The present invention relates to thermally stable polycrystalline diamond compacts and more particularly to brazing such compacts to cemented carbide supports and to themselves.
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. Pat. Nos. 3,745,623 and 3,608,818 with respect to polycrystalline diamond compacts and U.S. Pat. Nos. 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.degree. C., did limit their usefulness, especially in metal matrix bond applications. Thermal stability of such polycrystallline 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. Pat. Nos. 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 No. 8508295 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, British Pat. No. 2,163,144 reognizes 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 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.degree. 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. Pat. Nos. 3,894,673 and 4,018,576 propose to bond signle crystals of diamond to metal using nickel/chromium or cobalt/chromium braze alloys.