Densification and microstructural developments during the sintering of aluminium silicon carbide

Densification and microstructural developments during the sintering of aluminum silicon carbide (Al4SiC4) were examined. Two types of Al4SiC4 powders were prepared by the solid-state reactions between: (i) Al, Si, and C at 1600°C for 10 h (designated as Al4SiC4(SSR)), and (ii) chemically-vapour deposited ultrafine Al4C3 and SiC powders at 1500°C for 4 h (Al4SiC4(CVD/SSR)). The specific surface areas of the Al4SiC4(SSR) and Al4SiC4(CVD/SSR) powders were 2.7 and 15.5 m2 · g−1, respectively. Relative densities of the pressureless-sintered Al4SiC4(SSR) and Al4SiC4(CVD/SSR) compacts were as low as 60–70% for firing temperatures between 1700°C and 2000°C. The relative densities of Al4SiC4(SSR) and Al4SiC4(CVD/SSR) compacts could be enhanced using the hot-pressing technique; the relative density of the Al4SiC4(SSR) compact hot-pressed at 1900°C for 3 h was 97.0% whereas that of the Al4SiC4(CVD/SSR) compact hot-pressed at 1900°C for 1 h attained 99.0%. The former microstructure was composed of plate-like grains of width 10–30 μm and thickness ∼10 μm whilst the latter microstructure was comprised of equiaxed grains with a typical diameter of ∼10 μm. Densification of the Al4SiC4(CVD/SSR) compacts appeared to be promoted compared to the Al4SiC4(SSR) compact and this was attributed to the higher surface area, reduced agglomeration of the starting primary particles, and more homogeneous chemical composition.