EFFECT OF HOT-PRESSING TIME AND POST-HEAT TREATMENT ON THE MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SIC-FIBER-REINFORCED GLASS-CERAMIC COMPOSITES

Nicalon-SiC-fibre-reinforced (35 vol %) lithium-aluminosilicate (LAS) glass-ceramic composites were fabricated by a slurry-infiltration process followed by hot pressing at 1400-degrees-C and 10 MPa for varying soaking times. The ultimate strength and elastic modulus of the as-fabricated composites, as determined by four-point flexural tests, increased rapidly with the densification time, saturating after 30 min at 550 MPa and 130 GPa, respectively. Longer hot-pressing times caused a decrease in the elastic modulus via fibre degradation. A carbon-rich interfacial layer formed between the fibres and the matrix, the thickness of which reached a maximum of approximately 400 nm after approximately 30 min soaking time. The flexural strength of post-heat-treated composites in air decreased by a factor of approximately four, due to oxidation and removal of the carbon content of the interfacial layer. The silica-rich bridges left behind between the fibres and the matrix contributed to brittle fracture of the composite.