Effect of small amount of alumina doping on superplastic behavior of tetragonal zirconia

The effect of Al2O3 doping of around 0.1 wt % on superplastic behavior was studied in 3 mol % yttria-stabilized tetragonal zirconia polycrystal (TZP) which was free from SiO2 contamination and had a grain size of 0.4 mu m. Compression creep tests revealed that high-purity TZP with less than 0.07 wt % Al2O3 had two deformation regions: the low stress region had a stress exponent of three and an apparent activation energy of 640 kJ/mol, and the high stress region had two and 460 kJ/mol. On the other hand, TZP containing more than 0.12 wt % Al2O3 had only one region which had a stress exponent of two and an activation energy of 480 kJ/mol. The region of diffusion control with a stress exponent of one was not observed in any samples. High resolution transmission electron microscopy revealed that no amorphous grain boundary phase was produced even with 0.18 wt % Al2O3 doping. Energy dispersive X-ray spectroscopy near grain boundaries revealed that yttrium was segregating at the grain boundaries with denuded zones of 30 nm width, which were created during slow cooling from the sintering temperature. (C) 1999 Kluwer Academic Publishers.