The Kinetics of Isothermal Martensitic Transformation of Zirconia Containing a Small Amount of Yttria

The high temperature tetragonal phase of zirconia containing 1.40-1.60 mol% Y 2 O 3 were successfully quenched in at room temperature by rapid cooling of small spherical specimens. On these metastable specimens, the isothermal transformation behavior into the monoclinic phase was studied by dilatometric method. The transformation start time exhibited a C-curve in a TTT diagram. The C-curve shifted toward short time side as well as toward high temperature side with decreasing yttria content or increasing grain sizes. A study of the pre-aging effect during the incubation period on the subsequent isothermal transformation suggested consecutive growth of embryos, but alternative interpretation was also possible. The activation energy was evaluated to be $50 kJ/mol