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 ZrO₂ 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 ZrO₂ phase. An anneal at 1300°C induces precipitation of fine ZrO₂ 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.