Densification and mechanical properties of mullite-SiC nanocomposites synthesized through sol-gel coated precursors

Mullite-SiC nanocomposites are synthesized by introducing surface modified sol-gel mullite coated SiC particles in the matrix and densification and associated microstructural features of such precursor are reported. Nanosize SiC (average size 180 nm) surface was first provided with a mullite precursor coating which was characterized by the X-ray analysis and TEM. An average coating thickness of 120 nm was obtained on the SiC particles. The green compacts obtained by cold isostatic pressing were sintered in the range 1500–1700°C under pressureless sintering in the N₂ atmosphere. The percentage of the theoretical sintered density decreases with increase in SiC content. A maximum sintered density of 97% was achieved for mullite-5 vol.% SiC. The fractograph of the sintered composite showed a highly dense, fine grained microstructure with the SiC particles uniformly distributed along the grains as well as at the grain boundaries inside the mullite. The Vicker’s microhardness of mullite-5 vol.% SiC composite was measured as 1320 kg/mm² under an applied indentation load of 500 g. This value gradually decreased with an increase in SiC content.