Effects of CuO and Al2O3 additions on the tetragonal phase stability in 2.5 mol% Y-TZP ceramics

Yttria-coated zirconia powders were simultaneously doped with up to 0.05 wt% CuO and 0.08 wt% Al2O3 Prepared doped pellets were sintered at 1300 degrees C but at different ramp rates ranging from 5 - 100 degrees C/min. and soaking periods of I to 2 hours. It was found that the 10 degrees C/min. and 2 hours hold cycle gave the overall best mechanical properties. Nevertheless, all of the doped samples revealed excellent resistance to hydrothermal degradation in superheated water at 180 degrees C and 1 MPa regardless of the sintering conditions, developing less than 13% monoclinic phase content after 200 hours of exposure whereas the undoped ceramic failed catastrophically in the early stages of ageing. Possible ageing mechanisms are discussed and the enhanced ageing resistance of the Cu-doped Y-TZPs is in part attributed to the fine grain size of the sintered body resulting from the presence of a transient liquid phase during low temperature sintering.