POLYCRYSTALLINE DIAMOND COMPOSITE COMPACT ELEMENT, TOOLS INCORPORATING SAME AND METHOD FOR MAKING SAME

Abstract

The invention relates to a PCD composite compact element comprising a PCD structure integrally bonded at an interface to a cemented carbide substrate; the PCD structure comprising coherently bonded diamond grains having a mean size no greater than 15 microns; the cemented carbide substrate comprising carbide particles dispersed in a metallic binder, the carbide particles comprising a carbide compound of a metal; wherein the ratio of the amount of metallic binder to the amount of the metal at points in the substrate deviates from a mean value by at most 20 percent of the mean value. The invention further relates to a method for making a PDC compact element comprising a PCD structure integrally bonded to a substrate formed of cemented carbide; the method including introducing a source of excess carbon to the substrate at a bonding surface of the substrate to form a carburised substrate; contacting an aggregated mass of diamond grains with the carburised substrate; and sintering the diamond grains in the presence of a solvent/catalyst material for diamond; wherein the mean size of the diamond grains in the aggregated mass is no greater than 30 microns.

Claims

1. A method for making a polycrystalline diamond composite (PDC) compact element comprising a polycrystalline diamond (PCD) structure integrally bonded to a substrate formed of cemented carbide; the method including introducing a source of excess carbon to the substrate at or proximate a bonding surface of the substrate to form a carburised substrate or carburised substrate assembly; contacting an aggregated mass of diamond grains with the carburised substrate or carburised substrate assembly adjacent or proximate the bonding surface to form an unbonded assembly; and sintering the diamond grains in the presence of a solvent/catalyst material for diamond at a temperature and pressure at which diamond is thermodynamically stable to form POD; wherein the mean size of the diamond grains in the aggregated mass is no greater than about 30 microns.

2. A method according to claim 1, including introducing at least 0.1 weight percent source of excess carbon to the substrate at or proximate the bonding surface of the substrate wherein the weight percent is expressed as of the total substrate material within the region in which the carbon is introduced.

3. A method according to claim 1, including forming the aggregated mass from diamond grains having a multi-modal size distribution.

4. A method according to claim 1, wherein the source of excess carbon is in the form of carbon black powder or graphite.

5. A method according to claim 1, including introducing diamond to the substrate at or proximate the bonding surface of the substrate and converting at least some of the diamond into graphite to serve as a source of excess carbon.

6. A method according to claim 1, including combining source of excess carbon in particulate or granular form with raw materials for the cemented carbide, forming the combination into a substantially self-supporting green body, and sintering the green body at a pressure at which diamond is not thermodynamically stable.

7. A method according to claim 1, including combining diamond grains with raw materials for cemented carbide, forming the combination into a substantially self-supporting green body; subjecting the green body to a temperature of at least 500 degrees centigrade and a pressure at which diamond is not thermodynamically stable.

8. A method according to claim 1, including introducing refractory metal carbide particles into the aggregated mass of diamond grains, the refractory metal carbide particles being selected from the group consisting of tungsten carbide, tantalum carbide, niobium carbide and vanadium carbide and/or introducing a refractory metal precursor for metal carbide into the aggregated mass of diamond grains, the refractory metal being selected from the group consisting of tungsten, tantalum, niobium and vanadium in non-carbide compound or in elemental form.

9. A method according to claim 1, wherein the step of introducing the source of excess carbon comprises dispersing the source of excess carbon is throughout the volume of the carburised substrate or carburised substrate assembly.

10. A method according to claim 1, wherein prior to the step of contacting the aggregated mass of diamond grains with the carburised substrate or carburised substrate assembly the method further comprising forming the carburised substrate by sintering a mixture comprising tungsten carbide grains, a binder material and the source of excess carbon.

11. A method according to claim 1, wherein the step of introducing the source of excess carbon comprises introducing no greater than about 10 weight percent of the of the source of excess carbon in the surface region or the substrate.

12. A method according to claim 1, wherein the content of the source of excess carbon within the surface region or throughout the entire carburised substrate is at least about 0.1 weight percent of the surface region or substrate.

13. A method according to claim 1, wherein the content of the source of excess carbon within the surface region or throughout the entire carburised substrate is at least about 0.3 weight percent of the surface region or substrate.

14. A method according to claim 1, wherein the surface region extends to a depth of at least about 1 mm, at least about 2 mm, or even at least 3 mm from the bonding surface.

15. A method according to claim 1, wherein the source of excess carbon is introduced in the form of a gas.

16. A method according to claim 1, comprising combining the source of excess carbon in particulate or granular form with raw materials for the cemented carbide, forming the combination into a substantially self-supporting green body, and sintering the green body at a pressure at which diamond is not thermodynamically stable to form the carburised substrate

Description

DRAWING CAPTIONS

[0066] Non-limiting embodiments will now be described with reference to the accompanying drawings of which:

[0067] FIG. 1 shows (a) a schematic drawing of a perspective view of an embodiment of a PCD composite compact element, as well as longitudinal side cross-sectional views of two embodiments, (b) and (c).

[0068] FIGS. 2 to 7 are schematic drawings of perspective views of embodiments of PCD composite compact elements.

[0069] FIG. 8 shows a graph of number of grains versus equivalent circle diameter grain size for a fine-grained bi-modal size distribution of diamond grains within an embodiment of PCD material.

[0070] FIG. 9 shows a graph of number of grains versus equivalent circle diameter grain size for diamond grains within an embodiment of PCD material.

[0071] FIG. 10 shows a schematic graph of binder content as well as the carbon content in the PCD and the substrate as a function of depth from the PCD working surface in the case of a prior art PCD composite compact as well as in the case of an embodiment of the invention.

[0072] FIG. 11 is a graph showing the ratio of cobalt to tungsten content as a function of distance into the substrate from the interface with the PCD structure, in the case of an embodiment of the invention (data shown as filled squares) and a control according to the prior art (data shown as unfilled diamonds).

[0073] FIG. 12 is a graph showing the ratio of cobalt to carbon content as a function of distance into the PCD structure from the interface with the substrate, in the case of an embodiment of the invention (data shown as filled squares) and a control according to the prior art (data shown as unfilled diamonds).

[0074] FIG. 13 shows a scanning electron micrograph of a cross-section of a bonding interface between a PCD structure and a cobalt-cemented WC substrate enhanced with diamond.

DETAILED DESCRIPTION OF EMBODIMENTS

[0075] With reference to FIG. 1, an embodiment of a polycrystalline diamond composite compact (PCD) element, 100, comprises a PCD structure, 110, integrally bonded to a cemented carbide substrate, 120, at an interface, 125. In some embodiments the interface between the embodiment shown in (a) The PCD structure, 110, has an axial thickness t.sub.PCD and the substrate, 120, has an axial thickness t.sub.sub, the axial thickness being measured from an interface, 125, between the PCD structure, 110, in an axial direction indicated by the line marked “axial”. In an embodiment shown in (b), the interface, 125, is substantially planar, and in an embodiment shown in (c), the interface, 125, is non-planar and the PCD structure, 110, has at least two thicknesses, t.sub.PCD-1 and t.sub.PCD-2.

[0076] With reference to FIG. 2, an embodiment of a polycrystalline diamond composite compact (PCD) element, 100, comprises a PCD structure, 110, integrally bonded to a cemented carbide substrate, 120, at an interface, 125, and the PCD structure comprises a first region, 112, and a second region, 111, the mean size of the diamond grains of the first region, 112, being greater than that of the diamond grains in the second region, 111; the first region, 112, being proximate the substrate, 120, and the second region, 111, being remote from the substrate, 120.

[0077] With reference to FIG. 3, an embodiment of a polycrystalline diamond composite compact (PCD) element, 100, comprises a PCD structure, 110, integrally bonded to a cemented carbide substrate, 120, at an interface, 125, wherein the substrate, 120, includes diamond particles dispersed within a surface region, 221, extending from the interface to a depth. The remaining region, 122, of the substrate, 120, is substantially free of diamond. In some embodiments the depth is at least 1 millimetre, at least 2 millimetres or at least 3 millimetres. In some embodiments the surface region, 121, of the substrate has a volume of at least 2 times that of the PCD structure, 110, at least 3 times that of the PCD structure, 110, or even at least ten times greater than the volume of the PCD structure, 110.

[0078] With reference to FIG. 4, an embodiment of the method of the invention includes introducing a source of excess carbon to the substrate, 220, at or proximate a bonding surface, 225, to form a carburised substrate assembly, 250; contacting an aggregated mass, 210, of diamond grains with the carburised substrate assembly, 250, adjacent or proximate the bonding surface, 225, to form an unbonded assembly, 200; wherein the source of excess carbon is in the form of graphite dispersed in a surface region, 221, of the substrate, 220, the surface region extending from proximate the bonding surface, 125, to a depth. In some embodiments the depth is at least 1 millimetre, at least 2 millimetres or at least 3 millimetres. With reference to FIG. 5, the source of excess carbon is in the form of graphite dispersed substantially throughout the entire volume of the substrate, 220.

[0079] With reference to FIG. 6, an embodiment of the method of the invention includes introducing a source of excess carbon to the substrate, 220, at or proximate a bonding surface, 225, to form a carburised substrate assembly, 250; contacting an aggregated mass, 210, of diamond grains with the carburised substrate assembly, 250, adjacent or proximate the bonding surface, 225, to form an unbonded assembly, 200; wherein the source of excess carbon, 230, is deposited onto a bonding surface, 125, of the substrate. With reference to FIG. 7, an embodiment of the method of the invention includes placing a disc or film, 240, comprising tungsten over the deposited source of excess carbon, 230.

[0080] For example, FIG. 8 shows a graph of number of grains versus equivalent circle diameter grain size for a fine-grained bi-modal size distribution of diamond grains within an embodiment of PCD material; and FIG. 9 shows a graph of number of grains versus equivalent circle diameter grain size for diamond grains within an embodiment of a multi-modal PCD material.

[0081] The PCD material having the diamond grain size distribution shown in FIG. 8 is an example of an embodiment of PCD material that may benefit particularly well from the invention, wherein the mean size of the diamond grains within the sintered PCD is in the range from about 1.5 to about 6 microns and the size distribution can be resolved into at least two distinct peaks. FIG. 8 shows the distribution of equivalent circle diameters, with no Saltykov correction having been applied to convert the size distribution obtained from the two-dimensional image data to a grain size distribution in three dimensions.

[0082] With reference to FIG. 9, the relative (e.g. weight percent) content of cobalt, 200, within a prior art PCD composite compact, 210, and a PCD composite compact according to an embodiment of the invention, 220, are compared in respect of qualitative features. In some embodiments of the invention binder pooling is substantially reduced. In some embodiments the incidence of plume defects is substantially reduced. Also shown in FIG. 9 are the corresponding relative content of carbon, 400, within a prior art PCD composite compact, 410, and a PCD composite compact according to an embodiment of the invention, 420, are compared in respect of qualitative features. The region of the graphs indicated by 110 corresponds to the PCD structure and the region indicated by 121 corresponds to the carbide substrate.

[0083] FIG. 10 is a graph showing the ratio of cobalt to tungsten as a function of axial distance into the substrate from the interface with the PCD structure, in the case of an embodiment of the invention (data shown as filled squares) and a control according to the prior art (data shown as unfilled diamonds). The interface corresponds to zero millimetres. In an embodiment of the invention, the ratio (shown as filled squares) remains substantially constant from the interface into the bulk of the substrate, the standard deviation of the data being less than about 5 percent of the mean value, M. The upper and lower standard deviations are indicated as SU and SL, respectively. The upper and lower percent limits or M(1+20%) and M(1−20%), are shown as LU and LL, respectively. In the case of a control material, made according to the prior art, the mean ratio of cobalt to tungsten is substantially lower within a depth of approximately 1.5 millimetres is substantially and systematically less than the mean value in the bulk of the substrate, and is less than the lower limit M(1−20%) within a depth of about 1 millimetre from the interface. This is called the “depleted zone”.

[0084] FIG. 11 is a graph showing the ratio of cobalt to carbon as a function of axial distance into the PCD structure from the interface with the substrate, in the case of an embodiment of the invention (data shown as filled squares) and a control according to the prior art (data shown as unfilled diamonds). The interface corresponds to zero millimetres. In an embodiment of the invention, the ratio (shown as filled squares) remains substantially constant from the interface into the bulk of the PCD structure, even within the first 0.2 millimetres from the interface, where the ratio in the control material increases dramatically to greater than M(1+20%), corresponding to binder pooling within the PCD structure adjacent the interface.

[0085] With reference to FIG. 12, an SEM micrograph of the region straddling an interface between a PCD structure, 40, and a cemented carbide substrate, 50, of a PCD composite compact according to an embodiment of the invention is shown. The substrate, 50, contains particles of diamond, 46. A “finger”, 45, comprising contiguous polycrystalline diamond and having a length in the range of about 30 to 50 microns extends from the PCD structure, 40, into the substrate, 50.

[0086] As previously noted, embodiments of the invention may comprise relatively thick PCD caps and substrates without the need for using higher temperatures in the sintering step. In general, the thicker the PCD layer, the higher must be the sintering temperature in order to urge molten solvent/catalyst material from the substrate to infiltrate the entire PCD layer. A serious consequence of this not occurring is the presence of “soft spot” defects wherein the diamond grains remote from the interface have not adequately sintered. Unfortunately, higher sintering temperatures result in excessive dissolution of diamond proximate the interface and may result in plume defects in the form of exaggerated large acicular metal carbide grains. On the other hand, higher sintering temperatures tend to promote exaggerated diamond grain growth, which is also undesirable. This is less of a problem where the PCD structure is relatively thin, since the minimum sintering temperature for the avoidance of soft spots is lower the thinner the PCD structure. However, many applications require that the PCD structure is several millimetres thick and that the substrate is tens of millimetres thick. In particular, PCD compacts used for boring into earth and rock in the oil and gas industry comprise relatively thick PCD caps and substrates.

[0087] The invention will now be described with reference to the following non-limiting examples.

Example 1

[0088] A first substrate element for use as the surface region of a substrate for a PCD compact was manufactured by blending together diamond particles, tungsten carbide (WC) powder and cobalt powder, forming the blended mixture into a compacted green body, and subjecting the green body to a conventional carbide sintering process. The diamond particles had mean size in the range of 0.75 to 1.5 microns, and constituted 3 weight percent of the blended mixture. The WC powder and the cobalt powder had been pre-mixed, the cobalt constituting 13 weight percent of the WC-Co pre-mix and the WC particles having a mean size in the range from about 1 to 4 microns. About 2 weight percent organic pressing aid was included in the WC-Co mix. The blended powder mix was uniaxially compacted at ambient temperature to form a substantially cylindrical green body, which was conventionally sintered at a temperature of 1,400 degrees centigrade for 2 hours to form a sintered article. By the end of the sintering process, the diamond particles had completely converted into graphite. The substrate had a diameter of about 17.4 millimetres and a height of about 6 millimetres after final machining.

[0089] A second substrate element for use as a region of a substrate substantially free of diamond was manufactured in the same way and using the same raw materials as the first substrate element, except that no diamond was introduced and the height of the second substrate element was about 7 millimetres.

[0090] The first substrate element was placed on top of the second substrate element, the first and second substrate elements being substantially in registration, to form a substrate assembly, having an upper surface being the exposed end surface of the first substrate element.

[0091] A layer comprising an unbonded aggregated mass of diamond grains was deposited onto the upper surface of the substrate assembly end surface of the sintered article to form an unbonded assembly. The diamond grains had mean size of about 0.5 microns and were coated with cobalt, which constituted 5 weight percent of the aggregated mass. The coated grains were then subjected to heat treatment in a hydrogen rich atmosphere at 850 degrees centigrade in order to terminate the surfaces with hydrogen.

[0092] The unbonded assembly was mounted within a capsule for an ultra-high pressure furnace, as is known in the art. The capsule was subjected to a pressure of about 5.5 GPa and a temperature of about 1,400 degrees centigrade for a period of about 5 minutes. After sintering, the first and second substrate elements had sintered together and the PCD composite compact was processed in the usual way to form an insert having a diameter of about 15.9 milimetres and a PCD structure with thickness in the range of about 1.7 to 2.1 millimetres.

[0093] The insert was analysed using scanning electron micrography (SEM). Particularly noteworthy was the absence of discernable “pooling” of cobalt binder adjacent the interface between the PCD and the substrate, which is a typical feature of known inserts, especially those having relatively thick PCD and substrate, of which the insert was an example. The sample displayed an abrupt transition between the cemented carbide of the substrate and the PCD. In addition, no substantial exaggerated diamond or WC grains were observed within the PCD layer proximate the interface, as occur in known inserts.

Example 2

[0094] A substrate a PCD compact was manufactured by blending together diamond particles, tungsten carbide (WC) powder and cobalt powder, forming the blended mixture into a compacted green body, and subjecting the green body to a conventional carbide sintering process. The diamond particles had mean size of about 22 microns and constituted about 5.8 weight percent of the blended mixture. The WC powder and the cobalt powder had been pre-mixed, the cobalt constituting 13 weight percent of the WC-Co pre-mix and the WC particles having a mean size in the range from about 1 to 4 microns. About 2 weight percent organic pressing aid was included in the WC-Co mix. The blended powder mix was uniaxially compacted at ambient temperature to form a substantially cylindrical green body, which was conventionally sintered at a temperature of 1,400 degrees centigrade for 2 hours to form a sintered article. By the end of the sintering process, the diamond particles had completely converted into graphite. The substrate had a diameter of about 17.4 millimetres and a height of about 13 millimetres after final machining.

[0095] A layer comprising an unbonded aggregated mass of diamond grains was deposited onto the upper surface of the substrate of the sintered article to form an unbonded assembly. Raw material diamond powder for the aggregated mass was prepared by blending diamond grains from three sources, each source having a different average grain size distribution.

[0096] The unbonded assembly was mounted within a capsule for an ultra-high pressure furnace, as is known in the art. The capsule was subjected to a pressure of about 5.5 GPa and a temperature of about 1,400 degrees centigrade for a period of about 5 minutes. After sintering, the first and second substrate elements had sintered together and the PCD composite compact element was processed in the usual way to form an insert having a diameter of about 15.9 milimetres and a PCD structure with thickness in the range of about 1.7 to 2.1 millimetres.

[0097] The insert was analysed using scanning electron micrography (SEM). The Analysis of the material was carried out at several points on a polished cross-section longitudinally through the interface between the PCD structure and the substrate. The contents of tungsten (W) and cobalt (Co) were measured within the substrate at several different points from proximate the interface into the bulk of the substrate, and the contents of carbon (C) and cobalt (Co) were measured within the PCD structure at several different points from proximate the interface into the bulk of the PCD structure. The results of these measurements are shown as ratios as functions of distance from the interface in FIGS. 11 and 12, respectively. Particularly noteworthy was the absence of substantial “pooling” of cobalt binder adjacent the interface between the PCD and the substrate, which is a typical feature of known inserts, especially those having relatively thick PCD and substrate. The sample displayed an abrupt compositional transition between the cemented carbide of the substrate and the PCD. In addition, substantially no exaggerated diamond or WC grains were observed within the PCD layer proximate the interface, as occur in known inserts.

Example 3

[0098] A substrate a PCD compact was manufactured as in example 2, except that the diamond particles had mean size of about 2 microns and constituted about 2.7 weight percent of the blended mixture. A layer comprising an unbonded aggregated mass of diamond grains as described in example 2 was deposited onto the upper surface of the substrate of the sintered article to form an unbonded assembly, which was sintered as in example 2 to form a PCD composite compact element.

[0099] As in example 2, the absence of substantial “pooling” of cobalt binder adjacent the interface between the PCD and the substrate was observed, and substantially no exaggerated diamond or WC grains were observed within the PCD layer proximate the interface.

Example 4

[0100] A substrate for a PCD compact was manufactured in the same way and using the same raw materials as the first substrate element of example 1, except that the height of the substrate was 13 millimetres. In other words, the whole substrate had substantially the same composition, shape and diameter as the first substrate element described in example 1.

[0101] A layer of unbonded aggregated mass of diamond grains was deposited onto an end surface of the substrate to form an unbonded assembly. The diamond grains had an ultra-fine bi-modal distribution, having a mean size in the range from about 0.1 to 1 micrometre and were coated with cobalt, which constituted 5 weight percent of the aggregated mass. The coated grains were then subjected to heat treatment in a hydrogen rich atmosphere at 850 degrees centigrade in order to terminate the surfaces with hydrogen.

[0102] The unbonded assembly was mounted within a capsule for an ultra-high pressure furnace, as is known in the art. The capsule was subjected to a pressure of about 5.5 GPa and a temperature of about 1,400 degrees centigrade for a period of about 5 minutes. After sintering, the PCD composite compact was processed in the usual way to form an insert having a diameter of about 15.9 milimetres and a PCD structure with thickness in the range of about 1.7 to 2.1 millimetres.

[0103] The insert was analysed using scanning electron micrography (SEM). Particularly noteworthy was the absence of discernable pooling of cobalt binder adjacent the interface between the PCD and the substrate. The sample displayed an abrupt transition between the cemented carbide of the substrate and the PCD. In addition, no substantial exaggerated diamond or WC grains were observed within the PCD layer proximate the interface, as occur in known inserts.

Example 5

[0104] A substrate for a PCD compact was manufactured in the same way and using the same raw materials as the first substrate element of example 1, except that the height of the substrate was 13 millimetres. In other words, the whole substrate had substantially the same composition, shape and diameter as the first substrate element described in example 1.

[0105] A first diamond layer formed of an unbonded aggregated mass of diamond grains was deposited onto an end surface of the substrate, and a second diamond layer formed of an unbonded aggregated mass of diamond grains was deposited onto the first layer to form an unbonded assembly. The first diamond layer had a mean thickness of about 0.5 millimetres and the second diamond layer had a mean thickness of about 2.5 millimetres, the first diamond layer being sandwiched between the substrate and the second diamond layer. The diamond grains of the first diamond layer had a fine-grain bi-modal distribution and the diamond grains of the second diamond layer had an ultra-fine-grain distribution. The diamond grains of the second diamond layer had been coated with cobalt, which constituted 5 weight percent of the aggregated mass, and had then been subjected to heat treatment in a hydrogen rich atmosphere at 850 degrees centigrade in order to terminate the surfaces with hydrogen.

[0106] The unbonded assembly was mounted within a capsule for an ultra-high pressure furnace, as is known in the art. The capsule was subjected to a pressure of about 5.5 GPa and a temperature of about 1,400 degrees centigrade for a period of about 5 minutes. After sintering, the PCD composite compact was processed in the usual way to form an insert having a diameter of about 15.9 milimetres and a PCD structure with thickness in the range of about 2.2 millimetres.

[0107] The insert was analysed using scanning electron micrography (SEM). Particularly noteworthy was the absence of discernable pooling of cobalt binder adjacent the interface between the PCD and the substrate. The sample displayed an abrupt transition between the cemented carbide of the substrate and the PCD. In addition, no substantial exaggerated diamond or WC grains were observed within the PCD layer proximate the interface, as occur in known inserts.

Example 6

[0108] As example 2, except that the capsule was subjected to a pressure of about 6.8 GPa and a temperature of about 1,500 degrees centigrade for a period of about 5 minutes.

[0109] Although the foregoing description of consolidated superhard materials, production methods, and various applications of them contain many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some exemplary embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims are to be embraced.