Microstructural development in partially stabilized ZrO2 in the system CaO--ZrO2

The microstructures of 3 zirconias partially stabilized with CaO were investigated using scanning electron microscopy and qualitative and quantitative X‐ray analysis. The structure was closely related to the heat treatments involved in fabrication. A bimodal structure with small grains of pure ZrO 2 dispersed along the grain boundaries of larger cubic solid‐solution grains developed during slow cooling from 1850° to 1300°C. The presence of a liquid phase greatly enhances the growth of the pure ZrO 2 phase. An anneal at 1300°C induces precipitation of fine ZrO 2 particles within the solid‐solution grains. The relative mechanical strengths of the materials are explained in terms of the weakening of the grain boundaries associated with the transformation of the grain‐boundary phase on cooling.