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

In a previous paper (Demir, A. and Thompson, D. P., Heat-treatment of Nicalon SiC fibres in various atmospheres and pressures. In Proc. 3rd Int. Turkish 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 of Nicalon SiC fibres resulted in significantly improved strength and refractoriness, and at the same time deposited a thin carbon coating on the surface of the fibres. In the present study, fibres heat-treated in this way have been used to reinforce a range of β-sialon ceramic matrices, and the resulting mechanical properties (bend strength, fracture toughness) have been compared with results for similar materials prepared from non-heat-treated Nicalon fibres. All samples showed significant increases in strength and density, with in general, not much change in fracture toughness. The presence of the coating on the fibres assisted the densification of the composites by decreasing friction during hot-pressing, thereby increasing density and matrix strength. SEM micrographs indicated that the carbon coating is still present after fabrication and is sacrificed during fracture, assisting in easy pull-out of fibres.