EFFECTS OF SOLUTE ION AND GRAIN-SIZE ON SUPERPLASTICITY OF ZRO2 POLYCRYSTALS

The deformation of ZrO2 polycrystals containing 2 to 8 mol % Y2O3 or 12 mol % CeO2 were investigated by uniaxial tension and tensile creep tests at elevated temperatures. It was found that there were two deformation mechanisms. The stress exponent was close to 2 for the fine-grained materials (less than 1-mu-m), but the exponent decreased with increasing grain size. This behaviour was analysed using a model based on grain-boundary sliding with diffusion accomodation, in which the diffusion creep controlled by interface-reaction and that controlled by diffusion of cations were incorporated. The diffusion coefficient of cations was greatly affected by the concentration of the solute ions. It was observed that there was a negative correlation between interface-reaction rate and Y2O3 concentration.