The Influence of Titania on Creep in Superplastic Zirconia

Detailed high-temperature compression creep experiments on a pure 3 mol% yttria-stabilized tetragonal zirconia (3YTZ) and 3YTZ doped with 4.8 wt% TiO2 revealed that both materials exhibit a similar transition in stress exponents from n similar to 1 to n similar to 2 with a decrease in stress. The stress exponent of 1 and the inverse grain size dependence p of similar to 3 are consistent with the Coble diffusion creep at high stresses; the increase in stress exponent at low stresses is attributed to an interface-controlled diffusion creep process. Measurements revealed that grain-boundary sliding contributes to >similar to 50% of the total strain in both regions with n similar to 1 and n similar to 2, indicating the operation of the same fundamental deformation process in both regions. The creep data indicate that doping with TiO2 leads to an increase in the grain-boundary diffusion coefficients. The increase observed in the dihedral angle with doping is also consistent with the increase in grain boundary diffusion coefficient and the reported enhanced ductility in such materials.