Recent developments in high strain rate superplasticity

Abstract

Superplastic forming is an industrial process which is currently limited by the relatively slow strain rates, and consequent long forming times, associated with the fabrication of each superplastic component. Any expansion of this technology requires both the processing of materials capable of exhibiting high strain rate superplasticity (HSR SP) at rates of the order of -10-1-1s-1 and the development of a deeper understanding of the flow mechanisms associated with HSR SP in conventional materials. This paper addresses these problems in two different ways. First, by describing very recent demonstrations of the potential for achieving HSR SP in cast aluminum-based alloys through the use of an intense plastic straining technique to attain an ultrafine grain size. Second, by outlining a procedure for the analysis of HSR SP in metal matrix composites which permits, through the introduction of the concept of load transfer, the possibility of explaining the anomalously high activation energies generally associated with flow in these materials.