THE CHARACTERISTICS OF MICROCAVITATION IN HIGH-STRAIN RATE SUPERPLASTICITY

Experiments were conducted on an Al-2124 composite reinforced with Si3 N4 particulates under conditions appropriate for optimum high strain r ate superplasticity (HSR SP) and at a temperature where there is exper imental evidence for partial melting. It is shown that small but stabl e microcavities, having diameters of < 1 mu m, are formed in the compo site during deformation under these conditions. These microcavities ar e nucleated relatively easily at the interfaces between the reinforcem ent and the matrix alloy but the growth of the cavities along the inte rfaces is very slow because the presence of a liquid phase serves to r elax the stress concentrations and, in addition, the process of plasti city-controlled growth is partially inhibited because the cavities imp inge on the Si3N4 particulates. Quantitative measurements show that th e orientations of the cavities are random with respect to the tensile axis. (C) 1998 Elsevier Science S.A. All rights reserved.