Structure and Thermomechanical Properties of Partially Stabilized Zirconia in the CaO‐ZrO ₂ System

Partially stabilized zirconia (PSZ) ceramics in the system CaO‐ZrO 2 were characterized. The microstructure, as revealed by optical microscopy, consisted of grains of pure ZrO 2 distributed in a matrix of fully stabilized material. Electron microscopy showed that the matrix grains have a complex substructure of 1000‐Å domains of cubic and monoclinic ZrO 2 . The grains appeared to fit Ubbelohde's concept of a hybrid single crystal. Evidence obtained indicated that the substructure provides an effective stress‐relieving mechanism during thermal shock. It is proposed that initiation of phase inversion in pure ZrO 2 domains, even at subtransition temperatures (by thermal stresses), creates an extremely large microcrack density. On the basis of Hasselman's thermal‐shock criterion, only quasi‐static crack propagation occurs during thermal shock of PSZ; evidence is presented to support this concept.