Isothermal tetragonal-to-monoclinic phase transformation in Y2O3-partially stabilized zirconia:: The influence of grain size

Phase transformation in ZrO2-2mol% Y2O3 ceramics, with average grain sizes of 0.51 to 0.96 mum, was investigated to explore the influence of grain size on isothermal phase transformation associated with the low-temperature degradation during ageing in different environments (water and vacuum). Contrary to expectations, water-assisted phase transformation did not accelerate monotonously with increasing grain size. Such interesting results can be explained satisfactorily by a new model of phase transformation, which emphasises a synthetic grain-size effect on the nucleation process and the intrinsic phase stability.