Effect of NiO dissolution on the microstructural development of t′-ZrO2 with 5 mol% Y2O3

Abstract

The ageing (1300 °C for 1–300 h) dependence of the microstructure of the metastable tetragonal (t′-) ZrO2 (plasma-sprayed Y-PSZ with 5 mol% Y2O3) in the sintered (1300 °C, 5 h) t′-ZrO2/NiO (10 mol%) composite was studied by transmission electron microscopy. Short-term (10 h) ageing caused incomplete decomposition of t′-ZrO2 into tweed assemblages containing t′-ZrO2 relics and tetragonal (t-) ZrO2 precipitates in the cubic (c-) ZrO2 matrix. The t′-ZrO2 relics retained anti-phase domain boundary (APB) and primary deformation twins, but no secondary deformation twins. Further ageing (e.g. up to 100 or 300 h) caused growth of the twin variants of t-ZrO2 with {101} habit plane. The large t-ZrO2 variants transformed directly into m-ZrO2 twins, but not into t-ZrO2 colonies. In addition to the relics in the aged samples, t′-ZrO2 with APB may also form locally from a solute-redistributed c-ZrO2 by slow cooling.