Effects of noncompositional inhomogeneity on t → m phase transformation during grinding of various rare-earth-doped zirconias

The phase transformation from metastable tetragonal (t) into monoclinic (m) phase must be studied using samples that are homogeneous in their compositions and microstructures. This paper reports that the present study investigated the transformability by grinding for compositionally homogeneous samples prepared by rapid quenching of melts in the system ZrO2-RO1.5 (R:Nd, Sm, Y, Er, Yb). The volume fraction of m-phase Vm(tg) against grinding time tg was investigated using powder x-ray diffraction for the rapidly quenched sample. The Vm(tg) value increased with grinding time tg, then saturated to a certain value Vm(∞) of between 1 and 0 when it was ground and crushed for a long time. Both the transformation rate (dVm/dtg)tg = 0 and the saturated value Vm(∞) decreased with dopant content X. The species of dopants had less influence on the transformability. The experimental Vm(∞) and Vm(0) data could be explained using a model which has a normal distribution of effective free energy change between t and m phases, ΔGt-m, among hypothetical parts of the sample