The effect of processing on the mechanical properties and interfacial strength of aluminium/TiC MMCs

The microstructure and mechanical properties of aluminium/TiC MMCs made by powder processing (PM), by a flux-casting process, and by melting PM material, have been compared. Particle clustering is more prevalent in cast than in PM composites, but the grain-refining nature of TiC particles significantly reduces the degree of clustering commonly observed in cast MMCs. Melting PM material enables oxide films to 'trawl' the particles into large clusters. The stiffness and ductility are similar for cast and the PM composites but melting the PM material results in significant reductions in strength and ductility. In all cases, composite ductility is enhanced by extrusion through the removal of porosity and the break-up of particle clusters. Modulus measurements as a function of plastic strain indicate that rates of damage accumulation are lowest, and hence interfacial bonding is strongest, in cast composites as a result of the attainment of intimate contact and strong chemical bonding between the two phases. (C) 2000 Elsevier Science Ltd. All rights reserved.