Experimental evidence for diffusion creep in the superplastic 3 mol% yttria-stabilized tetragonal zirconia

Although there have been numerous studies on the high temperature deformati on characteristics of the superplastic 3 mol% yttria stabilized tetragonal zirconia (3YTZ). the rate controlling deformation mechanism has not been id entified unambiguously. In the present study, experiments were conducted on 3YTZ at high stresses and at coarser grain sizes than used conventionally for superplasticity. The experimental results reveal, for the first time. a n intragranular dislocation motion controlled high stress regime that is in dependent of the grain size. With a decrease in stress, there is a transiti on to a Newtonian viscous deformation regime consistent with Coble grain bo undary diffusion creep. Ar sufficiently low stresses. or in materials with finer grain sizes, there is a further transition to a grain size dependent interface controlled deformation regime. Analysis of the experimental data suggests strongly that superplastic flow in 3YTZ occurs by an interface con trolled deformation mechanism. (C) 2001 Acta Materialia Inc. Published by E lsevier Science Ltd. All rights reserved.