Mechanism of Solid Phase Welding

Abstract

To examine the mechanism of solid phase welding, a pair of polished surfaces of the same or different metals were contacted, and then heated and/or compressed together. In these experiments the following results were obtained. It is necessary for a successful solid phase bonding that interface should be heated above the recrystallization temperature at least of one of the metals by means of heating from surroundings, plastic deformation or friction. Only at higher temperatures than the recrystallization temperature of one of the pair, an exerted pressure can reduce the time required to finish bonding. The friction between the contact surfaces can generate a heat at the interface, and the heat can cause bonding only when the temperature of the heated interface has exceeded the recrystallization temperature or melting point of one of the pair. Crystallographically, the solid phase bonding is affected by the relative magnitude of interface and free surface energies. Namely, the bonding is finished the faster the smaller is the interface energy than the free surface energies of the metals. The strength is affected by the ability of grain growth across the interface. Exerting a pressure can accelerate the diffusion and grain growth across the interface. In metals undergoing solid phase transformation, the boundary at the interface disappears when the bonding temperature has exceeded the critical temperature. That is, in solid phase bonding, the solid phase transformation has the same effects as melting.