Structure and Thermomechanical Properties of Partially Stabilized Zirconia in the CaO‐ZrO2 System

Abstract

Partially stabilized zirconia (PSZ) ceramics in the system CaO-ZrO₂ were characterized. The microstructure, as revealed by optical microscopy, consisted of grains of pure ZrO₂ 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 ZrO₂. 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 ZrO₂ 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.