Flow processes in superplastic yttria-stabilized zirconia: A Deformation Limit Diagram

The possible rate-controlling mechanisms in the deformation of superplastic 3Y-TZP are considered. It is generally recognized that intragranular dislocations play only a limited role in the creep of this material at stresses below ∼100 MPa when testing at temperatures in the range from 1573 to 1873 K. Therefore, a single rate-controlling mechanism is proposed which is consistent with experimental reports of a single activation energy. The proposed mechanism is based on Coble diffusion creep with a transition to interface-controlled diffusion creep at the lowest stress levels. It is shown that an equation derived on the basis of this mechanism provides a very good fit, to within an order of magnitude of the strain rate, for experimental data reported by different investigators. A Deformation Limit Diagram is introduced and constructed to provide a simple pictorial representation of the transitions occurring in the creep behavior at these low stresses.