Effect of limited matrix-reinforcement interfacial reaction on enhancing the mechanical properties of aluminium-silicon carbide composites

An unconventional approach to strengthening Al/SiC composites through controlled matrix-reinforcement interfacial reactions was studied. Composites with two distinct interfacial microstructures were prepared by varying the contact time between the SiC particles and molten aluminium during processing. The formation of a thin Al4C3 reaction layer along the particle-matrix interface was found to increase the composite yield strength, ultimate tensile strength, work-hardening rate and work-to-fracture, and change the fracture pattern from one involving interfacial decohesion to one where particle breakage was dominant. These changes were attributed to a stronger interface bond, which is thought to result from the tendency for the Al4C3 reaction layer to form semicoherent interfaces and orientation relationships with the aluminium matrix and SiC particles and for it to be mechanically keyed-in to both these phases. The stronger interface bond also enhanced the levels of plastic constraint which, when coupled with the greater work hardening, promoted local matrix failure, thereby reducing the composite ductility. (C) 2001 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.