Growth and microstructure of Al₂O₃-SiC-Si(Al) composites prepared by reactive infiltration of silicon carbide preforms

Abstract

Alumina matrix composites have been grown by directed melt oxidation of an Al-Si-Zn-Mg alloy into sintered SiC preforms. Reaction between melt and the silica layer on the pre-oxidised SiC yields a matrix in which the residual alloy is principally silicon. However, there is no evidence of the formation of Al₄C₃. The coarsest particles display the least reaction while porosity increases as the particle size decreases .Thus, owing to the enrichment of silicon, growth rates are retarded compared to those in free space. The microstructure of the oxide is monocrystalline over distances of the order of the inter-particle spacing, however, a new type of growth fault that constitutes an inversion boundary in the Al₂O₃, has been found. Owing to the substantial reaction between the particle and the melt, the volume fraction of the alloy constituent in the final composite depends sensitively on particle size, in contrast to its relative invariance in directed melt oxidation into inert preforms.