THE BEHAVIOR OF METAL MATRIX COMPOSITES DURING TEMPERATURE CYCLING

Commercial purity aluminium reinforced with SiC particles has been used to model the behaviour of metal matrix composites (MMCs) during thermal cycling. Above a critical temperature amplitude of about 150-degrees-C an acceleration in creep under the load occurs. This is accompanied by a reduction in the creep stress exponent n from 15 to 1. The reduced stress exponent leads to a superplastic deformation behaviour with extension in excess of 150% recorded. Transmission electron microscopy studies of the deformed microstructures show an essentially constant dislocation structure between as-received MMCs and those after 90% strain. The deformation microstructures were free of substructures such as polygonised cells characteristic of the recovery creep in monolithic alloys.