Accelerated Diffusion Bonding Using Induced Forces

Abstract

Classical diffusion bonding has always connoted nonproduction-like conditions such as extremely high pressures for long times, protective environments, and excessive cleanliness requirements. The attractive characteristics are that diffusion bonds are normally produced at comparatively low temperatures and they have parent metal properties. This paper presents a technique whereby high pressures are selectively applied to the interfacial region of the two parts being joined at temperatures approximately 90–95 percent of the parent metal melt range. The parts to be joined are heated rapidly using “induction heating” techniques. The mating surfaces and the areas immediately adjacent to them are the only portions of the parts that are significantly heated in most applications. As soon as the proper temperature range has been reached, the heating current is shut off and an intense magnetic field is forced or driven through the parts. The orientation and direction of this moving magnetic field is such that a large pulsed current is caused to flow on both sides of and parallel to the interface. These large currents attract each other and give rise to substantial pressures normal to the interface, thereby producing intimate contact on a microscopic scale, allowing for rapid diffusion. There is also some preferential super heating in the interfacial zone for a few milliseconds only but greatly enhancing diffusion conditions. Results of the application of this technique to several material combinations are discussed along with photomicrographs of joined sections.