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 as sociated microstructural features of such precursor are reported. Nanosize SiC (average size 180 nm) surface was first provided with a mullite precurs or coating which was characterized by the X-ray analysis and TEM. An averag e coating thickness of 120 nm was obtained on the SiC particles. The green compacts obtained by cold isostatic pressing were sintered in the range 150 0-1700 degreesC under pressureless sintering in the N-2 atmosphere. The per centage 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 Vicke r's microhardness of mullite-5 vol.% SiC composite was measured as 1320 kg/ mm(2) under an applied indentation load of 500 g, This value gradually decr eased with an increase in SiC content.