Stability of Tetragonal ZrO₂ Particles in Ceramic Matrices

The stability of tetragonal ZrO₂ particles in ceramic matrices was considered, with particular reference to Al₂O₃‐ZrO₂ composites and to partially stabilized ZrO₂. In both systems, particles above a “critical” size transform martensitically to monoclinic symmetry on cooling to room temperature. The critical factors that could affect the size dependence of the transformation temperature—surface and strain energy effects, the chemical free energy driving force, and the difficulty of nucleating the martensitic transformation—were considered. Nucleation arguments are probably the most important.