EFFECT OF NIO DISSOLUTION ON THE MICROSTRUCTURAL DEVELOPMENT OF T'-ZRO2 WITH 5 MOL-PERCENT Y2O3

The ageing (1300-degrees-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-degrees-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.