High-performance SiC-fibre reinforced beta-sialon CMCs prepared from heat-treated Nicalon fibres

In a previous paper (Demir, A. and Thompson, D. P., Heat-treatment of Nical on SiC fibres in various atmospheres and pressures. In Proc. 3rd Int. Turki sh Ceramic Congress, Vol. 2, Engineering Ceramics, ed. V. Gunay, H. Mandal and S. Ozgen. Turkish Ceramic Society, Istanbul, 1996, pp. 180-185) it was reported that a high-pressure, high-temperature carbon monoxide treatment o f Nicalon SiC fibres resulted in significantly improved strength and refrac toriness, and at the same time deposited a thin carbon coating on the surfa ce of the fibres. In the present study, fibres heat-treated in this way hav e been used to reinforce a range of beta -sialon ceramic matrices, and the resulting mechanical properties (bend strength, fracture toughness) have be en compared with results for similar materials prepared from non-heat-treat ed Nicalon fibres. All samples showed significant increases in strength and density, with in general, not much change in fracture toughness. The prese nce of the coating on the fibres assisted the densification of the composit es by decreasing friction during hot-pressing, thereby increasing density a nd matrix strength. SEM micrographs indicated that the carbon coating is st ill present after fabrication and is sacrificed during fracture, assisting in easy gull-out of fibres. (C) 2001 Elsevier Science Ltd. All rights reser ved.