An examination of the flow process in superplastic yttria-stabilized tetragonal zirconia

Extensive high temperature creep data are available for a superplastic yttria-stabilized tetragonal zirconia containing 3 mol% of Y2O3 (termed 3Y-TZP). These data are analyzed and it is shown that, contrary to superplastic metals, intragranular slip cannot occur to accommodate grain boundary sliding at the temperatures and stresses examined experimentally. It is proposed instead that how occurs by Coble diffusion creep controlled by movement of the Zr4+ ions and, because of the small grain sizes in the 3Y-TZP materials, the creep rates are reduced through interface-controlled diffusion creep. A detailed analysis demonstrates this approach predicts the experimental creep rates to within one order of magnitude over the range of grain sizes and temperatures examined experimentally and it accounts also for the reported values for the stress exponent and the exponent of the inverse grain size at high and low stress levels. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.