Doping amount and temperature dependence of superplastic flow in tetragonal ZrO2 polycrystal doped with TiO2 and/or GeO2

The doping amount and temperature dependence of superplastic flow in a TiO2- and/or GeO2-doped tetragonal ZrO2 polycrystal (TZP) were investigated in the doping range of 0.2-8 mol.% and in the temperature range of 1200-1550 °C. While the tensile ductility in the TZP is significantly improved by the co-doping of TiO2 and GeO2, there is an optimum combination of doping amount and temperature for enhancing the tensile ductility. The present study also shows that the flow stress decreases with an increase in the doping amount, but this decrease levels off with a 2-3 mol.% addition of GeO2 or (TiO2-GeO2). The data for the flow behavior and thermal groove experiment indicated that TiO2 and/or GeO2 doping enhances the grain boundary diffusion of zirconium cations and reduces the grain boundary energy, respectively. These effects of grain boundary segregation can be regarded as the cause of the improved high-temperature ductility of (TiO2-GeO2)-doped TZP.