Low-temperature ageing of zirconia-toughened mullite composites

The change of mechanical properties of zirconia-toughened mullite composites, aged at low temperature in air, was investigated in this paper. The results indicated that the existence of microcracks, which were formed by the transformation of the zirconia tetragonal phase to the monoclinic during the cooling stage of processing was an important factor for the degradation of mechanical properties during subsequent ageing at 200–300°C. The increasing of flexural strength of the composites aged at 500–600°C was attributed to the relaxation of stress by reverse transformation of ZrO₂.