Isothermal and athermal martensitic transformations in a zirconia–yttria alloy

The Ms (martensite start temperature) of the tetragonal to monoclinic (t–m) transformation in the ZrO2–Y2O3 system has been measured for bulk specimens as a function of Y2O3 composition. It decreased nearly linearly with increasing Y2O3 content up to 1.75 mol.%, but the transformation suddenly ceased to exist beyond 2.0 mol.% of Y2O3. The Ms showed a tendency to be suppressed by rapid cooling. In fact with a small specimen containing 1.6 mol.% of Y2O3, the transformation was completely suppressed by water quenching. The highly unstable tetragonal specimen prepared by such a method was found to exhibit both an isothermal transformation at elevated temperature and an athermal transformation during subzero cooling to liquid nitrogen temperature. The C-curve for the isothermal transformation and the Ms temperature for athermal transformations were obtained.