Constitutive equation for superplastic flow of fine-grained yttria-stabilized zirconia polycrystals

Available data of fine-grained yttria-stabilized zirconia polycrystals have been analyzed at different temperatures as a function of the stress, grain size and purity. It is demonstrated that a grain boundary sliding process with a threshold stress dependent on grain size and material purity accounts for the observed variations in the apparent values of the creep parameters n, p and Q. Accordingly, a constitutive equation has been developed, which is identical to the phenomenological relationship found for superplastic metallic systems when grain boundary sliding is lattice diffusion-controlled.