Fracture behaviour of magnesia and magnesia–spinel composites before and after thermal shock

Microstructural changes, as a consequence of the thermal expansion mismatch between magnesia and spinel phases, and fracture behaviour of magnesia and spinel composites have been investigated as a function of spinel content (10, 20, 30 wt.%). Fracture surfaces of magnesia showed mostly transgranular fracture; for the composites, however, the amount of intergranular fracture increased with increasing spinel content. This change in fracture behaviour is thought to be the main reason for the increase in the work of fracture, γWOF. The 30% spinel composite was found to exhibit both the greatest resistance to crack propagation, and the greatest resistance to thermal shock damage, with the highest retained strength after quenching.