INTERFACES IN CAST METAL-MATRIX COMPOSITES

A detailed analysis of possible interfaces in cast aluminum silicon ba se reinforced particle composites containing SiC, Al2O3 and C indicate s that several different kinds of interfaces can form. The reinforceme nts may be totally surrounded by primary-phase, or primary silicon, or by the eutectic between Al and Si. In addition, some of the original coatings or their reaction products in the case of coated particles (s uch as nickel or nickel-aluminum intermetallics in nickel coated reinf orcements Cu or Cu-aluminum intermetallics in Cu coated reinforcements ) may also form the interface. The reaction between dispersoids and th e alloy itself can form a complex interface. These different interface s have also been experimentally observed in the microstructures of cas t particulate composites, with the exception of primary alpha-aluminum surrounding the reinforcement. The absence of alpha-aluminum on the r einforcements is attributed to possible lack of nucleation, persistent lateral growth and a thermal lag between the reinforcement and the ma trix. Estimates of works of adhesion for the different interfaces obse rved in cast composites have been made using London-van der Waal equat ion, correlated to the properties of the composites, and used to ident ify the possibilities of further improving these properties.