ANOMALOUS PENETRATION OF AL INTO SIC

The chemical composition of a SiC/Al interface was investigated after two different annealing conditions. The composite was produced by powder metallurgy methods and it showed remarkable interfacial stability in the as-prepared condition; similar results were obtained as long as the annealing temperature was kept below 650 degrees C. On the other hand, substantial interpenetration was seen when the Al matrix was present in the liquid state. At temperatures above 700 degrees C, the interface was seen to react quite rapidly and to be covered with a thick layer of Al4C3; while, at 680 degrees C, the interface acquired a serrated profile along the basal planes of the SiC and substantial amounts of Al were seen to penetrate into the SiC along channels formed due to the break up of the SiC. In such cases, no Al4C3 was seen to precipitate in the matrix; instead, MgAl2O4 and Al2O3 were observed but at distances up to 100 nm away from the interface.