Effect of thermal residual stress on the high temperature toughening behaviour of TiB2/SiCw composites

SiC-whisker-reinforced TiB2 composite was produced by hot pressing techniques. The composite exhibited superior mechanical properties at room temperature compared to those of monolithic TiB2, especially in respect of the fracture toughness, KIC, which was approximately 115% higher than that of TiB2 ceramic without SiC whiskers, the maximum values of the fracture toughness and flexural strength being 7.3 MPa m and 640 MPa, respectively. Considerable improvement in the high-temperature fracture toughness of the composite was observed up to 1200°C. Based on the thermal residual stress analysis and fracture surface observations, the fracture toughness at high temperature was correlated with the change in inequality between the whisker fracture strength and the compressive clamping forces on the whiskers caused by thermal expansion mismatch between the whiskers and the matrix. The results showed that the number of whiskers pulled out depends greatly on the test temperature, the whisker aspect ratio and the interfacial friction coefficient. At high temperature the whiskers are mainly pulled out, whilst at low temperature the whiskers are mainly fractured.