Method of brazing

Abstract: A tool component comprises an abrasive compact (10) bonded to a support (12) which itself is bonded through an alloy (16) to an elongate cemented carbide pin (14). The alloy has a liquidus below 900°C and the following composition, by weight: Mn 15 - 41% Cu 67 - 41% Ni 1 - 5% Au 10 - 17% The shear strength of the bond achieved between the support (12) and the pin (14) exceeds 345 MPa.

Description: BACKGROUND OF THE INVENTION This invention relates to a method of bonding a cemented carbide surface to a metal containing surface and in a preferred embodiment to a method of forming a composite abrasive compact in said manner. Abrasive compacts are well known in the art and are used for a variety of abrading operations such as cutting, drilling, grinding, and the like. Abrasive compacts consist of a polycrystalline mass of bonded abrasive particles, the abrasive particle content of which is at least 70 percent by volume, and generally 80 to 90 percent by volume. The abrasive particles may be self-bonded without the aid or use of a second or bonding phase. Alternatively, a second or bonding phase may be provided. The abrasive particles for compacts are invariably diamond or cubic boron nitride. Abrasive compacts may be bonded to cemented carbide supports. Such bonded compacts are often referred to as composite compacts. Bonding between the compact and the carbide support may be direct, i.e. without the interposition of a braze layer. Alternatively, a bonding braze layer may be provided between the compact and the carbide support. A more detailed description of abrasive compacts and composite abrasive compacts may be found in a number of published patent specifications, for example, United States Nos. 3,743,489, 3,767,371, 4,063,909 and 3,745,623. Rotary drills used for oil and gas well drilling and core drilling generally comprise a drill bit having formed thereon a plurality of pre-formed sockets in which cutting elements or components are mounted. The cutting elements or components may be brazed, force-fitted or heat shrunk into the sockets. Typical cutting elements used in the prior art are steel teeth, steel teeth laminated with tungsten carbide, inserts of cemented tungsten carbide, natural diamonds and composite abrasive compacts. Cutting components for drill bits and utilising composite compacts have been described in the literature and have been used commercially. Such cutting components comprising an elongate pin of cemented carbide to which is bonded a composite compact, bonding being achieved through the carbide support of the composite compact. Bonding between the carbide support and the elongate pin is achieved by braze metal which has a melting point above 700°C. Such a high temperature braze, so the art teaches, is essential in order to achieve a sufficiently strong bond between the composite compact and the elongate pin. Reference in this regard may be had to disclosures of United States Patent No. 4,225,322. The braze which is said in this patent specification to be useful is Anaconda 773 which is now thought to be undesirably reactive with the carbide pieces being joined. European Patent Publication 213,300 and United States Patent No. 4,527,998 describe braze alloys for bonding composite abrasive compacts to elongate pins which are said to have advantages over Anaconda 773. The alloy of the European publication contains palladium, chromium, boron and nickel while the alloy of the United States patent contains gold, nickel, palladium, manganese and copper. The braze alloy of US-A-4 527 998 has the following composition, by weight: Au 18-39.5% Ni 3.5-14.5% Pd 2.5-10.5% Mn 7.5-9.0% Cu Balance. US-A-3 928 029 discloses a brazing alloy for brasing of high performance structural materials such as turbine or compressor components, the alloy comprising, in percent by weight, from about 49 to 58 percent copper, about 25 to 32 percent manganese, about 2 to 10 percent nickel, and about 7 to 16 percent gold. Alloy B of Tables I and II thereof, comprising 54% Cu, 28% Mn, 2% Ni and 16% Au by weight, is stated to have a liquidus temperature of 941°C (1725°F). Tool components are also available and used which comprise two carbide bodies bonded together or a carbide body bonded to a steel or like body. Strong bonds between such bodies are desirable. SUMMARY OF THE INVENTION According to the present invention, there is disclosed in Claim 1 a method of bonding a cemented carbide surface to a metal containing surface including the steps of placing a layer of a braze alloy between the surfaces, the alloy having the following composition, 15 - 41% Mn, 67 - 41 % Cu, 1 - 5% Ni and 10 - 17% Au, all percentages by weight, urging the surfaces together, and raising the temperature of the alloy to its working temperature thereby creating a bond between the surfaces which has a shear strength exceeding 345 MPa. Preferred embodiments of the invention are disclosed in dependent Claims 2 - 11. DESCRIPTION OF THE DRAWING The drawing illustrates a partially sectioned perspective view a composite abrasive compact formed according to the method of the invention. DETAILED DESCRIPTION OF THE INVENTION Essential to the invention is the choice of the braze alloy which has a liquidus below 900°C and which produces a bond strength exceeding 345 MPa. This braze alloy allows for a strong bond between the surfaces to be created at a low temperature. Preferably the shear strength of the bond between the surfaces is 415 MPa or higher. The liquidus temperature of the braze alloy is that temperature at which the alloy starts to melt. The working temperature is that temperature at which substantially all the alloy is in a molten state and is somewhat higher than the liquidus temperature. Generally the working temperature will be 30 to 50°C higher than the liquidus temperature. The metal containing surface will generally also be a cemented carbide surface. The cemented carbide may be any known in the art such as cemented tungsten carbide, cemented tantalum carbide, cemented titanium carbide, or mixtures thereof. The cemented carbide surface will preferably have an abrasive compact bonded to it. The degradation temperature of the abrasive compact is preferably at or above the working temperature of the alloy. The degradation temperature of the abrasive compact is that temperature at which substantial degradation of the abrasive particles of the compact occurs. The abrasive compact is preferably a diamond abrasive compact. The method of bonding the cemented carbide surface to the other surface constitutes another aspect of the invention and will be described with reference to the drawing. A composite abrasive compact comprising an abrasive compact layer 10 bonded to a cemented carbide support 12 is provided. There is also provided an elongate cemented carbide pin 14. A layer 16 of the braze alloy is placed between the upper flat surface 18 of the pin 14 and the lower flat surface 20 of the support 12. The alloy layer 16 makes contact with both the surfaces 18 and 20. These surfaces are then urged together, for example by means of a suitable clamp or load otherwise applied. The temperature of the braze layer is raised to its working temperature. The alloy may be raised to its working temperature over a period of 5 to 20 minutes in a furnace. Alternatively, localised heating such as induction heating may be used in which case the temperature will be raised over a much shorter period, e.g. less than 150 seconds. A bond having a shear strength exceeding 345 MPa is created between the support and the substrate without any significant degradation to the abrasive compact occurring. It has been found that the bond strength can be improved if the alloy, prior to being placed between the surfaces, is heat treated at a temperature below its liquidus temperature for a period not exceeding 30 minutes in an atmosphere selected from inert, reducing and non-oxidising atmospheres. Typically the heat treatment of the alloy is carried out at a temperature of 700 to 850°C. The atmosphere is typically argon or hydrogen. This improved bond strength is particularly surprising as heat treatment does not appear to have a similar effect on the alloy described in U.S. Patent No. 4,527,998. In an example of the invention, a composite diamond abrasive compact consisting of a diamond abrasive compact having a degradation temperature exceeding 915°C bonded to a cemented tungsten carbide support was bonded to a cemented carbide substrate using a braze alloy which had the following composition, by weight: Cu 53% Mn 29% Au 14,5% Ni 3,5% The liquidus temperature of this alloy is 880°C and its working temperature is 915°C. The braze alloy was sandwiched between the cemented carbide support of the composite diamond abrasive compact and the cemented carbide substrate and a load applied to urge the two surfaces together. The temperature of the braze alloy was raised over a period of 10 minutes to a temperature of 915°C and held there for 3-4 seconds. Heating took place in a furnace. After heating, the bonded assembly was removed from the furnace. It was found that a strong bond having a shear strength of the order of 378 MPa was produced between the composite diamond abrasive compact and the substrate. A similar composite abrasive compact was produced except the alloy in this case was heated at 800°C for 20 minutes in a hydrogen atmosphere prior to being placed between the two carbide surfaces. The shear strength of the bond was found to be 460 MPa. A third composite abrasive compact was produced in a similar manner and using the same heat treated alloy and the shear strength of the bond was found to be 468 MPa. A composite abrasive compact as described above was produced using a braze alloy RI 46 which had a liquidus temperature of 971°C and the following composition, by weight: Au 34,5% - 36,0% Ni 13,5% - 14,5% Pd 9,5% - 10,5% Mn 9,0% - 10,5% Cu Balance The shear strength of the bond was found to be 647 MPa which, as expected, was higher than the shear strengths achieved using the braze alloys of the present invention because it was a higher melting alloy. However, heat treatment of the braze alloy in the manner described above had no effect on the shear strength of the bond obtained.

Claims: A method of bonding a cemented carbide surface to a metal containing surface including the steps of placing a layer of a braze alloy between the surfaces, the alloy having the following composition, 15 - 41% Mn, 67 - 41% Cu, 1 - 5% Ni and 10 - 17% Au, all percentages by weight, urging the surfaces together, and raising the temperature of the alloy to its working temperature thereby creating a bond between the surfaces which has a shear strength exceeding 345 MPa. A method according to claim 1 wherein the temperature of the alloy is raised to its working temperature over a period of 5 to 20 minutes. A method according to claim 1 or claim 2 wherein the alloy is raised to its working temperature over a period which does not exceed 150 seconds. A method according to any one of claims 1 to 3 wherein the cemented carbide surface is a surface of a cemented carbide support to which is bonded an abrasive compact, the degradation temperature of which is at or above the working temperature of the alloy. A method according to claim 1 wherein the abrasive compact is a diamond abrasive compact. A method according to any one of claims 1 to 5 wherein the metal containing surface is a cemented carbide surface. A method according to any one of claims 1 to 6 wherein the carbide is selected from titanium carbide, tantalum carbide, tungsten carbide and mixtures thereof. A method according to any one of claims 1 to 7 wherein the bond created between the surfaces has a shear strength of 415 MPa or higher. A method of any one of claims 1 to 8 wherein the alloy has the following composition, by weight: Cu 53% Mn 29% Au 14,5% Ni 3,5% A method according to any one of claims 1 to 9 wherein the alloy, prior to being placed between the surfaces, is heat treated at a temperature below its liquidus temperature for a period not exceeding 30 minutes in an atmosphere selected from inert, reducing and non-oxidising atmospheres. A method according to claim 10 wherein the heat treatment of the alloy is carried out at a temperature of 700°C to 850°C.

Inventors: PIPKIN NOEL JOHN, TANK KLAUS, PIPKIN, NOEL JOHN, TANK, KLAUS
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1988
Main classification: B23K35
IPC codes: E21B10, B23K35, B24D3, B23K31, C22C9, B23K1, C22C30