A threshold stress for the superplastic deformation in Y2O3-stabilized tetragonal ZrO2

The superplastic deformation behavior of Y2O3-stabilized tetragonal ZrO2 exhibits three stress regions in the stress-creep rate relationship. In the high and intermediate stress regions, the stress exponent n varies from ≈2.0 to ≥3.0 with decreasing stress. The origin of the increasing n-value can be explained from the existence of a threshold stress, σ0 that depends on the grain size. In the high and intermediate stress regions, the deformation behavior replotted by effective stress can be characterized by the straight relationship with n ≈ 2.0, suggesting that the deformation occurs through a single deformation mechanism of grain boundary sliding incorporated with the threshold stress.