BRAZED THERMALLY-STABLE POLYCRYSTALLINE DIAMOND COMPACT WORKPIECES AND THEIR FABRICATION

Abstract: Disclosed is a brazed implement comprising a thermally-stable polycrystalline diamond compact, e.g. a compact of self-bonded diamond particles having a network of inter-connected empty pores dispersed throughout the compact, bonded to another of said compact or bonded to a cemented carbide support by a brazing filler metal disposed therebetween. The brazing metal comprises an alloy having a liquidus above about 700°C and containing an effective amount of chromium. Translational shear strengths exceed about 50 kpsi even upon furnace cycling of the brazed implements and often exceed 90 kpsi. The method for fabricating the brazed implement also is disclosed.

Description: The present invention relates to a method for fabricating a brazed implement according to the preamble of claim 1 and a brazed implement according to the preamble of claim 11 (see GB-A-2 163 144). Well known in the super abrasive art are compacts of polycrystalline abrasive particles typified by polycrystalline diamond and polycrystalline cubic boron nitride (CBN) compacts. Such compacts are represented by U.S-A-3,745,623 and 3,608,818 with respect to polycrystalline diamond compacts and U.S-A-3,767,371 and 3,743,489 with respect to polycrystalline CBN compacts. While such polycrystalline compacts represent a significant contribution to the art in many fields of use, thermal degradation at an elevated temperature, e.g. above about 700°C, did limit their usefulness, especially in metal matrix bond applications. Thermal stability of such polycrystalline compacts was improved with the advent of thermally-stable porous self-bonded diamond and CBN compacts containing less than about 3 percent non-diamond phase, hereinafter termed "porous compacts". Compacts of this type are the subject of U.S.-A-4,224,380 and 4,288,248. European Patent Publication No. 116,403 describes a thermally-stable diamond compact comprising a mass of diamond particles present in an amount of 80 to 90% by volume of the body and a second phase present in an amount of 10 to 20% by volume of the body, the mass of diamond particles contain substantially diamond-to-diamond bonding to form a coherent skeletal mass and the second phase containing nickel and silicon, the nickel being in the form of nickel and/or nickel silicide and the silicon being in the form of silicon, silicon carbide, and/or nickel silicide. British patent application GB-A-2 158 086 describes a thermally stable diamond compact comprising a mass of diamond particles present in an amount of 80 to 90% by volume of the compact and a second phase present in an amount of 10 to 20% by volume of the insert, the mass of diamond particles containing substantially diamond-to-diamond bonding to form a coherent skeletal mass and a second phase consisting essentially of silicon, the silicon being in the form of silicon and/or silicon carbide. Diamond, synthetic or natural, is very difficult to wet, making the attachment of diamond to a variety of substrates difficult. Since porous compacts essentially are composed only of diamond, they are difficult to bond to cemented carbide supports, for example. In order to successfully bond porous compacts to cemented carbide supports, a bonding agent that is able to wet and/or adhere to both the diamond surface and the support is required. The bond between the diamond and carbide support must be sufficiently strong so as to provide a useful implement. Temperature conditions required to form the bond must be below those that cause graphitization of the diamond and/or damage to the carbide support system. The bonding agent also must be chemically and physically compatible during and after the bonding operation with both the porous diamond compact and carbide support. The formation of a bond between porous compacts and carbide supports is inhibited by gaseous/liquid/solid films. The inhibiting films can be non-carbon material as well as adsorbed species including water vapor or oxygen. The inhibiting films, by preventing the wetting of the compact and/or carbide support by the bonding agent, reduces the strength of adhesion. Further, blocking of pores in the porous compact by impurities prevents penetration of the bonding agent into the core and reduces the ultimate bond strength. A wide variety of bonding agents, or brazing alloys, have been proposed in the art. With respect to thermally stable diamond compacts, GB-A-2,163,144 recognizes the difficulties encountered in brazing such compacts and, thus, proposes to bond a variety of thermally stable diamond compacts to carbide supports utilizing a silver or gold-based alloy containing at least 40 percent by weight of gold and/or silver and between about 1 and 10 percent by weight of an active metal selected from the group of tungsten, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, and molybdenum. The alloy has a liquidus above 700° C. Data, however, only is given for diamond compacts containing a second phase of silicon, nickel, or their carbides. When the present inventors utilized brazing alloys containing carbide-forming active metals as proposed in this British patent, but when bonding porous compacts (as defined herein), bonding was erratic. Moreover, relatively low bond strengths were realized even when bonding did occur. U.S-A-3,894,673 and 4,018,576 propose to bond single crystals of diamond to metal using nickel/chromium or cobalt/chromium braze alloys. There exists a need in the art for bonding thermally-stable diamond compacts to themselves and to carbide substrates with a bonding agent which provides good bond strength. Moreover, there exists a need in the art to be able to reliably reproduce such bonding. The present invention is addressed to such need in the art. Accordingly, the present invention is directed to a method for fabricating a brazed implement comprised of a thermally-stable compact which comprises self-bonded diamond particles having a network of interconnected empty pores dispersed throughout the compact bonded to another compact or to a cemented carbide support by a brazing filler metal, which method comprises brazing said thermally-stable compact to another thermally-stable compact or to a cemented carbide support using a brazing alloy having a liquidus above 700° C and containing 0 to 35% by weight of gold and/or silver and 1 to 20% by weight of chromium. For present purposes, polycrystalline diamond compacts are termed "thermally stable" by being able to withstand a temperature of 1200° C in a vacuum without any significant structural degradation of the compact occurring. Such polycrystalline diamond compacts are comprised of a polycrystalline mass of diamond particles present in an amount of at least 70% by volume. Another aspect of the present invention is a brazed implement comprising a thermally-stable compact which comprises self-bonded diamond particles having a network of interconnected empty pores dispersed throughout the compact bonded to another of said compact or to a cemented carbide support by a brazing filler metal disposed therebetween which brazing metal is an alloy having a liquidus above 700° C and containing 0 to 35% by weight of gold and/or silver and 1 to 20% by weight of chromium. Advantages of the present invention include the ability to effectively bond thermally-stable polycrystalline diamond compacts to themselves and to cemented carbide supports. Another advantage is the ability to reliably reproduce such bonding. Yet another advantage is the ability to fabricate porous compact/cemented carbide support composites having a transitional shear strength reproducably in excess of 344.5 MPa (50 kpsi). A variety of metals which are carbide formers have been used in braze alloy compositions in order to braze porous polycrystalline diamond compacts to cemented carbide supports. These carbide formers include, for example, chromium, manganese, titanium, cobalt, and tantalum. As the examples will demonstrate, only chromium has been successful in providing reproduceable bonding results. Moreover, only braze alloy compositions containing chromium have been able to provide translational shear strengths which consistently exceed 344.5 MPa (50,000 psi) and which advantageously can exceed 620.1 MPa (90,000 psi). It is believed that even higher bond strengths are possible when the system parameters and braze alloy composition have been optimized. These remarkable results for bonding thermally stable diamond compacts to carbide substrates cannot be predicted or expected based on the single crystal diamond/metal brazing reported above. While the proportion of chromium should be effective for bonding of the porous compacts, the proportion of chromium will range from 1-20 percent and advantageously will be between 5 and 20 percent by weight of the braze alloy composition. The remaining ingredients used are conventional in the braze alloy art. These additional metals control the liquidus of the braze alloy composition which desirably should exceed 700° C, though should be less than 1200° C at which temperature thermal degradation of the thermally-stable compact can commence. Representative metals for inclusion in the braze alloy composition include, for example, nickel, gold, boron, palladium, silver, copper, and the like. It is even possible to utilize other carbide formers in the braze alloy composition, though other carbide formers tested to date do not provide the bonding results which have been achieved with chromium-based alloy compositions. Since neither gold nor silver is responsible for good bonding as taught in GB-A-2,163,144, the high (40% or more) content of these metals is unnecessary, and their presence is limited to 0-35% by weight, i.e. much less than 40%. An alloy composition determined to be quite effective is disclosed in U.S.-A-4,396,577 and an alloy composition thereunder is reported in the Examples. Referring to the porous polycrystalline diamond compacts, reference again is made to U.S-A-4,224,380 and 4,288,248 which provide a full disclosure thereof. The porous polycrystalline diamond compact comprises diamond particles which comprise between 70% and 95% by volume of the compact. The metallic phase of sintering aid material is present substantially uniformly throughout the compact end is in a minor amount, typically ranging from 0.05 to 3% by volume of the compact. A network of interconnected empty pores are dispersed through the compact and are defined by the diamond particles and the metallic phase. Such pores generally comprise between 5% and 30% by volume of the compact. The porous compact is comprised of self-bonded diamond particles typically ranging in size from between about 1 and 1,000 micrometers. The other two types of thermally-stable polycrystalline compacts reported in the art wherein silicon or silicon/nickel essentially replace the empty pore structure of porous polycrystalline diamond compacts are described in the citations referenced above. The cemented carbide support advantageously is comprised of a material selected from the group consisting of cemented tungsten carbide, titanium carbide, tungsten-molybdenum carbide, and tantalum carbide, wherein the metal bond material for the carbide is selected from the group consisting of cobalt, nickel, iron, and mixtures thereof, an elemental metal which forms a stable nitride or boride, and a metal alloy which forms a stable nitride or boride. Cobalt is the bond material of choice in the art as is use of cobalt-cemented tungsten carbide supports. In practicing the present invention, the thermally-stable compact can be bonded to itself or to a carbide support by disposing the chromium-containing braze alloy therebetween and placing such composite in a furnace, for example, to furnace braze the thermally-stable compact. Alternatively, the components can be placed in a press, similar to that wherein conventional polycrystalline compacts are made, and heated to a temperature sufficient for achieving bonding. Preferably, however, bonding is achieved in accordance with the disclosure of EP-A-329 955, which has the same filing date as the present application. Such fabrication technique and apparatus proposes to heat sink the carbide support during the brazing operation while heating through the thermally-stable polycrystalline diamond compact. In this way, residual stresses which otherwise would result by virtue of the mismatch in coefficient of thermal expansion between the carbide and thermally-stable compact can be avoided. This technique also takes advantage of the good thermal conductivity properties of the thermally-stable polycrystalline diamond compact. In addition or alternative to the use of a disk or foil of the chromium braze alloy, the thermally-stable compact can be coated with chromium-containing material which may be the complete braze alloy or may be a portion of the braze alloy with an additional alloy composition in the form of a disk or foil being used during the bonding process. The coating, need only be on the surface of the thermally-stable compact which is to be mated with a surface of another thermally-stable compact or a surface of a cemented carbide support. Alternatively, the entire thermally-stable compact can be coated with the chromium material. Such coating need not be continuous and thick, which provides enhanced oxidation resistance to a porous compact, but need only be present in a sufficient amount so that the bonding proceeds as desired. It will be appreciated that multiple layers of coatings can be used as is necessary, desirable, or convenient. Chromium coatings may be applied to the porous polycrystalline diamond compact by a variety of techniques including, for example, electrolytic plating, metal evaporation, sputtering including reactive sputtering techniques, chemical vapor deposition, pack diffusion, plasma coating, or the like. Certain advantages and limitations are inherent in each of the techniques, e.g. coating thickness and uniformity of thickness, condition of operation, etc. The presently preferred process involves chemical vapor deposition (CVD) of the chromium coating material as this process appears to provide rather uniform thickness and integrity of the resulting coatings. As noted above, an additional braze alloy, with or without chromium, can be placed between the chromium-coated thermally-stable compact and the support or other compact to which it is being bonded, or the coating may be the entire braze alloy composition necessary for achieving the requisite degree of bonding desired. The following examples show how the present invention has been practiced, but should not be construed as limiting. In this application, all citations are expressly incorporated herein by reference. EXAMPLES EXAMPLE 1 Porous polycrystalline cylindrical diamond compacts (1.524 mm (0.060 inch) thick, 1.524 mm (0.060 inch) diameter) were bonded to cylindrical carbide supports (Carboloy® grade 55B carbide; 84% WC, 16% C; 0.762 mm (0.0300 inch) thick, 13.43 mm (0.529 inch) diameter; General Electric Company, Detroit, Michigan, Carboloy being their registered trademark) using the bonding apparatus and process set forth in EP-A-329 955 using a braze alloy having the following composition (wt-%): Ni 58.64 ± 0.7% Pd 30.04 ± 0.1% Cr 8.26 ± 0.75 B Balance This braze alloy is covered in U.S.-A-4,414,178. The recovered brazed supported compacts then were subjected to translational shear strength measurements with the following results being recorded. Sample No. Temperature Profile Shear Strength (kpsi) MPa Heating Cooling 185 Slow Fast (66.4) 457.49 186 Slow Fast (56.8) 391.35 187 Slow Fast (50.0) 344.50 188 Slow Fast (52.1) 358.97 189 Medium Fast (75.8) 522.26 190 Medium Fast (62.5) 430.62 191 Medium Fast (83.8) 577.38 192 Medium Fast (54.3) 374.13 193 Medium Slow (83.3) 573.94 194 Medium Slow (63.4) 436.82 195 Medium Slow (53.4) 367.92 196 Medium Slow ( > 90.0) > 620.10 197 Fast Fast (76.0) 523.64 198 Fast Fast (62.5) 430.62 199 Fast Fast (86.8) 598.05 200 Fast Fast (63.8) 439.58 The mean value of shear strength is 465.76 MPa (67.6 kpsi) with a standard deviation of 91.64 MPa (13.3 kpsi). Again, excellent bond strengths are evident. Based on the foregoing data, the medium ramp up for heating with fast cool down after the braze end point has been reached appeared to provide improved bonding. Thus, addition samples were prepared using this schedule. Sample No. Temperature Profile Shear Strength (kpsi) MPa Heating Cooling 213 Medium Fast (77.7) 535.35 214 Medium Fast (77.3) 532.59 215 Medium Fast (76.4) 526.39 216 Medium Fast (69.9) 481.61 The mean value is 518.13 MPa (75.2 kpsi) with a standard deviation of 26.87 MPa (3.9 kpsi). It should be noted that the same shear fixture was used for all four parts and it was worn afterwards. Lower shear values result from use of a worn fixture. Therefore, the 26.87 MPa (3.9 kpsi) standard deviation probably is high. It should be noted that the displacement endpoint technique was used to determine when bonding was complete. Finally, furnace heating to simulate furnace brazing temperature conditions was conducted by heating two samples under hydrogen to 700° C for one hour, holding this temperature for 15 minutes, and then furnace cooling. Sample No. Furnace Heated Shear Strength (kpsi) MPa 217 Yes (60.3) 415.47 218 Yes (58.6) 403.75 219 No (81.1) 558.78 220 No ( > 86.8) > 598.05 The mean for the non-furnace heated samples was 576.00 MPa (83.6 kpsi) while the mean for the furnace heated samples was 409.95 MPa (59.5 kpsi). Even with the heat treatment supplied, shear strength values above 344.50 MPa (50 kpsi) were achieved. Optimization of brazing conditions should improve performance. EXAMPLE 2 In order to establish the uniqueness of chromium in achieved good brazing of non-porous diamond compacts to carbide supports, several commercial braze alloy compositions were evaluated. These data show that the presence of manganese, cobalt, titanium, and tantalum either does not result in bonding porous compacts to carbide or results in shear strengths generally not exceeding 241.15 MPa (35 kpsi). Use of chromium, however, results in good bonding of porous compacts to carbide and shear strengths generally exceeding 344.50 MPa (50 kpsi) in early testing and exceeding 413.40 MPa (60 kpsi) in later testing. Though sheer strength data is not available, it should be noted that the A85 alloy has been used successfully in bonding porous diamond compacts to porous diamond compacts. EXAMPLE 3 The duration of heating best is controlled by monitoring the longitudinal displacement or stroke of the compact/braze/support configuration. In this example, the displacement past maximum and past minimum was varied and the resulting shear strength of the brazed implement measured. The A-85 alloy of Example 2 was used to braze porous polycrystalline diamond compacts 13.335 mm (0.525 inch) diameter and 1.524 mm (0.060 inch) thick) to carbide supports (Carboloy® grade 55B carbide, 13.436 mm (0.529 inch) diameter, 7.62 mm (0.300 inch) thick). Sample No. End Point d₁ (inch) mm Shear Strength (kpsi) MPa 278 0 (20.4) 140.55 280 0 (41.7) 287.31 289 (0.00005) 1.27x10⁻³ (13.9) 95.77 276 (0.0001) 2.54x10⁻³ (78.5) 540.86 277 (0.0001) 2.54x10⁻³ (66.8) 460.25 279 (0.0001) 2.54x10⁻³ (78.1) 538.11 281 (0.0002) 5.08x10⁻³ (73.8) 508.48 283 (0.0002) 5.08x10⁻³ (73.3) 505.04 284 (0.0003) 7.62x10⁻³ ( > 86.8) > 598.05 291 (0.0003) 7.62x10⁻³ (83.8) 577.38 285 (0.00035) 8.89x10⁻³ ( > 86.8) > 598.05 282 (0.0004) 1.016x10⁻² ( > 86.8) > 598.05 297 (0.0004) 1.016x10⁻² (86.4) 595.29 288 (0.0005) 1.27x10⁻² ( > 86.8) > 598.05 286 (0.00055) 1.397x10⁻² ( > 86.8) > 598.05 292 (0.00065) 1.651x10⁻² ( > 86.8) > 598.05 295 (0.00065) 1.651x10⁻² ( > 86.8) > 598.05 290 (0.00075) 1.905x10⁻² ( > 86.8) > 598.05 296 (0.00080) 2.032x10⁻² ( > 86.8) > 598.05 293 (0.00085) 2.159x10⁻² ( > 86.8) > 598.05 294 (0.00095) 2.413x10⁻² ( > 86.8) > 598.05 Additionally, sample 217 and 218 were subjected to furnace heating to 700°C over a one hour time period, held at 700°C for 15 minutes, and then cooled to room temperature over a 45 minute time period. These samples were subjected to only 344.50 MPa (50 kpsi)shear testing and evidenced no sign of bond failure. With respect to the choice of cemented carbide grade, samples 395, 398, and 401 utilized cemented carbide grade 44A (Carboloy grade 44A cemented carbide; 94% tungsten carbide WC, 6% CO; 13.436 mm (0.529 inch) by 4.468 mm (0.183 inch) thick). Porous polycrystalline diamond compacts 13.335 mm (0.525 inch)by 1.524 mm (0.060 inch) thick) were bonded with the A-85 alloy as described above. All samples proof-tested to 344.50 MPa (50 kpsi) with no evidence of bond failure. Finally, samples Nos. 397, 400, 403, and 404 utilized type 303 stainless steel supports (13.436 mm (0.529 inch) by 4.648 mm (0.183 inch) thick) for bonding porous polycrystalline diamond compacts (13.335 mm (0.525 inch) by 1.524 mm (0.060 inch) thick) using the braze alloy composition of Example 1. Delamination of the samples occurred; however, there still was a significant amount of diamond still bonded to the stainless steel supports. This delamination can be explained as a stress problem due to the mismatch between the thermal expansions between the porous compacts and the stainless steel supports. It is believed that by improving the heat sink thermal pathway, that such delamination problems can be substantially minimized, if not overcome. Still, the chromium-containing bonding alloy was effective in bonding the two materials to each other. The foregoing data establishes the efficacy of the Cr-containing alloys in bonding thermally-stable compacts to carbide supports.

Claims: A method for fabricating a brazed implement comprised of a compact of self-bonded diamond particles having a network of interconnected empty pores dispersed throughout the compact, the method comprising brazing said compact to another compact or to a cemented carbide support, characterized in that a brazing alloy having a liquidus above 700°C and containing 0 to 35 % by weight of gold and/or silver and 1 to 20 % by weight of chromium is used. The method of claim 1 characterized in that said braze alloy comprises by weight between 20 and 80 percent of palladium, between 2 and 13 percent of chromium, between 1 and 4 percent of boron, and the balance being nickel. The method of claim 1 or 2 characterized in that said carbide support is selected from the group consisting of cemented tungsten carbide, titanium carbide, titanium carbide, tungsten-molybdenum carbide, and tantalum carbide. The method of claim 3, characterized in that the metal bond material for said cemented carbide is selected from the group consisting of cobalt, nickel, iron, and mixtures thereof, an elemental metal which forms a stable nitride or boride, and a metal alloy which forms a stable nitride or boride. The method of claim 4 characterized in that said support comprises cobalt-cemented tungsten carbide. The method of claim 1 characterized in that a disk of said brazing filler metal is interposed between said compact and another compact or a cemented carbide support and then said brazing is accomplished. The method of claim 1 characterized in that said compact is at least partially coated with said brazing alloy which brazes said compact to another compact or to a cemented carbide support. The method of claim 7, characterized in that an additional metal alloy disk is interposed between said coated compact and another compact or carbide support for said brazing process. The method according to anyone of claims 1 to 8 characterized in that said compact is a thermally-stable polycrystalline diamond compact. The method of claim 9 characterized in that said compact comprises 80-90 volume percent self-bonded diamond particles and a second phase of silicon in the form of silicon, silicon carbide, or both. A brazed implement comprising a compact of self-bonded diamond particles having a network of interconnected empty pores dispersed throughout the compact bonded to another of said compact or to a cemented carbide support by brazing filler metal disposed therebetween, characterized in that said brazing metal is an alloy having a liquidus above about 700°C and containing 0 to 35 % by weight of gold and/or silver and 1 to 20 % by weight of chromium. The brazed implement of claim 11 characterized in that said brazing filler alloy comprises by weight between 20 and 80 percent of palladium, between 2 and 13 percent of chromium, between 1 and 4 percent of boron, and the balance being nickel. The brazed implement of claim 11 characterized in that said carbide support is selected front the group consisting of cemented tungsten carbide, titanium carbide, tungsten-molybdenum carbide, and tantalum carbide. The brazed implement of claim 13 characterized in that the metal bond material for said cemented carbide is selected from the group consisting of cobalt, nickel, iron, and mixtures thereof, an elemental metal which forms a stable nitride or boride, and a metal alloy which forms a stable nitride or boride.

Inventors: FLOOD, GARY MARTIN, GIGL, PAUL DONALD, SLUTZ, DAVID EARL, SMITH, GARY WAYNE
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1989
Main classification: B23K31
IPC codes: C04B37, B23K31, B23K1, B23K35