FABRICATION OF SAPPHIRE FIBER-REINFORCED CERAMIC-MATRIX COMPOSITE

A combination of pressure filtration and reaction sintering techniques has been used for the fabrication of a fibre reinforced ceramic matri x composite. Large diameter (nominally 125 mu m) zirconia coated Saphi kon monofilament sapphire fibre reinforcements were incorporated in a reaction sintered mullite matrix. Matrix formation was achieved by oxi dation of beta silicon carbide to a cristobalite at 1250 degrees C and subsequent mullitisation with ex alumina at 1550 degrees C, optimisat ion of the matrix being achieved by study of the consolidation behavio ur before fibre inclusion. Testbars exhibiting small dimensional chang es after sintering have been produced with a relative density of appro ximately 96%. Young's modulus measurements were performed employing a forced resonance method in air and under vacuum. This testing method e nabled changes in the elastic properties to be monitored in relation t o matrix development during sintering, and with the addition of reinfo rcing fibres. The fracture behaviour of the composites was evaluated, and showed, to some extent, typical composite failure patterns.