Patent GB-878283-A (GB)
Title: Solid-phase bonding of metals
IPC: B23K20/00
Filed: 1958-06-20
Abstract: 878,283. Making composite rods and tubes; welding by pressure; jointing. TEXAS INSTRUMENTS Inc. June 20, 1958 [Oct. 30, 1957], No. 19855/58. Classes 83 (2) and 83 (4). In partially solid phase bonding malleable metal core forming and sleeve forming elements, which are cleaned throughout their surfaces to be interfacially bonded and which has at least one of the surfaces work hardened, the core forming element is coaxially surrounded by sleeve forming material composed at least in an outside part thereof of metal having a lower coefficient of thermal expansion than that of the core forming element, substantially coextensive interfacial contact is established between the outside of the core forming element and an inside part of the sleeve forming material and the assembly is heated at a temperature within the range extending from and including the recrystallization temperature of the metal which has been work hardened or if more than one metal has been work hardened, then from and including the recrystallization temperature of the one with the highest recrystallization temperature and in either case up to but not including the temperature at which liquid phase or a brittle intermetallic compound would appear in the bonding area. In an embodiment the outer surface of a cylindrical copper core 1 and the inner surface of a stainless steel sleeve 3 are cleaned by brushing, wiping, chemical cleaning, etching, pickling, &c. and the core is inserted in the sleeve or the sleeve extruded about the core. In the former case the parts are then brought together by hammering or rolling. The work hardening may be produced by the hammering or rolling or may be produced before assembly by drawing, broaching, extrusion, &c. The assembly is heated in a protective atmosphere furnace, to 1850‹ F. to produce differential expansion between the core and shell and release of energy in the work hardened metal to create a multitude of discrete bonding points for partial bonding. The ends of the sleeve may be sealed around the ends of the core by pinching the ends 7, Fig. 2, and welding at 9. In this case heating in a non-protective atmosphere may or may not be employed. The partially bonded assembly is mechanically reduced with or without cooling the assembly, by drawing it in one or more passes through a drawing die at a temperature below the recrystallization temperature of the component having the highest recrystallization temperature and below a temperature at which a liquid phase or a brittle intermetallic compound would form. Then the assembly is heated at a temperature 1850‹ F. which will recrystallize at least one of the metals to increase the bond strength by causing lateral growth and diffusion of the partial bonds. The core and sleeve may be respectively of copper and nickel; brass and alloy of gold, copper, zinc and nickel or of silver and brass. To bond a shell 13, Fig. 3, e.g. of copper or an alloy of gold, copper, silver, zinc and nickel, having a coefficient of expansion higher than or equal to that of the core 11, e.g. of nickel to the core, the assembly of core and shell is surrounded by a jacket 17, e.g. of steel, having a coefficient of expansion lower than that of the core. A parting compound such as graphite or milk of magnesia may be provided between the jacket and shell or the jacket may be cleaned if it is to be bonded to the shell. This assembly may be pinched and welded as before. The assembly is hamniered or rolled and heated as before to effect partial bonding. The jacket, if it is not to be bonded, may be removed before or after the final bonding by slitting, peeling or chemical dissolution. The partially bonded assembly is reduced and heated to effect final bonding as described above. The elements may be of ovate, polygonal, crescent or petaliform cross-section and the core may be hollow. Specifications 745,426 and 867,994 are referred to.