High-temperature Creep Resistance in Rare-earth-doped, Fine-grained Al₂O₃

High-temperature creep in undoped Al₂O₃ and La₂O₃- or Y₂O₃- or Lu₂O₃-doped Al₂O₃ with a grain size of about 1 µm is examined in uniaxial compression testing at temperatures between 1150 and 1350 °C. The high-temperature creep resistance in Al₂O₃ is highly improved by the rare-earth oxide doping in the level of 0.045 mol %, and the creep rate is suppressed in the order La₂O₃ <Y₂O₃ <Lu₂O₃. Rare-earth ions in each doped Al₂O₃ are found to segregate in Al₂O₃ grain boundaries without forming amorphous phase or second-phase particles. The activation energy for creep in undoped Al₂O₃ is estimated to be 410 kJ/mol, while it is about 800 kJ/mol in the three rare-earth oxide-doped Al₂O₃. The grain boundary diffusivity must be highly reduced by the segregation of the dopant cation in Al₂O₃ grain boundaries.