FRACTURE TOUGHNESS OF SiC WHISKER REINFORCED Si3N4 CERAMICS.

Fracture toughness for Si//3N//4 composite containing 0-30 wt% SiC whisker was measured by Indentation Microfracture and Chevron Notch methods. The results indicate that fiber reinforcement with whisker is an effective way to toughen Si//3N//4 ceramics. Microscopic observations of the cracks induced by indentation showed that the crack propagation is often prohibited by the whisker, and that the crack is deflected to the interface between the whisker and the matrix. This crack deflection may be attributed to the stress fields set up at the interface, due to thermal expansion difference between the whisker and matrix. Considering such crack-whisker interaction, it is suggested that the dispersion of the whisker having large diameter is effective intoughening Si//3N//4 ceramics.