not been treated in acid was provided for comparison. The brazed compact and the control composite compacts were processed to form respective cutter elements and subjected to a wear test involving using them to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 5.2 mm2  compared to about 18.9 mm2 for the control element.

Example 5

PCD structures in the form of discs having a diameter of 16 mm and in which the diamond grains had a mean size of about 9 microns were manufactured by sintering the grains onto respective substrates at a pressure of about 6.8 GPa and a temperature of about 1 400 degrees centigrade. Microstructural data for the PCD is shown in Table 7  in which the mean grain size is expressed in terms of equivalent circle diameter.

Mean diamond grain size 
microns Diamond content of PCD  volume % Filler mean free path  microns Diamond grain contiguity  %

9 (4)
91.4 (0.4) 0.7 (0.6) 63.0 (1.5)

Table 7

The substrates were removed and the PCD structures were treated in acid to remove substantially all of the cobalt filler material. Key mechanical properties of the PCD discs after acid treatment are shown in Table 8  in which the values shown in parentheses are the respective standard deviations.

Transverse rupture strength  MPa K1C toughness  MPa.m1/2 Young’s modulus  GPa

983
Not measured 927

Table 8

A treated PCD disc was brazed onto a cemented tungsten carbide substrate using an alloy comprising 70.5 weight % Ag  26.5 weight % Cu and 3.0 weight % Ti  a formulation available under the trade name CB4 from BrazeTec™  as described in Example 4.

The brazed compact was processed to form a cutter element and subjected to a wear test involving using it to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 3.26 mm2  compared to about 18.9 mm2 for the control element described in Example 4.

Example 6

PCD structures in the form of discs having a diameter of 16 mm and in which the diamond grains had a mean size of about 4 microns and which contained about 10 volume % cobalt  were manufactured by sintering the grains onto respective substrates at a pressure of about 5.5 GPa and a temperature of about 1 400 degrees centigrade. Microstructural data for the PCD is shown in Table 9  in which the mean grain size is expressed in terms of equivalent circle diameter.

Mean diamond grain size 
microns Diamond content of PCD  volume % Filler mean free path  microns Diamond grain contiguity  %

4.2 (1.6)
89.2 (0.5) 0.4 (0.3) 65 (1)

Table 9

The substrate was removed and the PCD structure was treated in acid to remove substantially all of the cobalt filler material. Key mechanical properties of the PCD disc after acid treatment are shown in Table 8  in which the values shown in parentheses are the respective standard deviations.

Transverse rupture strength  MPa K1C toughness  MPa.m1/2 Young’s modulus  GPa

1 058
6.9 846

Table 10

The treated PCD disc was brazed onto a cemented tungsten carbide substrate using an alloy comprising 70.5 weight % Ag  26.5 weight % Cu and 3.0 weight % Ti  a formulation available under the trade name CB4 from BrazeTec™  as described in Example 4.

A control PCD composite compact element that had not been detached from its original substrate and had not been treated in acid was provided for comparison. The brazed and control composite compacts were processed to form respective cutter elements and subjected to a wear test involving using them to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 3.33 mm2  compared to about 4.09 mm2 for the control element.

Example 7

PCD structures in the form of discs  in which the diamond grains had a mean size of about 4 microns and containing about 10 volume % cobalt  were manufactured by sintering the grains onto respective substrates at a pressure of about 6.8 GPa and a temperature of about 1 400 degrees centigrade. Microstructural data for the PCD is shown in Table 11  in which the mean grain size is expressed in terms of equivalent circle diameter.

Mean diamond grain size 
microns Diamond content of PCD  volume percent Filler mean free path  microns Diamond grain contiguity  percent

4.3 (1.2)
89 (1) 1 (1.6) 57.8 (1)

Table 11

The substrates were removed and the PCD structures were treated in acid to remove substantially all of the cobalt filler material.

A treated PCD was brazed onto a cemented tungsten carbide substrate using an alloy comprising 70.5 weight % Ag  26.5 weight % Cu and 3.0 weight % Ti  a formulation available under the trade name CB4 from BrazeTec™  as described in Example 4.

The brazed composite compact was processed to form a utter element and subjected to a wear test involving using it to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 3.28 mm2  compared to about 4.09 mm2 for the control element described in Example 6.

Example 8

PCD discs were provided and treated as described in Example 4  and a treated PCD disc was brazed onto a cemented tungsten carbide substrate using a braze alloy comprising 86.0 weight % Cu  12.0 weight % Mn and 2.0 weight % Ni at 1050 degrees centigrade for about 5 minutes in vacuum. The braze material was available as 21/80 from BrazeTec™.

The brazed composite compact was processed to form a cutter element and subjected to a wear test involving using it to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 3.65 mm2  compared to about 18.9 mm2 for the control element described in Example 4.

Example 9

PCD discs were provided and treated as described in Example 4  and a treated disc was glued onto a cemented tungsten carbide substrate using Permabond ES550™ epoxy resin at about 100 degrees centigrade for about 2 hours.

The brazed and control composite compact was processed to form a cutter element and subjected to a wear test involving using it to machine a granite block mounted on a vertical turret milling apparatus. The test result can be expressed in terms of the depth of the wear scar or area of wear scar at the cutting edge of the compact element after a given number of passes. The smaller the wear scar depth or area  the better. After 55 passes  the wear scar area of the example compact element was about 4.44 mm2  compared to about 18.9 mm2 for the control element described in Example 4.

Example 10

A PCD disc was provided and treated as described in Example 4  and was brazed onto a cemented tungsten carbide substrate using a braze alloy comprising 68.8 weight % Ag  26.7 weight % Cu and 4.5 weight % Ti alloy at about 950 centigrade for about 5 minutes in vacuum. The braze material was available under the product name Ticusil™ from Wesgo™.

Example 11

A PCD disc was provided and treated as described in Example 4  and was brazed onto a cemented tungsten carbide substrate using a braze alloy comprising 68.8 weight % Ag  26.7 weight % Cu and 4.5 weight % Ti alloy at about 950 centigrade for about 5 minutes in an argon atmosphere. The braze material was available under the product name Ticusil™ from Wesgo™. The shear strength of the braze bond was about resultant cutting element had bond shear strength of 215 MPa at room temperature.

Claims

1. A PCD composite compact element comprising a substrate  a PCD structure bonded to the substrate  and a bond material bonding the PCD structure to the substrate; the PCD structure being thermally stable and having a mean Young’s modulus of at least 800 GPa  the PCD structure having an interstitial mean free path of at least 0.05 microns and at most 1.5 microns; the standard deviation of the mean free path being at least 0.05 microns and at most 1.5 microns.

2. A PCD composite compact element as claimed in claim 1  in which the bond material is a braze alloy in the form of a braze layer between the PCD structure and the substrate.

3. A PCD composite compact element as claimed in claim 2  in which the braze alloy has a melting onset temperature of at most 1 050 degrees centigrade and contains at least one element selected from the group consisting of Ti  V  Cr  Mn  Zr  Nb  Mo  Hf  Ta  W and Re.

4. A PCD composite compact element as claimed in claim 1  in which the bond material comprises an epoxy material for joining ceramic materials.

5. A PCD composite compact element as claimed in any one of the preceding claims  in which the substrate comprises PCD material.

6. A PCD composite compact element as claimed in any one of the preceding claims  in which the PCD structure has a mean diamond grain contiguity of at least 60 percent.

7. A PCD composite compact element as claimed in any one of the preceding claims  in which the PCD structure has transverse rupture strength of at least 900 MPa.

8. A PCD composite compact element as claimed in any one of the preceding claims  in which the PCD structure is not entirely porous and has a mean Young’s modulus of at least about 900 GPa  and a transverse rupture strength of least 1 000 MPa.

9. A PCD composite compact element as claimed in any one of the preceding claims  the PCD structure being thermally stable and containing braze material.

10. A PCD composite compact element as claimed in any one of the preceding claims  in which there is less than about 5 volume percent of solvent / catalyst for diamond in the PCD structure.

11. A PCD composite compact element as claimed in any one of the preceding claims  in which the PCD structure is at least partially porous.

12. A PCD composite compact element as claimed in any one of the preceding claims  in which the substrate includes diamond particles dispersed within it.

13. A PCD composite compact element as claimed in any one of the preceding claims  secured to a drill bit or other earth boring tool.

14. A method of making a PCD composite compact element as claimed in any one of the preceding claims  the method including providing a PCD structure  treating the PCD structure to remove filler material from between diamond grains and create pores  crevices or irregularities at a boundary of the PCD structure; and bonding the PCD structure to a substrate at the boundary by means of a bond material.

Abstract

A polycrystalline diamond (PCD) composite compact element 100 comprising a substrate 130  a PCD structure 120 bonded to the substrate 130  and a bond material in the form of a bond layer 140 bonding the PCD structure 120 to the substrate 130; the PCD structure 120 being thermally stable and having a mean Young’s modulus of at least about 800 GPa  the PCD structure 120 having an interstitial mean free path of at least about 0.05 microns and at most about 1.5 microns; the standard deviation of the mean free path being at least about 0.05 microns and at most about 1.5 microns. Embodiments of the PCD composite compact element may be for a tool for cutting  milling  grinding  drilling  earth boring  rock drilling or other abrasive applications  such as the cutting and machining of metal.