SOLIDIFICATION OF PARTICLE-REINFORCED METAL-MATRIX COMPOSITES

The solidification behavior of ceramic particle-reinforced metal-matri x composites (MMCs) is different from that of the bare matrix, not onl y because of the presence of the ceramic particles, but also due to th eir redistribution in the melt that results in nonhomogeneous thermoph ysical properties. The MMCs comprised of 10- to 15-mu m SiC particles of varying volume fractions, dispersed uniformly in a modified aluminu m A356 alloy by the melt stirring technique, were solidified unidirect ionally in a thermocouple-instrumented cylindrical steel mold. The coo ling rates were continually monitored by measuring temperatures at dif ferent depths in the melt, and the solidified MMCs were sectioned into disks and chemically analyzed for SiC volume fraction. The results po int out that the cooling rate increased with increasing volume fractio n of SiC particles. A small increase in the bulk SiC volume fraction o f the cast MMC was observed due to particle settling during solidifica tion. A one-dimensional enthalpy model of MMC solidification was formu lated, wherein particle settling occurring in the solidifying matrix w as coupled to the enthalpy equation by means of the Richardson-Zaki hi ndered settling correlation. A comparative study of simulations with e xperiments suggested that the thermal response of SiC particles used i n this study was similar to that of single crystals, and their presenc e increased the effective thermal conductivity of the composite.