Colloidal processing and superplastic proprties of fine-grained zirconia-based ceramics

Colloidal processing was applied to obtain dense and homogeneous yttria-doped tetragonal zirconia (YTZ), alumina-dispersed YTZ, and magnesia- and titania-doped YTZ. Their slurries were prepared by adding appropriate amounts of polyelectrolyte, and their fine-grained bodies were obtained through slip casting, cold isostatic pressing and low-temperature sintering. The obtained bodies show excellent superplastic properties. In particular alumina addition was found to (1) decrease the limit temperature of superplasticity in YTZ to 1573 K or lower, (2) increase the limit strain rate for large elongation exceeding 300% up to 1.2×10^-2 s^-1 at 1573 K and (3) large tensile elongation exceeding 1000% at 1.7×10^-4 s^-1. The effects of microstructure such as grain size, grain-boundary structure and cavity density on the superplastic properties are discussed by comparison with the conventionally prepared samples. The creep parameters prepared by the colloidal processing were similar to those prepared by conventional dry processing. Their excellent superplasticities are due to the reduction of residual defects, fine-grained and homogeneous microstructures.