US20140311045A1 - Methods of forming a superhard structure or body comprising a body of polycrystalline diamond containing material - Google Patents

Methods of forming a superhard structure or body comprising a body of polycrystalline diamond containing material Download PDF

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US20140311045A1
US20140311045A1 US14/367,165 US201214367165A US2014311045A1 US 20140311045 A1 US20140311045 A1 US 20140311045A1 US 201214367165 A US201214367165 A US 201214367165A US 2014311045 A1 US2014311045 A1 US 2014311045A1
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diamond
metal
pcd
particles
precursor compound
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Geoffrey John Davies
Moosa Mahomed Adia
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Element Six Abrasives SA
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Element Six Abrasives SA
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
    • B24D18/00—Manufacture of grinding tools or other grinding devices, e.g. wheels, not otherwise provided for
    • B24D18/0009—Manufacture of grinding tools or other grinding devices, e.g. wheels, not otherwise provided for using moulds or presses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
    • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
    • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
    • B24D3/04—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic
    • B24D3/06—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic metallic or mixture of metals with ceramic materials, e.g. hard metals, "cermets", cements
    • B24D3/10—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic metallic or mixture of metals with ceramic materials, e.g. hard metals, "cermets", cements for porous or cellular structure, e.g. for use with diamonds as abrasives
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/25—Diamond
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
    • C04B35/528—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1026—Alloys containing non-metals starting from a solution or a suspension of (a) compound(s) of at least one of the alloy constituents
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
    • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
    • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds

Definitions

  • This disclosure relates to methods of making a superhard structure or body comprising a body of polycrystalline diamond containing material and a body made by such methods.
  • Polycrystalline diamond materials as considered in this disclosure consist of an intergrown network of diamond grains with an interpenetrating metallic network. This is illustrated schematically in FIG. 1 which shows the microstructure of PCD material comprising the intergrown network of diamond grains 1 with an inter-penetrating metallic network 2 with facets occurring at the diamond-metal interfaces 3 . Each grain has a degree of plastic deformation 4 . Newly crystallized diamond bonds 5 bond the diamond grains as shown in the inset of this figure.
  • the network of diamond grains is formed by sintering of diamond powders facilitated by molten metal catalyst/solvent for carbon at elevated pressures and temperatures.
  • the diamond powders may have a monomodal size distribution whereby there is a single maximum in the particle number or mass size distribution, which leads to a monomodal grain size distribution in the diamond network.
  • the diamond powders may have a multimodal size distribution where there are two or more maxima in the particle number or mass size distribution, which leads to a multimodal grain size distribution in the diamond network.
  • Typical pressures used in this process are in the range of around 4 to 7 GPa but higher pressures up to 10 GPa or more are also practically accessible and can be used.
  • the temperatures employed are above the melting point at such pressures of the metals.
  • the metallic network is the result of the molten metal freezing on return to normal room conditions and will inevitably be a high carbon content alloy. In principle, any molten metal solvent for carbon which can enable diamond crystallization at such conditions may be employed.
  • the transition metals of the periodic table and their alloys may be included in such metals.
  • the predominant custom and practice in the prior art is to use the binder metal of hard metal substrates caused to infiltrate into a mass of diamond powder, after melting of such binders at the elevated temperature and pressure.
  • This is infiltration of molten metal at the macroscopic scale of the conventional PCD construction, i.e., infiltrating at the scale of millimeters.
  • the most common situation in the prior art is the use of tungsten carbide, with cobalt metal binders as the hard metal substrate. This inevitably results in the hard metal substrate being bonded in-situ to the resultant PCD.
  • Successful commercial exploitation of PCD materials to date has been very heavily dominated by such custom and practice.
  • PCD constructs which use hard metal substrates as a source of the molten metal sintering agent via directional infiltration and the bonding in-situ to that substrate, are referred to as “conventional PCD” constructions or bodies.
  • FIG. 2 is a schematic diagram of the infiltration process in a conventional PCD body with arrows indicating the direction and the long range of the infiltration through 2 to 3 mm of thickness of the PCD layer.
  • the arrows in the inset 11 indicate again that the range of infiltration transcends many diamond grains.
  • the PCD layer 6 in a conventional PCD body is normally of the order of 2 to 3 mm in thickness.
  • the substrate 7 is predominantly made of tungsten carbide/cobalt alloy.
  • the number 8 indicates approximately the direction of the infiltration of the cobalt infiltrant through the thickness of the PCD layer during the high pressure high temperature process.
  • the oval region 11 is at the interface between the carbide substrate and the PCD layer, and the inset of FIG. 2 shows schematically an expanded view of region 11 with the diamond grains in this region through which the long range infiltration of cobalt occurs.
  • the inset highlights the fact that the directional infiltration transcends many grains through the thickness of the PCD layer.
  • the diamond grains 9 and 10 may typically be of varying size in the body and could be made of multi modal mixes of diamond particles.
  • FIG. 1 is schematic diagram of the microstructure of PCD material showing the intergrown network of diamond grains with an inter-penetrating metallic network with facets occurring at the diamond-metal interfaces;
  • FIG. 2 is a schematic diagram of the infiltration process in a conventional PCD body with arrows indicating the direction and the long range of the infiltration through 2 to 3 mm of thickness of the PCD layer;
  • FIG. 3 is a schematic diagram of the very localised or short range movement of metal during the sintering of diamond particles to form an embodiment of PCD showing the diamond particles with well and homogeneously distributed, smaller metal particles;
  • FIG. 4 is a graph of cobalt content versus average grain size of the starting diamond particles for PCD sintered by the conventional route
  • FIG. 5 is a generalized flow diagram showing two alternative approaches of embodiments of the method and preferences, laid out in two columns, for combining diamond powders with appropriate metals to form a mass of particulate material, which after forming into a 3-dimensional semi-dense body is subjected to high temperature and pressure conditions to melt or partially melt the metal and partially re-crystallize the diamond to create the free standing PCD body;
  • FIG. 6 is a schematic diagram for the method of FIG. 5 column 2;
  • FIG. 7 is a cobalt, carbon binary phase diagram
  • FIG. 8 is a schematic representation of a diamond particle showing metal particles decorating the surface
  • FIGS. 9 a and 9 b are SEM micrographs of whisker-like crystals of cobalt carbonate decorating the surfaces of 2 micro meter sized diamond particles;
  • FIGS. 10 a and 10 b are SEM micrographs of cobalt metal particles decorating the surfaces of 4 micro meter sized diamond particles;
  • FIG. 11 is a TEM micrograph of a diamond particle decorated in cobalt metal particles together with a schematic diagram of the diamond surface;
  • FIG. 12 is two SEM micrographs of diamond particles decorated in cobalt particles and tungsten carbide
  • FIG. 13 is an SEM micrograph showing a multimodal size distribution of diamond particles which have been co-decorated in cobalt and tantalum carbide particles;
  • FIG. 14 is an embodiment of a 3-dimensional shaped PCD body intended for use in general applications
  • FIG. 15 is an SEM micrograph of mixed cobalt nickel carbonate crystals decorating 1 micron diamond particles.
  • FIG. 16 is an SEM micrograph showing 95% cobalt, 5% nickel alloy metal particles decorating the surfaces of 1 micron diamond particles.
  • a free standing, single volume of PCD material which is homogeneous and free of residual stress at a macroscopic scale greater than ten times the average grain size, where the coarsest component of grain size is no greater than three times the average grain size.
  • this PCD volume or body arises due to the absence of a bonded substrate of a dissimilar material to the PCD.
  • the absence of a substrate also means that the molten metal required for enabling the partial recrystallisation of the diamond particles to form the particle to particle diamond bonding does not arise from long range directional infiltration from such a substrate body. Rather, the required molten metal is provided solely by an initial homogeneous, intimate and accurate combination or mass of diamond particles and smaller, pure metal particles, grains or entities.
  • FIG. 3 is a schematic diagram of the very localised or short range movement of metal during the sintering of diamond particles in the PCD. It shows the diamond particles 13 with well and homogeneously distributed, smaller metal particles 12 . The metal movement is depicted by arrows 14 moving in all directions but only as far as neighbouring diamond particles.
  • the high purity of the diamond metal combination also ensured by embodiments of the methods described herein helps the generation of high homogeneity so that third phase precipitates, such as oxides and tungsten carbide and the like, may be avoided.
  • the free standing volume or body of homogeneous PCD material is not bonded in any way to other material bodies during manufacture, be they of a dissimilar material or of a different composition and structure of PCD. Macroscopic residual stresses cannot therefore be generated during return to room pressure and temperature at the end of the manufacturing process.
  • Such a free standing PCD body may thus be considered to be macroscopically stress free at a scale above which it is homogeneous, spatially invariant and considered to be made of one average property material. In the context of typical PCD materials, this scale may be considered to be greater than ten times the average grain size, where the coarsest component of grain size is no greater than three times the average grain size.
  • the average diamond grain size is about 10 to 12 micro meters and the maximum grain size is smaller than about 40 micro meters this scale may be considered to be above 120 micro meters. Where the average diamond grain size is about 1 micro meter where the maximum grain size is about 3 micro meters, this scale may be considered to be above 10 micro meters.
  • Some embodiments ensure or assist in the maintenance of diamond and metal homogeneity at each stage of manufacture of a free standing PCD body and employ short range permeation of molten metal during the sintering stage and thereby eliminate or substantially ameliorate the above-mentioned limitation. Consequently, the dimensions possible for the free standing, stress free PCD body in any orthogonal direction is not limited in such a way. Therefore, it is believed that any desired 3-dimensional shape may be generated, which is not possible in the conventional PCD prior art. Moreover, embodiments of the methods described herein may provide near net size and shape capabilities so that accurate non distorted free standing PCD bodies may be made.
  • PCD having valuable general shapes where one direction in the PCD body is significantly greater than any of the dimensions at right angles to it is believed to be possible.
  • columnar structures where the cross-sectional area perpendicular to the axis is circular (cylindrical shaped), elliptical or any regular or irregular polyhedral shape can be made.
  • the near net shape capability of some of the embodiments of the methods described herein may allow 3-dimensional solids having high degrees of symmetry to be made, such as spheres, ellipsoids (oblate and prolate) and regular solids.
  • the regular solids may include the five so-called “Platonic” solids, namely the tetrahedron, cube, octahedron, icosahedron and dodecahedron.
  • the thirteen semi-regular, so called “Archimedes” solids which include the cuboctahedron, truncated cube, truncated octahedron, truncated dodecahedron and truncated tetrahedron may also be made.
  • PCD bodies formed as conical and toroidal shapes may be made, together with polyhedral toroidal shapes. More generally, any irregular shape where the solid is bounded by one or more non-straight edge and one or more non-flat surface may be possible. All of the 3-dimensional solid shapes described above, be they of high symmetry or irregular may be modified by forming concave re-entrant surfaces. Such re-entrant surfaces may be bounded by flat polygonal faces, curved surfaces, irregular surfaces or any combination of these. Re-entrant surfaces may have particular value where the free standing body is required to be mechanically attached to a foundation or another body. For example, a circumferential groove may facilitate the use of a split ring for interlocking purposes.
  • Free standing PCD bodies made with in accordance with some embodiments of the method described herein may be made such that the largest dimension in any direction in the body may fall within the range 5 to 150 mm.
  • a free standing PCD body consisting of a right circular cylinder of 100 mm diameter and 100 mm long will have the largest dimension along a body diagonal of 141.4 mm.
  • a free standing PCD cube of edge length 85 mm which has a face diagonal of 120.2 mm and a body diagonal of 147.2 mm.
  • Another example of a small free standing PCD right circular cylinder which has its largest dimension within the quoted range has a diameter of 4 mm and a length of 4 mm and a body diagonal of 5.66 mm.
  • the accuracy in diamond-to-metal ratio characteristic of some embodiments of the methods described herein results from the metal or alloy being smaller than the diamond particle sizes, and being homogeneously distributed and associated with each diamond particle. This is particularly true for the method where the metal(s) or alloy(s) of choice are decorated onto or associated with the surface of each individual diamond particle of the starting diamond powder.
  • the metal(s) or alloy(s) of choice are decorated onto or associated with the surface of each individual diamond particle of the starting diamond powder.
  • the molten metal permeates the interstices between the diamond particles to a very limited range between the surrounding particles. This ensures that the chosen diamond to metal ratio is constant and invariant across the dimensions of the free standing PCD body and homogeneous at a macroscopic scale.
  • the scale above which this homogeneity and invariance of composition occurs is dependent upon the grain size distribution of the PCD material and is smaller for smaller average grain sizes.
  • the material can be considered to be homogeneous and spatially invariant above about 10 micro meters.
  • the macroscopic scale above which the PCD material is considered to be spatially invariant may be defined as at a scale greater than 10 times the average grain size, where the largest grains are no more than 3 times the average grain size.
  • the accuracy of the alloy composition in some embodiments described herein may be achievable as a consequence of the use of molecular precursors for the chosen metals in the methods described herein.
  • Some of the molecular precursors such as nitrate or carbonate salts of the metals may be made as mixed crystals or solid solutions. This is possible in the cases where the metal salts are isomorphous, i.e., having the same crystallographic structure. In particular, this is true for the carbonates of some transition metals such as iron, nickel, cobalt and manganese.
  • the accuracy of the specifically chosen metallic element ratio may be determined by easily provided concentration ratios of the solutions of the source compounds of the chosen metals.
  • concentration ratios of the solutions of the source compounds of the chosen metals One of the examples of this is to create a combined mixed solution of metal nitrates in water and then to precipitate a mixed carbonate precursor for the chosen alloy by reaction with sodium or ammonium carbonate solutions.
  • the use of mixed molecular precursors in this way enables the chosen metal elements to be combined at an atomic scale.
  • the conventional approach to PCD manufacture necessarily involves alloying by virtue of melts, flowing and diffusing together which always results in spatial variation and inaccuracy.
  • Precursor compounds which may be dissociated and/or reduced to metals and alloys are readily available for nearly all the metals of the periodic table. Those precursors which can be reduced to metals or metal carbides by reaction with carbon may be preferred.
  • the metals of Group VIIIA of the periodic table can be exploited individually or in fully alloyed combinations.
  • the metals chosen wholly or in part must however be capable of facilitating diamond crystallization in order to create the necessary diamond particle to particle bonding for PCD.
  • An important implication of this is that the resultant metallic network of the PCD material has carbon in solid solution usually to a maximum level as expressed in appropriate metallurgical phase diagrams.
  • metallic elements which readily form stable carbides will also be present in the metallic network as carbide components.
  • the metal alloys exploitable in PCD are the high carbon versions of such metals.
  • the free standing PCD bodies of some embodiments described herein due to the high homogeneity and accuracy of composition may thus exploit the special properties of highly specific chosen compositions.
  • the metallic network may be chosen to be made from controlled expansion alloys which have highly specific elemental ratios.
  • the thermo elastic properties of the metallic network may therefore be chosen to be specific from a wide range but, due to the homogeneity, be the same at all parts of the free standing PCD body.
  • the range of linear coefficient of thermal expansion for the metallic network extends from magnitudes typical of elements such as cobalt (13 ppm ° K ⁇ 1 at room temperature) to that typical of low expansion alloys like the high carbon version of Invar (Fe, 33% Ni, 0.6% C, about 3.3 ppm ° K ⁇ 1 at room temperature, ref 4).
  • the diamond network will be generally compressively stressed and the metallic network generally under tension.
  • the magnitude of this micro residual stress may be considered to be high when the linear coefficient of expansion of the metallic network is 10 to 14 ppm ° K ⁇ 1 , medium for a linear coefficient of expansion of 5 to 10 ppm ° K ⁇ 1 and low for less than 5 ppm ° K ⁇ 1 .
  • these micro residual stresses sum to zero, resulting in the macroscopic residual stress being considered to be zero and the free standing PCD body itself to be macroscopically stress free.
  • PCD bodies where the micro residual stress in the metallic network has an overall compressive nature form some embodiments and are now disclosed.
  • micro residual stresses play a significant role in crack initiation and local crack coalescence during mechanical applications of PCD materials. This may be considered as a key aspect of wear behaviour at the particle to particle level. Materials with a low propensity of micro cracking may hence be developed using the approach and methods described herein.
  • the ability to independently choose and pre-select the metal content and metallurgical type of the PCD material for the purpose of micro structural stress management as discussed above is an example of an important and distinct character of some embodiments, namely, the ability to independently choose and control the structural and compositional variables.
  • the method of some embodiments described herein allows independent choices and control of these variables and also the homogeneity of the end products to be specifically engineered to be high.
  • the metal content, metal type, diamond size and size distribution may be independently chosen and controlled.
  • the metal content is restricted to about 12 to 14 volume percent.
  • some embodiments described herein provide for the metal content to be chosen independently to the metal type and be anywhere in the range from about 1 to 20 percent.
  • the metal content may be chosen anywhere in the range from about 1 to about 20 percent.
  • the metal content for conventional PCD material being restricted to around and close to 9 volume percent, as illustrated in FIG. 4 , no longer applies.
  • the metallic network may be chosen to be most combinations and permutations of the metals of the periodic table provided that diamond crystallization can be facilitated by such metals, which also means that the alloys all have a high carbon content. This choice is made completely independently of average grain size, grain size distribution and diamond to metal ratio. Clearly, a greatly extended range of PCD material types with their attendant properties can now be accessed. Yet another feature of some embodiments described herein is that the element tungsten will be absent unless deliberately included. This is in contrast to the dominant custom and practice of the conventional prior art PCD approach where tungsten carbide/cobalt hard metal substrates are used which inevitably result in tungsten being inhomogeneously incorporated as tungsten carbide precipitates in the PCD layer.
  • Some embodiments of the methods described herein assist in allowing the incorporation of tungsten carbide as an added phase at controllable and homogeneous levels if such compositions are chosen.
  • PCD compositions free of tungsten may, however, readily be made.
  • the metals and alloys which are capable of facilitating diamond crystallization after melt include any of and any combined permutations or alloys of the transition metals of the periodic table whereby at least one metal does not form stable carbide compounds at conditions of temperature and pressure appropriate for diamond crystallization.
  • Typical of these latter metals and preferred for diamond crystallization processes are the Group VIIIA metals of the periodic table such as iron, nickel, cobalt and also the Group VIIA metal manganese.
  • Transition metals which form stable carbides under typical diamond re-crystallization from metal solutions conditions include tungsten, titanium, tantalum, molybdenum, zirconium, vanadium, chromium and niobium.
  • Some embodiments described herein allow the metallic network in the PCD body to be accurately chosen combinations of iron, nickel, cobalt or manganese with the carbides of these elements.
  • cobalt, tungsten carbide (WC) combinations ranging from high cobalt content to low cobalt content may be provided by some embodiments of these methods.
  • a further feature some embodiments occurs as a result of the absence of macroscopic residual stress, in that manufacturing pressure and temperature conditions may be widely chosen as undesirable residual stress distributions from such pressure and temperature choices does not occur.
  • the conventional PCD approach suffers from significant increases in residual stress distributions as higher pressures and temperatures are used causing a high incidence of cracking and fracture of the PCD parts during manufacture.
  • the approach of some embodiments described herein may allow the ready beneficial use of higher pressures and temperatures.
  • the benefits may include increased intergrowth of diamond particles and associated property improvements such as increases in hardness, strength and thermal properties with increased diamond to metal ratio.
  • the convenience of using increased pressures and temperatures may allow fully dense PCD material to be achieved.
  • the approaches and means used to make the mass or combination of diamond powder and appropriate metals and alloys for subsequent sintering of the diamond particles at high pressure and temperature may provide homogeneity in diamond size distribution, diamond to metal distribution and metal composition. This homogeneity of the powder mass or combination may then provide for the homogeneity of the final sintered PCD material body. Further, this may be facilitated if, preferably, the form of the metals or metal alloys is of metal particles, grains or entities which are smaller than the size of the diamond particles for each chosen size or size range of diamond particles required to produce PCD with a chosen desired grain size distribution.
  • FIG. 5 is a generalized flow diagram showing alternative approaches and preferences for combining diamond powders with appropriate metals to form a mass of particulate material which, after forming into 3-dimensional semi-dense so-called “green” bodies, is subjected to high temperature and pressure conditions to melt or partially melt the metal and partially re-crystallize the diamond to create the free standing PCD bodies.
  • Methods according to one or more embodiments of creating a starting mass of combined diamond particles and smaller metal(s) or alloy(s) make use of precursor compounds, which may be dissociated or reduced to form the sufficiently pure metals and alloys by heat treatment in controlled environments.
  • precursor compounds which may be dissociated or reduced to form the sufficiently pure metals and alloys by heat treatment in controlled environments.
  • environments include vacuum or appropriate gases which have reducing gases present such as hydrogen or carbon monoxide and the like.
  • These precursors include compounds such as salts, oxides and organometallic compounds of the transition metals or any chemical compound which can be dissociated and or reduced to yield at least one of the required metals.
  • these precursors may be mixed.
  • Ionic compounds such as salts which can be dissociated and/or reduced to form pure metals may be examples of candidates for precursors.
  • examples of some such salts are nitrates, sulphates, carbonates, oxalates, acetates and hydroxides of the transition metals.
  • oxalates of cobalt and nickel, CoC 2 O 4 and NiC 2 O 4 which decompose to the metal in inert atmosphere, such as nitrogen, at very low temperatures and above such as 310 and 360° C., respectively (Ref 1).
  • Such oxalates may be used in hydrated form, e.g. crystals of CoC 2 O 4 .2H 2 O and NiC 2 O 4 .2H 2 O or dehydrated form.
  • Nitrate salts in particular cobalt(II) nitrate hexahydrate crystals, Co(NO 3 ) 2 .6H 2 O, nickel nitrate hexahydrate crystals, Ni(II) (NO 3 ) 2 .6H 2 O and ferrous iron(II) nitrate hexahydrate crystals, Fe(NO 3 ) 2 .6H 2 O, respectively, may, in some embodiments, be preferred as crystallized precursors for the specific metals.
  • Such nitrate crystals are easily dehydrated and dissociated at low temperatures approaching 200° C. and reduced to the pure metals above temperatures as low as about 350° C. in hydrogen containing gaseous environments (Ref. 2 and 3).
  • Alloy compositions may be obtained by mixing the salts or by the use of mixed metal single compounds such as mixed salts.
  • mixed metal single compounds such as mixed salts.
  • One advantage of using such mixed salts may be that, on dissociation and/or reduction to the metallic state, the metals will already be mixed at the atomic scale, engendering maximum homogeneity in regard to alloy composition.
  • Carbonates are also excellent precursors for metals such as iron, nickel, cobalt, copper and manganese. On thermal dissociation and reduction these salts form particularly finely sized metals, often down to a few tens of nanometers.
  • metals such as cobalt, nickel, iron, manganese or copper
  • metals which form stable carbides during decomposition/reduction and/or diamond sintering such as tungsten, molybdenum, chromium, tantalum, niobium, vanadium, zirconium, titanium and the like
  • a useful approach is to use ionic compounds where the former metals form the cation and the latter carbide forming metals form part of the anion, such as in tungstates, molybdates, chromates, tantalates, niobates, vanadates, zirconates and titanates, respectively.
  • Some important examples of such compounds are cobalt tungstate, CoWO 4 , nickel molybdate, NiMoO 4 and cobalt vanadate, Co 3 (VO 4 ) 2 , respectively.
  • Intermetallic compounds such as CoSn may also be made by dissociation/reduction of precursors such as cobalt stannate, CoSnO 3 .
  • oxides which may be used include ferrous and ferric oxide (Fe 2 O 3 and Fe 3 O 4 ), nickel oxide (NiO), cobalt oxides (CoO and Co 3 O 4 ).
  • the latter oxide, Co 3 O 4 may be produced as micro meter sized aggregates of 20 to 100 nm particles by the decomposition of cobalt carbonate in air at low temperatures such as 300 to 400° C. For final alloy formation, these precursors may be mixed.
  • precursor compounds for the metal(s) or alloy(s) may be crystallized from solution in liquids where the diamond powder is present as a solid suspension, FIG. 5 column 1.
  • Some precursor compounds are soluble in solvent liquids such as water or alcohols and may be crystallized from such solutions by reduction of temperature and/or evaporation of the solvent or protocols known in the art of crystallization from solution, where suitable degrees of supersaturation and or seeding may be exploited.
  • Stable suspensions of desired diamond particle size distributions anywhere in the range of 0.1 to greater than 30 micro meters may be obtained when in water or alcohol, particularly when the suspension is vigorously stirred. After appropriate settling and decantation followed by drying procedures, a combination of solid precursor(s) for the metal and diamond results. The crystallization of the precursor is organized such that the particle or crystal size is smaller than that of the diamond powder. Subsequently, dissociation and/or reduction of the precursor by heat treatment in vacuum or reductive gases generates a mass of diamond and smaller sized metal particles, grains or entities. Approaches where diamond suspensions are used, particularly when they are continuously stirred, may engender excellent homogeneous mixing with crystallized precursors.
  • the liquid suspension medium for the diamond and solvent for the precursor compounds may be water or alcohols such as ethanol and the like or any appropriate and convenient liquid.
  • preferred precursors for the metals are salts and in particular nitrates. This is because all metal nitrates have a high solubility in water and may readily be thermally dissociated and/or reduced to the pure metal by low temperature heat treatment.
  • cobalt(II) nitrate hexahydrate crystals Co(NO 3 ) 2 .6H 2 O, nickel nitrate hexahydrate crystals, Ni(II) (NO 3 ) 2 .6H 2 O and ferrous iron(II) nitrate hexahydrate crystals, Fe(NO 3 ) 2 .6H 2 O, respectively, may be used, for example, as crystallized precursors for the specific metals.
  • Such nitrate crystals are easily dehydrated and dissociated at low temperatures approaching 200° C. and reduced to the pure metals above temperatures as low as about 350° C. in hydrogen containing gaseous environments (Ref 2 & 3).
  • many of the metal nitrates may be co-crystallized as mixed crystals whereby atomic scale mixing of extremely accurate alloys may be achieved on dissociation and reduction to the metallic state.
  • oxalates M x (C 2 O 4 ) y , x and y being dependent upon the valency of the metal M, as the anion is (C 2 O 4 ) 2 ⁇ .
  • oxalate salts which may be used include cobalt oxalate dehydrate crystals, Co(II)C 2 O 4 .2H 2 O, nickel oxalate dehydrate crystals, Ni(II)C 2 O 4 .2H 2 O and ferrous iron oxalate dehydrate crystals, Fe(II)C 2 O 4 .2H 2 O.
  • Ferric oxalate pentahydrate crystals Fe(III) 2 (C 2 O 4 ) 3 .5H 2 O may also be crystallized and used in this approach. These compounds may be very easily decomposed and/or reduced to the pure metal at low temperatures (Ref 1).
  • Transition metal acetate crystals may also be used in this approach, such as cobalt acetate quadrahydrate, Co(II)(C 3 H 3 O 2 ) 2 .4H 2 O, nickel acetate quadrahydrate, Ni(II)(C 3 H 3 O 2 ) 2 .4H 2 O crystals and ferrous iron acetate quadrahydrate, Fe(II)(C 3 H 3 O 2 ) 2 .4H 2 O crystals.
  • the precursor is significantly insoluble in the chosen suspension liquid.
  • the reactants to form the precipitated precursor are introduced into the diamond suspension by adding solutions of soluble compounds. One or more of these solutions is a source of the desired metal or metals.
  • FIG. 6 is a schematic diagram for this approach and illustrates a solution of a compound which is a source of metal atoms or ions, 16 , is simultaneously added together with a solution of reactants, 17 , to a continuously stirred suspension of diamond powder, 18 .
  • the metal source compound and reactant from solutions 16 and 17 react to form precipitate crystals or compounds which nucleate and grow on the diamond particle surfaces.
  • These crystals or compounds then decorate the diamond surfaces and are precursor(s) for pre-selected metal particles.
  • a representative diamond particle, 19 is illustrated with a precursor compound, 20 , which decorates the particle surface.
  • Notable examples of this approach may have the feature of the nucleation and growth of the precursor compound on the surface of the diamond particles.
  • the precursor compound(s) for the metal are attached to the diamond surfaces and may be said to decorate said surfaces.
  • the precursor is discretely distributed and does not form a continuous coating of the diamond particle surfaces.
  • Some precursors may however form continuous coats on the diamond surfaces but on dissociation and reduction to the metallic state, the metal particles are discrete and discontinuously distributed and decorate the diamond surfaces. Examples of the latter are amorphous oxides formed by reaction of metal alkoxides with water, elaborated upon below.
  • the surface chemistry of the diamond particles may be deliberately chosen and produced to suit the nucleation of the precursor(s).
  • the precursor compound being precipitated has an oxy-anion such as CO 3 2 ⁇ or OH ⁇ , or is formed by polycondensation
  • hydrophilic diamond surface chemistries based upon oxygen species such as ⁇ OH, —C ⁇ O or —C—O—C— and the like are appropriate.
  • Means of accentuating such diamond surface chemistries are well known in the art and include high intensity ultrasound treatment of the diamond in water.
  • FIG. 6 includes a schematic representation of a diamond particle with the surface decorated in a crystalline precursor compound.
  • the precursor compound being a surface decorant or coating means that the carbon at the diamond surface in contact with the precursor may act as an efficient reducing agent for the metal precursor compound on subsequent heat treatment.
  • This carbothermal reduction of the precursor may be used solely or in conjunction with other dissociative or reductive steps such as the use of hydrogen gas as reducing agent.
  • the resultant metal will take in carbon from the diamond surface and contain carbon in solid solution.
  • Stable carbides may also form at such conditions.
  • the amount of carbon in solid solution in the metal decorant is highly dependent upon the temperature chosen for dissociation and reduction of the precursor.
  • FIG. 7 is the binary cobalt, carbon phase diagram.
  • the line labeled AB is the solid solubility limit of carbon in solid face-centred-cubic cobalt. If the dissociation, reduction of a precursor for cobalt to obtain the metal is carried out at 700° C., the carbon content of the resulting cobalt metal will be given by this line at 700° C., namely about 0.2 atomic percent carbon, similarly if the dissociation, reduction is carried out at 1050° C., the carbon content of the cobalt will be about 0.8 atomic percent carbon. On quench to room conditions these carbon contents may be metastably maintained. Thus the carbon content of the resultant metal on the diamond surfaces may be chosen and predetermined.
  • the carbon in solid solution in the metal may diffuse through the metal decorating the surface and progressively transport carbon from the diamond surface and come out of solution at the metal surface, forming a deposit of non-diamond carbon.
  • chosen and controlled predetermined amounts of amorphous and or nano-crystalline non-diamond carbon may be generated on the metal surfaces.
  • This non-diamond carbon component of the starting diamond metal particulate mass may contribute to the efficient crystallization of diamond which bonds the diamond particle or grains together in the final PCD body.
  • Superior, especially well inter-grown diamond networks may be produced by control of such a non-diamond carbon component of the starting mass.
  • Lower temperature conditions for short periods may also be chosen, guided by the appropriate metal, carbon phase diagram so that the non-diamond carbon is low or absent.
  • FIG. 8 shows schematic representations of a diamond particle 21 and metal particles decorating the surface 22 thereof.
  • the metal particles may comprise grains or other entities without and with significant amounts of non-diamond carbon.
  • the metal particles may have their surfaces covered in amorphous non-diamond carbon, 23 , dependent on the choice of dissociation, reduction temperature. Temperatures chosen near A in FIG. 7 do not result in detectable non-diamond carbon. Temperatures chosen near B in FIG. 7 , result in significant formation of non-diamond carbon, which cover the metal particles.
  • a character of the metal decorant particles, grains or entities which result from this preferred approach is that they are much smaller than the diamond particles themselves and do not form a continuous metal coating.
  • the metal decorants are typically from about 10 to just over 100 nm in size. This may allow very fine, so called sub-micron diamond particle sizes, from 0.1 to 1 micro meter to be accurately and homogeneously combined with chosen metals. This may provide a means of making PCD bodies of extremely fine diamond grain size less than 1 micro meter.
  • a further benefit of this diamond suspension technique is that it may be readily and conveniently scaled to that required by commercial PCD manufacturing, where batch quantities of several kilograms may be required. This may be done by appropriate choice of suspension vessel sizes in conjunction with, where necessary, heat treatment furnace designs capable of continuous operation.
  • Cobalt is the historically dominant metal used in PCD material.
  • a very convenient source solute for cobalt is crystalline pure cobalt nitrate salt, Co(NO 3 ) 2 .6H 2 O. This is due to cobalt nitrate's very high solubility in both water and ethyl alcohol, which are possible solvents and suspension liquids for some embodiments of the method.
  • Cobalt nitrate in solution reacts with sodium or ammonium carbonate solution, Na 2 Co 3 or (NH 4 ) 2 CO 3 , respectively to precipitate cobalt carbonate crystals, CoCO 3 , as indicated in equation (1) below for the sodium carbonate case.
  • the nitrate solutions of any of the transition metals of the periodic table may be reacted with sodium or ammonium carbonate solution to precipitate and decorate the surfaces of diamond particles in suspension with corresponding water insoluble metal carbonates.
  • the reaction with different transition metal nitrate solutions may be carried out sequentially or simultaneously.
  • FIGS. 9 a and 9 b are scanning electron microscope (SEM) images of a 2 micro meter diamond particle which has been decorated in very fine, approximately 100 nm long, whisker like cobalt carbonate crystals. Whisker-like crystals of cobalt carbonate are shown as decorating the surfaces of 2 micro meter sized diamond particles.
  • Cobalt carbonate is a precursor compound for cobalt metal.
  • such cobalt carbonate decorated diamond particles may be heated in, for example, a flowing gas mixture of 10% hydrogen in argon, at a constant temperature chosen in the range 500 up to 1320° C., for time periods of from several tens of minutes to a few hours. If the temperature is maintained below about 850° C. for a chosen short time, no non-diamond carbon can be detected.
  • FIGS. 10 a and 10 b are SEM images of 4 micro meter sized diamond particles decorated in about 22 weight % (10 volume %) cobalt after reduction in 10% hydrogen argon gas mixture at 850° C.
  • the cobalt metal decorating particles or grains vary from about 10 to 120 nm in size. In this embodiment, no non-diamond carbon could be detected with SEM or transmission electron microscope (TEM) techniques.
  • FIG. 11 is a TEM micrograph of a diamond particle decorated in cobalt metal particles, 26 , together with a schematic diagram of the diamond surface, 25.
  • Each cobalt metal particle or grain, 26 is surrounded by a non-diamond carbon halo, 27 on a hydrogenated diamond surface, 25.
  • the non-decorated portion of the diamond surfaces will be hydrogen terminated after such a heat treatment as
  • the schematic diagram of FIG. 11 shows nano cobalt particles or grains decorating the surface of a diamond particle after reduction of cobalt carbonate decorant at 1050° C. for two hours in flowing 10% hydrogen/argon gas mixture.
  • the hydrogen termination of the diamond surface where the metal decorant is absent is a useful feature of the some embodiments of the method when hydrogen heat treatment is included.
  • Ni(OH) 2 nickel hydroxide, Ni(OH) 2
  • Ni(OH) 2 nickel hydroxide, Ni(OH) 2
  • equation (2) nickel hydroxide
  • the precipitative approach may also be applied to precursors which combine metals such as iron, nickel, cobalt, manganese, copper and the like as cations with the metals of the periodic table which may readily form stable carbides such as tungsten, molybdenum, chromium, tantalum, niobium, vanadium, zirconium, titanium and the like, as oxy-anions.
  • These precursors may include tungstates, molybdates, chromates, tantalates, niobates, vanadates, zirconates and titanates.
  • cobalt tungstate Co(WO 4 ) 2 may be decorated onto diamond particle surfaces by the reaction of cobalt nitrate solution with sodium tungstate solution in water as indicated in equation (3).
  • An alternative chemical protocol to introduce tungsten is to use the reaction of ammonium paratungstate (NH 4 ) 10 W 12 O 41 solution with dilute mineral acids such nitric acid, HNO 3 to precipitate tungstic oxide, W0 3 as surface decorant, which in turn is readily reduced in the presence of diamond to form tungsten carbide particles.
  • Precipitation of carbonates after that of the tungstic oxide, such as cobalt carbonate using equation (1), may be done to co-decorate the diamond surfaces.
  • FIG. 12 Two SEM micrographs are given in FIG. 12 showing the surface of diamond particles of about 2 micro meters in size, decorated in both cobalt, 28 , and tungsten carbide, 29 , particles after reduction of such a co-decoration in 10% hydrogen, argon flowing gas mixture at 1050° C.
  • the precursor used for the cobalt was cobalt carbonate and the precursor used for the tungsten carbide was tungstic oxide.
  • TEM microscopy also detected significant amounts of non-diamond, mainly amorphous carbon forming a covering on the cobalt particles after such furnace conditions. Very similar chemical protocols may be used to create decorants involving molybdenum carbides.
  • a preferred chemical route is to react dry alcoholic solutions of the metal alkoxides with water, with the diamond powder suspended in alcohol. When this is done, amorphous, micro-porous coats of the metal oxide form on the diamond particles. On subsequent heat treatment these oxide coats form discrete decorations of metal carbide on the diamond particle surfaces.
  • a general formula for the metal alkoxides is M(OR) n , where n is dependent upon the valency of the metal M and R is a alkane group, such as methyl, —CH 3 , ethyl, —CH 2 CH 3 , isopropyl, —C 3 H 7 and the like.
  • the metal alkoxides reaction with the water to yield hydroxides, as is given in equations (4), which then undergo polycondensation reactions to form the amorphous oxide coats as in equation (5).
  • Ta 2 O 5 An example reaction for amorphous tantalum oxide, Ta 2 O 5 is given in equation (6) where tantalum ethoxide, Ta(OC 2 H 5 ) 5 is reacted with water in ethyl alcohol, C 2 H 5 OH.
  • precursors for metals such as cobalt, nickel, iron, manganese and the like, such as carbonates or hydroxides, may be precipitated into and onto the oxide coats using the chemical reactions already indicated. Cermet or hard metal like compositions of combined decorations of these metals with carbides may then be formed by appropriate heat treatment in reducing environments.
  • FIG. 13 shows an SEM micrograph of a multimodal diamond powder made up of fine diamond particles (about 2 micro meters in diameter) and coarser particles (from about 15 to 30 micro meters in diameter), which has been decorated in 5.3 weight % tantalum carbide (TaC) particles together with 3 weight % cobalt particles.
  • the precursor for the TaC was amorphous Ta 2 O 5 deposited onto the diamond surfaces by reaction (6). After settling, washing and drying procedures, the diamond powder was then co-decorated with cobalt carbonate crystals using the reaction of equation (1). Subsequently the combined precursors were reduced to form the TaC, cobalt metal co-decoration of FIG. 13 by heat treatment in flowing 5% hydrogen, nitrogen gas at 1100° C. for 3 hours. It may be seen in FIG. 13 that both the TaC particles 31 which appear bright in appearance and the cobalt metal particles 30 which appear duller in appearance are very much smaller than the diamond particles and homogeneously cover both the coarse and fine diamond particles.
  • Free standing PCD bodies may then be made from masses of diamond particles such as these, with their decorations of metal, metal carbide combinations.
  • the resultant metal, metal carbide network of the PCD material may have cermet or hard metal carbide like compositions.
  • Some embodiments of such compositions include WC/Co, TaC/Co and TiC/Ni.
  • any of these chemical reactions to form the precursor compound decorants on the diamond particle surfaces may be done in sequence and applied to the pre-selected diamond powder as a whole or to any part or component of the diamond powder in appropriate suspension media.
  • the diamond powder components may be based upon mass fractions or upon size, size distribution or any desired combination of these.
  • the part or component of the desired diamond size distribution is first suspended in the liquid medium and the chosen chemical reaction protocol(s) to decorate that component with chosen precursor(s) carried out. Subsequently, the remaining diamond powder component or part is added and suspended.
  • the act of suspension and attendant vigorous stirring provides an efficient means of homogeneously mixing the decorated and undecorated portions of the diamond powder.
  • chosen pre-selected components of the diamond powder may be decorated in chosen metal with the other components remaining undecorated after subsequent dissociation/reduction of the precursor(s) to the metal(s).
  • differing amounts of the same precursor may be decorated onto different mass and/or size fractions of the diamond powders by sequential adding of the components to the suspension, reaction vessel.
  • different amounts of and/or types of precursor(s) may be decorated on chosen diamond powder components in separated suspension vessels. Again a final combination of the suspensions can provide efficient homogeneous mixing of these components.
  • any of the diamond powder fractions or components may be made up of diamond particles differing in respect to diamond type.
  • Diamond particles of differing type are distinguished here in regard to the variation in structure and/or quantity of lattice defects known in the art.
  • nitrogen related lattice defects are exemplary, which are known to affect the material properties of diamond.
  • a convenient way to differentiate diamond type is to use natural diamond as opposed to standard synthetic diamond, natural diamond having typically aggregated nitrogen lattice defects as compared to standard synthetic diamond which contains single atoms of nitrogen substituting for carbon atoms at levels typically of about 100 ppm.
  • These means of associating different amounts and/or different metal compositions with different diamond fractions or components may provide a highly accurate and versatile way of manipulating the diamond sintering mechanisms at the local scale of the diamond particles and in turn engendering manipulation of structure and composition at such a scale. For example, if certain fractions remain free of metal during initial application of load and heat in the high pressure apparatus, diamond particle, point to surface contact for the particles of such fractions can be un-fettered by metal decoration leading to enhanced plastic deformation of such particles. This in turn may be possible to facilitate local enhanced diamond to diamond bonding. Further it may be possible to associate immovable “unmelted” particles with some diamond particle fractions and not others.
  • metal carbide particles such as tungsten carbide, titanium carbide, tantalum carbide and the like may be decorated onto and associated only with a particular size fraction of the diamond.
  • a vast number of PCD free standing body embodiments with novel compositions, structures and properties may in this way be generated using such prepared decorated diamond powder, metal combinations or masses.
  • the homogeneous mass of diamond and metal is consolidated to form a so-called “green body” of desired size and 3-dimensional shape.
  • Means of forming a green body include simple die set compaction, isostatic compaction, gel casting, injection moulding and the like and any other technique or procedure known in the art. Where isostatic compaction is used, hot isostatic procedures are preferred due to superior strength of the green bodies occurring. Preferences amongst such means to produce green bodies may be determined by the degree to which each technique can maintain general compositional and special homogeneity. Temporary organic binders such as methyl cellulose, polyvinyl alcohol, polyvinyl bitherol and the like may be employed to aid with green body integrity and of sufficient strength for practical handling.
  • the homogeneous green body is then encapsulated such that it may be contained and isolated from the pressure and temperature media and structures of high pressure and high temperature cells, capsules or reaction chambers as well known in the art of polycrystalline diamond manufacture.
  • the 3-dimensional shape of the desired PCD body is geometrically simple canisters made from refractory metals may be used.
  • appropriate canisters may be moulded from refractory metals.
  • the encapsulation material or metal canisters are preferably organised so that they may be evacuated and sealed again as had been established and is well known in the art.
  • Removing atmospheric gases from the porosities of the green body and sealing the green body's encapsulation materials to maintain a vacuum in the porosities is a preference.
  • Prior to the sealing of the encapsulation materials or canisters or temporary organic binders which may have been employed in forming the green bodies must be removed by procedures such as heat treatment and the like.
  • the green bodies in their sealed encapsulations are then assembled into a cell or capsule comprising pressure and temperature transmitting media and heating element structures as known in the art.
  • the design of the cell or capsule is chosen so that pressure and temperature gradients experienced by the green body at its sintering conditions are minimised.
  • Low shear strength pressure transmitting materials such as ionic salts often combined with ceramic powders may be used, for example, sodium chloride combined with zirconia, ZrO 2 . These measures assist in enabling the homogeneity of the structure and composition of the green body to be translated into corresponding homogeneity of the PCD body on sintering.
  • the pressure and temperature time cycle may be chosen so that simultaneous and or symmetrical melting of the metal component in the green body occurs.
  • a further precaution to engender stress free and crack free standing PCD bodies may be to release the pressure during the end phase of the manufacturing cycle with the maintenance of sufficient temperature to maintain the pressure transmitting media of the cell or capsule in as plastic a state as possible.
  • the homogeneity of the green body together with the precautions outlined above is necessary so that the shrinkage during sintering of the diamond particles is equal in all orthogonal directions. In this way, the pre-selected 3-dimensional shape of the green body may be maintained and translated to the final free standing PCD body.
  • the degree and magnitude of the equi-directional shrinkage for each variant or embodiment of PCD material and body may be empirically determined.
  • This feature of net or near net size and shape may provide practical and commercial viability and attractiveness as further sizing and shaping is minimized or not required.
  • the green bodies generated by the above methods are subjected to high pressure, high temperature conditions for appropriate times to cause sintering of the diamond particles and form the free standing PCD bodies.
  • Each specific chosen metallic composition may require specific temperature, pressure and time cycles to be determined empirically such that the re-crystallized diamond is of good quality crystal and is largely defect free.
  • Typical pressure and temperature conditions are in the range of 5 to 15 GPa and in the range of 1200 to 2500° C. respectively.
  • pressures in the range 5.5 to 8.0 GPa along with temperatures in the range 1350 to 2200° C. are used.
  • PCD free standing, macro residual stress free, bodies each comprising an intergrown diamond network with a monomodal, mean grain size of close to 1 micro meter with an inter-penetrating metallic network made up of independently pre-selected alloy made up of 95 weight % cobalt and 5 weight % nickel were manufactured.
  • the overall diamond content was pre-selected independently of the diamond size distribution and alloy composition to be about 93 volume % with the metal being a corresponding 7 volume %.
  • the PCD body was a right cylinder 13 mm in diameter and 8 mm long.
  • the method as outlined in FIG. 5 column 2 was used whereby the precursor for the metallic component of the PCD body was reactively created in a water liquid suspension of starting diamond particles and was caused to nucleate and grow on the surfaces of the starting diamond particles. The following sequential steps and procedures were carried out in order to so manufacture this PCD free standing body.
  • the mixed cobalt nickel carbonate precursor nucleated and grew on the diamond particle surfaces and formed a discrete set of particles decorating the surfaces.
  • the sodium nitrate product of the reaction, equation 7, being highly soluble in water was then removed by a few repeated cycles of decantation and washing in de-ionised water. After a final wash in pure ethyl alcohol the precursor decorated diamond powder was dried under vacuum at 60° C.
  • the dried powder was then placed in an alumina ceramic boat with a loose powder depth of about 5 mm and heated in a flowing stream of argon gas containing 5% hydrogen.
  • the top temperature of the furnace was 1050° C. which was maintained for 2 hours before cooling to room temperature.
  • This furnace treatment dissociated and reduced the mixed cobalt-nickel carbonate to form alloy particles decorating the surfaces of the diamond particles. In this way it was ensured that the alloy metal particles were always smaller than the diamond particles with the alloy being homogeneously distributed.
  • FIG. 15 is an SEM micrograph showing the fine cobalt nickel carbonate crystals decorating the 1 micron diamond particle surfaces. It may be seen that the precursor crystals or particles are all significantly smaller than the diamond particles.
  • FIG. 16 is an SEM micrograph showing the alloy metal particles decorating the diamond particle surfaces.
  • the alloy metal particles comprise 95% cobalt, 5% nickel alloy metal particles which are shown as decorating the surfaces of 1 micron diamond particles.
  • the conditions of the heat treatment also caused amorphous non-diamond carbon to form at the surfaces of the cobalt-nickel alloy particles.
  • the resultant powder mass had a black appearance.
  • the powder mass was stored under dry nitrogen in an air-tight container.
  • PCD free standing, macro residual stress free, bodies each comprising an intergrown multimodal diamond network where the grain size distribution extends from about 2 micro meters to about 30 micro meters with a mean grain size of close to 10 micro meter together with an inter-penetrating metallic network made up of pure cobalt were manufactured.
  • the overall diamond content was pre-selected independently of the diamond size distribution and metal composition to be about 91 volume % with the metal being a corresponding 9 volume %.
  • the PCD body was a right cylinder 16 mm in diameter and 16 mm long.
  • the method outlined in FIG. 5 column 2 was used whereby the precursor for the metallic component of the PCD body was reactively created in a water liquid suspension of starting diamond particles and was caused to nucleate and grow on the surfaces of the starting diamond particles. The following sequential steps and procedures were carried out in order to so manufacture this PCD free standing body.
  • 100 g of diamond powder was suspended in 2.5 litres of de-ionised water.
  • the diamond powder comprised 5 separate so-called monomodal diamond fractions each differing in average particle size.
  • the diamond powder was thus considered to be multimodal.
  • the 100 g of diamond powder was made up as follows: 5 g of average particle size 1.8 micro meters, 16 g of average particle size 3.5 micro meters, 7 g of average particle size 5 micro meters, 44 g of average particle size 10 micro meters and 28 g of average particle size 20 micro meters. This multimodal particle size distribution extended from about 1 micro meter to about 30 micro meters.
  • the diamond powder had been rendered hydrophilic by prior acid cleaning and washing in de-ionised water.
  • an aqueous solution of cobalt nitrate and a separate aqueous solution of sodium carbonate were simultaneously slowly added while the suspension was vigorously stirred.
  • the cobalt nitrate solution was made by dissolving 123.5 grams of cobalt nitrate hexahydrate crystals, Co(NO 3 ) 2 .6H 2 O, in 200 ml of de-ionised water.
  • the sodium carbonate solution is made by dissolving 45 g of pure anhydrous sodium carbonate, Na 2 CO 3 in 200 ml of de-ionised water.
  • the cobalt carbonate precursor compound for cobalt took the form of whisker shaped crystals decorating the diamond particle surfaces identical in form to those shown in FIGS. 9 a and b .
  • the sodium nitrate product of reaction was removed by a few cycles of decantation and washing in de-ionised water.
  • the powder was finally washed in pure ethyl alcohol, removed from the alcohol by decantation and dried under vacuum at 60° C.
  • the dried powder was then placed in an alumina ceramic boat with a loose powder depth of about 5 mm and heated in a flowing stream of argon gas containing 5% hydrogen.
  • the top temperature of the furnace was 700° C. which was maintained for 2 hours before cooling to room temperature.
  • This furnace treatment dissociated and reduced the cobalt carbonate precursor to form pure cobalt particles decorating the surfaces of the diamond particles. In this way it was ensured that the cobalt particles were always smaller than the diamond particles with the cobalt being homogeneously distributed.
  • the conditions of the heat treatment were chosen with reference to the cobalt carbon phase diagram of FIG. 7 . At 700° C. it may be seen that the solid solubility of carbon in cobalt is low.
  • PCD free standing, macro residual stress free, bodies each comprising an intergrown diamond network where the grain size distribution extends from about 2 micro meters to about 30 micro meters, with a mean grain size of close to 10 micro meter together with an inter-penetrating metallic network made up of pure cobalt were manufactured.
  • the overall diamond content was pre-selected independently of the diamond size distribution and metal composition to be about 95 volume % with the metal being a corresponding 5 volume %.
  • the preparation method in this example was changed compared to that of Example 2 with the intention of creating favourable micro structural consequences related to degree of intergrowth and contiguity of the diamond grains.
  • the basis of the change of preparation method was that the precursor compound for the metal component of the PCD was decorated onto a pre-selected portion of the diamond powder.
  • the pre-selected portion upon which all of the metal was decorated was made up of the three coarsest size fractions which also correspond to about half of the total diamond particle surface area.
  • PCD free standing, macro residual stress free, bodies were made with the same diamond composition and size distribution as in Example 2.
  • the metal was pre-selected independently to be 9 volume percent pure Nickel.
  • the method as outlined in FIG. 5 column 2 was used. The following sequential steps and procedures were carried out in order to so manufacture this PCD free standing body, differing from Example 2 in that the precursor compound was a hydroxide as opposed to a carbonate.
  • PCD free standing, macro residual stress free, bodies were made with the same diamond composition and size distribution as in Examples 2 and 4.
  • the metal was pre-selected independently to be 9 volume percent of a iron, 33 weight percent nickel alloy.
  • the method as outlined in FIG. 5 column 2 was used. The following sequential steps and procedures were carried out in order to so manufacture this PCD free standing body.
  • the precursor compound was a mixed ferrous, nickel carbonate.
  • PCD free standing, macro residual stress free, bodies were made with the same diamond composition and size distribution as in Examples 2, 4 and 5.
  • the metallic network was pre-selected independently to be 9 volume percent of the PCD, and to be a cobalt, tungsten carbide cermet.
  • This cermet itself was pre-selected to be made up of 78 volume percent cobalt and 22 volume percent tungsten carbide (66.8 weight percent cobalt, 33.2 weight percent tungsten carbide).
  • PCD free standing bodies each comprising an intergrown diamond network and an interpenetrating metallic network were made using a starting diamond powder with an average particle size of 0.5 micro meters.
  • the metallic network was pre-selected to be 11 volume percent of the PCD material with the metal independently pre-selected to be a 50% by weight nickel, 50% by weight copper alloy.
  • the PCD body was a right cylinder 13 mm in diameter and 8 mm long.
  • the method as outlined in FIG. 5 column 2 was used whereby the precursor for the metallic component of the PCD body was reactively created in a water liquid suspension of starting diamond particles and was caused to nucleate and grow on the surfaces of the starting diamond particles. The following sequential steps and procedures were carried out in order to so manufacture this PCD free standing body.
  • FIG. 14 shows a 3-dimensional shaped PCD body intended for use in general applications.
  • the body was of 45 mm of overall length.
  • These PCD bodies are intended for use in general applications where rock removal is required, such as cutting elements in rotary rock drills or road planing heads.
  • the bodies had a cylindrical barrel of diameter 25 mm diameter and 25 mm long.
  • the cutting end was designed to have a sloping rounded chisel shape.
  • the bodies were of 45 mm of overall length.
  • PCD free standing, macro residual stress free, bodies each comprising an intergrown diamond network with a mean grain size of close to 10 micro meters with an inter-penetrating metallic network made up of cobalt at 9 volume % were manufactured.
  • the PCD bodies were chosen to be large discs with the desired diameter of 100 mm and thickness of 3 mm.
  • a polycrystalline diamond (PCD) construction or body which is free standing in that it is not attached or bonded, in any manner during any stage of the manufacture of the PCD, to a second body or substrate of a dissimilar material.
  • a substrate such as tungsten carbide/cobalt hard metal commonly used in conventional PCD constructions where the cobalt binder metal is infiltrated into a mass of diamond powder to facilitate diamond particle-to-particle sintering is excluded.
  • Manufacturing methods whereby the metals required to enable sintering of the diamond particles are homogeneously combined with a pre-selected diamond powder of chosen specific size distribution are also described. These may allow both the amount and specific metallurgy of the metals to be independently pre-selected and chosen such that they are independent of the chosen diamond size and size distribution. Thus, key manufacturing degrees of freedom such as the diamond grain size distribution, the metal content of the PCD material and the atomic and alloy composition of the metal may be chosen and pre-selected independent of one another.
  • the PCD body so formed may comprises a single volume of PCD material which is homogeneous at a macroscopic scale, i.e., above a scale defined for this invention to be greater than ten times the average diamond grain size, with the coarsest component of grain size being three times the average grain size.
  • the homogeneity at this scale provides for the PCD body to be considered as a spatially invariant material. At this macroscopic scale the PCD body is therefore stress free, having an absence of residual stress.
  • Another consequence of not directionally infiltrating from a substrate is that the PCD body or construction is dimensionally unrestricted in this regard in any or all orthogonal directions. The dimensions in any particular direction are restricted only by the size of the high pressure apparatus used to manufacture the PCD body.
  • the dimensions in any or all of the orthogonal directions may be up to 100 mm or more.
  • the PCD body or construction can thus be viewed as a true 3-dimensional body of any shape and is not restricted to a layer or plate where one dimension is always of the order of a few millimeters, as is the case for conventional PCD bodies or constructs.
  • diamond particles are combined with the metals, alloys or metal/metal carbide combinations for PCD materials such that the metallic particles, grains or entities are smaller than the diamond particles. This may ensure the homogeneity of metal diamond distribution at a scale greater than the diamond particle or subsequent grain size maximum.
  • the metals, alloys or metal/metal carbide in the mass are the sole source of the molten metal necessary and required to cause the sintering of the diamond particles via partial diamond re-crystallization mechanisms.
  • One method to create particulate diamond-metal masses involves the crystallization of the precursor compound or compounds for the desired metallic particles from solution where the diamond powder particles are present in suspension in the solution.
  • the precursor compound may be formed using any of the crystallization procedures known in the art, such as using reduction of temperature and or removal of solvent by evaporation. After total removal of the solvent, liquid suspension media, a well-mixed intimate combination of the diamond powder and precursor compound or compounds for the metal particles is produced.
  • This method uses precursor compounds which are soluble in the liquid suspension media. Examples of liquid media or solvents are water and alcohol. Examples of possible precursor compounds are ionic salts, particularly the nitrates of the transition metals.
  • the precursor compounds are dissociated and reduced to form the metallic particles by a heat treatment preferably in a reducing furnace environment.
  • Another method concerns the chemical reactive generation of the desired precursors for the desired metallic particles in liquid media with the presence of the diamond powders in suspension.
  • Such precursors are significantly insoluble in the suspension media.
  • the precursor compounds may nucleate and grow on the diamond particle surfaces to form a particulate decoration of the diamond surfaces with particles or grains of the precursor compounds.
  • the surface chemistry of the diamond particles may be pre-selected and/or deliberately altered to be hydrophilic and dominated by oxygen species prior to the suspension decoration with the precursor compounds.
  • the precursor compounds are dissociated and reduced by a heat treatment, for example in a reducing furnace environment, to form metallic particles which decorate the diamond particle surfaces and do not form a continuous metallic coat.
  • the furnace environment may be a vacuum or involve flowing gas mixtures containing at least one gas capable of reducing the precursors or its dissociative products to the metallic state and/or metal carbide.
  • Typical reductive gases are hydrogen and carbon monoxide.
  • the heat treatment conditions may be pre-selected to be sufficiently high in temperature and of a sufficiently long duration to cause controlled amounts of amorphous non-diamond carbon to be formed on the metal and diamond surfaces.
  • the heat treatment conditions may be pre-selected to be sufficiently low in temperature and short in time for non-diamond carbon not to form at a detectable level.
  • temperatures above 800° C. for times of an hour or more are typical of the former case.
  • the presence or absence of amorphous non-diamond carbon together with the control of its amount in the diamond/metal particulate mass is a degree of freedom which may play a role in the sintering mechanisms of the diamond particles.
  • the metallic particles now decorate the diamond particle surfaces. This approach may assist in ensuring that the metallic particles are always smaller than the diamond particles.
  • liquid media may include water and alcohols.
  • Some precursors may be insoluble salts of the transition metals such as carbonates, oxalates, acetates, tungstates, tantalates, titanates, molybdates, niobates, and the like.
  • the reactants to reactively form these precursors are soluble salts in the chosen solvent or suspension medium.
  • a reactant source of transition metals such as iron, nickel, cobalt, manganese, chromium, copper and the like may be nitrate salts.
  • precursor compounds for transition metals which form stable carbides such as tungsten, molybdenum, tantalum, titanium, niobium, zirconium and the like may be oxides generated by the reaction of alkoxide compounds with water in alcohol suspension media.
  • a reaction to generate tungstic oxide, WO 3 as a precursor to form tungsten carbide on diamond particle surfaces may be the reaction of ammonium paratungstate with dilute mineral acids such as nitric acid in water as solvent and suspension medium for the diamond.
  • any of these chemical reactions to form the precursor compound decorants on the diamond particle surfaces may be done in sequence and applied to the pre-selected diamond powder as a whole or to any component of the diamond powder in appropriate suspension media.
  • the diamond powder components may be based upon mass fractions or upon size, size distribution or any desired combination of these. Some of the diamond powder components may be left undecorated.
  • Diamond powder fractions or components may also differ in diamond type, based upon the lattice defect composition and structure of the diamond crystals.
  • a convenient way of such differentiation of diamond type between the diamond powder fractions or components can be to use diamond of natural origin as opposed to standard synthetic diamond origin.
  • the lattice defects in natural diamonds are typically and predominantly made up of aggregated nitrogen impurity atomic structures.
  • the lattice defects in typical synthetic diamonds commercially crystallized using molten transition metal solvents are overwhelmingly dominated by single nitrogen atoms which substitute for individual carbon atoms.
  • the overall nitrogen content in natural diamond is typically an order of magnitude greater than for such synthetic diamond.
  • PCD materials made with these different types of diamond exhibit significantly different properties. Pre-selected combinations of natural and synthetic diamonds may also be used for purpose.
  • the precursor compounds are dissociated and reduced to form metallic particles by a heat treatment, for example in a reducing furnace environment.
  • different components of the diamond powder may be decorated in any of the different metallic particles and to any different degree.
  • the metallic particles may be pre-selected both in elemental composition and amount to be associated and decorated onto any chosen sub-component of the diamond particles.
  • a vast number of PCD free standing body embodiments with desired compositions, structures and properties may, in this way, be generated using such prepared decorated diamond powder, metal combinations or masses.
  • the methods involving liquid suspension procedures may have particular utility in that they may be easily altered in scale and may allow production quantities of kilograms or more of accurate, homogeneous combinations of the diamond and metals and metals/metal carbides to be made.
  • a notable and valuable characteristic of one method is that wide ranging combinations of diamond particles and metals, which may be pre-selected to vary independently in diamond particle size, metal amount and metal elemental composition, may be made.
  • the masses of diamond particle, metal combinations generated by the above methods are consolidated into cohesive so called “green bodies” of a pre-selected size and 3-dimensional shape. Consolidation may be effected in compaction die arrangements or isostatic compaction apparatuses as known in the art. Preferably hot isostatic compaction may be employed. Isostatic compaction techniques may have the benefit of spatial homogeneity of density in the green body, which assists in ensuring that the homogeneity of the starting diamond powder, metal combination is maintained and in turn engenders directionally equal shrinkage during subsequent sintering of the diamond particles. Free standing PCD bodies of near net pre-determined shape may then be made. The degree of shrinkage on sintering to form the PCD body may be measured for each specific diamond and metal composition. Such knowledge allows the size of resultant PCD body to be preselected for each PCD composition. Free standing PCD bodies of near net pre-determined size may then be made.
  • Temporary organic binders may be employed to provide cohesion in the green bodies.
  • gel casting techniques may be employed as known in the art.
  • This technique to form the green bodies also maintains spatial homogeneity of the diamond and metal distributions so that directionally equal shrinkage on sintering may occur, so that the 3-dimensional shape of the green body may be maintained on formation of the free standing body.
  • powder, slurry and suspension based consolidation and green body formation techniques known in the art for material fabrication from particulate starting materials. In addition to those already disclosed above, these include injection moulding, slip casting, electrophoresis enhanced sedimentation, centrifugal enhanced sedimentation, 3-dimensional printing and many others.
  • Each of the consolidation and green body making techniques has it own character in regard to the size of particles it may viably be applied to and also the degree to which homogeneity including that of porosity can be maintained.
  • Preferences of techniques to be applied to make any given 3-dimensional and material embodiments take such character of the technique into consideration.
  • the ability of a technique to be accurate, reproducible and maintain spatial homogeneity all in regard to porosity is of importance in the choice of preferred techniques to be used for any particular embodiment. This consideration is directed at the achievement of near net size and shape.
  • the green bodies generated by the above methods are subjected to high pressure, high temperature conditions for appropriate times to cause sintering of the diamond particles and form the free standing PCD bodies.
  • Typical pressure and temperature conditions are in the range of 5 to 15 GPa and in the range of 1200 to 2500° C. respectively.
  • pressures in the range 5.5 to 8.0 GPa along with temperatures in the range 1350 to 2200° C. may be used.
  • a means of managing and controlling the micro residual stress magnitude of the free standing macro residual stress free PCD body i.e., below a scale defined to be less than ten times the average grain size, where the coarsest component of grain size is no greater than three times the average grain size. Above this scale some embodiments provide for the PCD free standing body to be residual stress free, i.e., macro residual stress free.
  • the methods disclosed may allow a very wide range of diamond to metal ratios and accurate metal compositions to be pre-selected independently of resultant diamond grain size and size distribution. Thus the relative differences in thermo-elastic properties between the diamond network and that of the metallic network can be pre-selected and accurately controlled.
  • the dominant properties in this regard are the thermal expansion coefficients of the metals in comparison to that of diamond.
  • the relative differences of properties cause the diamond network to be generally compressed and the metallic network generally put into a state of tension.
  • the micro residual stress magnitudes may thus be considered to be high, medium or low in magnitude by the use of metal compositions with thermal expansion coefficients in the ranges of 10 to 14, 5 to 10 and less than 5 ppm ° K ⁇ 1 , respectively.
  • Some embodiments include the high carbon versions of controlled expansion transition metal alloys.
  • a notable low expansion alloy with a very low minimum of linear coefficient of thermal expansion is an iron, 33 weight % nickel, 0.6 weight % carbon alloy (ref. 4).
  • This alloy has a literature linear coefficient of thermal expansion value of 3.3 ppm ° K ⁇ 1 , which falls into the less than 5 ppm ° K ⁇ 1 category.
  • This alloy would then be expected to provide a metallic network in PCD materials where the tensile residual stress magnitude in the metallic network is low.
  • this alloy has an elastic modulus of approximately 200 GPa, which is very different and removed from the elastic modulus of the diamond network, typically 1050 GPa.
  • the elastic property difference should dominate when the manufacturing conditions are returned to room conditions.
  • the differential expansion of the diamond and metallic networks on release of pressure should then result in the metallic network experiencing a compressive micro residual stress.
  • metals of low thermal expansion coefficients it is possible that the residual stress in the metallic network can become compressive.
  • any or all of the above aspects may provide for the manufacture of free standing PCD bodies, not attached to a dissimilar material, comprising a pre-selected combination of intergrown diamond grains of specific size and size distribution, in conjunction with an independently pre-selected specific metallic inter-penetrating network, with an independently pre-selected specific overall metal to diamond ratio.
  • These primary degrees of freedom may be independently pre-selected.
  • Some embodiments may benefit from removal of the metal from a chosen depth from the surface of the PCD body or throughout the volume of the PCD body. This may be done using, for example, chemical leaching techniques well known in the art.
  • embodiment methods involve, for example, diamond particle suspension in a liquid and the crystallisation and/or precipitation of precursor compound for the required metals of the PCD material to be formed and the subsequent thermal decomposition/reduction of these precursors to form the metals.
  • These methods are inherently characterised by the resultant metallic particles being smaller than the chosen diamond particles.
  • the described methods involving diamond particle suspensions and the crystallisation and/or precipitation of precursor compounds for the metals become more and more practicable and efficient as the diamond particle sizes become smaller and smaller down to and including sub-micron sizes. This is due to the precursor compounds for the metals being influenced in their crystallisation and/or precipitation by the overall diamond surface area, which becomes progressively larger as the diamond particles become smaller.
  • This character of these suspension methods provides for a high degree of homogeneity of mix of the diamond particles and metallic particles, and may even approach the ultimate homogeneity in this regard.
  • This homogeneity of diamond and metal in a particulate mass assists in the formation of a green body and subsequent free standing PCD body formed at high pressure high temperature which is homogeneous with respect to its diamond and metallic composition above a scale related to the average and maximum grain size of the diamond grain size of the diamond network and also which spans the dimensions of the free standing PCD body.
  • This scale can be used to define the so-called “macroscopic” scale of the PCD material.
  • the diamond network to metallic network volume ratio is spatially constant and invariant above a scale greater than ten times the average diamond grain size, provided that the largest component of diamond grain size is no greater than three times the average diamond grain size.
  • This spatial invariance of diamond network to metallic network volume ratio at the defined macroscopic scale, across the dimensional span of the PCD body means that, at completion of the manufacturing process, the free standing PCD body will be macroscopically residual stress free.
  • the PCD material from place to place will differ in thermal expansion and elastic properties. These spatial differences in properties then necessarily lead to a significant macroscopic residual stress field across the dimensional span of the PCD body, caused by the spatial differential in contraction, when the PCD body is returned to room temperature and pressure at the end of the high temperature high pressure process.
  • Free standing PCD bodies of embodiments which are residual stress free may have considerable benefits in applications involving mechanical action such as general machining, drilling and the like.
  • the tooling material efficiency is often governed by crack related processes leading to undesired fracture behaviour such as chipping and spalling.

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CN109706340B (zh) * 2019-01-23 2020-04-28 深圳市海明润超硬材料股份有限公司 一种细粒度金刚石聚晶及其制备方法
CN111974310B (zh) * 2020-09-07 2022-04-01 中国有色桂林矿产地质研究院有限公司 一种基于负载钴催化剂的金刚石微粉制备聚晶金刚石复合片的方法
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