SIC FIBER-REINFORCED LITHIUM ALUMINOSILICATE MATRIX COMPOSITES FABRICATED BY THE SOL-GEL PROCESS

Abstract

SiC fibre-reinforced lithium aluminosilicate (LAS) matrix composites were fabricated by (i) the hydrolysis-condensation reaction of relevant metal alkoxides, and (ii) the non-aqueous condensation route using diphenylsilanediol. Optimum reaction conditions of LAS sol formation for thin coating applications in the hydrolysis-condensation route were derived from theological measurements. The SiC fibre-LAS composite fabricated by the hydrolysis-condensation route shows a uniform microstructure. The debonding/fibre pullout was more pronounced in the niobium-doped composites. The fracture toughness, K-1c, also increased from 11 MPam(1/2) for the undoped composite to 16 MPam(1/2) for the 5 wt% Nb-doped composite, suggesting that the fibre pullout contributes significantly to the toughening of SiC fibre-LAS composites. The crystallization of matrix at high temperatures (after hot pressing at 800 degrees C) eroded SiC fibres internally. This was attributed to the diffusion of aluminium atoms into the fibre, forming aluminium carbide above 1200 degrees C.