Work of fracture and fracture surface energy of magnesia-spinel composites

This study used a model system of fully dense high purity magnesia, incorporating fine grain spinel prepared by hot-pressing. Work of fracture ( γ WOF) and fracture surface energy ( γ i ) were determined to be a function of spinel particle size and volume fraction. Predictions made from the thermal shock parameter, R⁗, were tested by measurements made on γ WOF γ i ratios of magnesia and magnesia-spinel composites. The results obtained from γ WOF γ i ratios matched the predictions. On the basis of γ WOF γ i ratios, the optimum spinel content and particle size were determined. Thermal shock data confirmed that higher values of the γ WOF γ i ratios were considered to be a good indicator for thermal shock resistance. Higher values of γ WOF were associated with the occurrence of more intergranular fracture with increasing spinel additions. Crack propagation was found to be much more difficult in magnesia-spinel composites, than the initiation of cracks.