Superplasticity in Ceramics: Accommodation‐Controlling Mechanisms Revisited

High temperature plasticity in yttria stabilised tetragonal zirconia polycrystals (Y-TZP)

“…The modified model’s prediction of the creep laws as a function of kink density are presented in a simplified form in Table 1. 81 As can be observed, the creep laws are similar to the Coble model, with the rate controlling processes being the diffusion in the liquid phase or in the adsorption layer.…”

“…This is the central picture of the so called solution precipitation model, developed by Raj and Chyung 79 and subsequently modified. 75,80,81 In the modified model, 75,81 it is assumed that solution and precipitation take place at steps (kinks) formed at the grain boundaries. The solution precipitation process involves the movement of these kinks, and the strain rate is therefore related to the kink velocity and density.…”

Recent Insights on the Superplastic Behaviour of Ceramics

“…According to the values of the interfacial energy for different ceramics, this threshold stress is too small and it can be neglected in many systems. If it exists as in the case of yttria tetragonal zirconia polycrystals, the numerical value is far too high to be explained through a change in the interfacial energy during grain sliding [2,3]. In this case, the yttrium segregated to the grain boundaries is at the origin of the threshold stress.…”

“…Since its discovery in 1986 by Wakai [1], superplasticity in ceramics has deserved considerable attention due to its potential industrial applications, such as superplastic forming at moderate temperatures and superplastic joining. From a scientific viewpoint superplasticity in ceramic materials is still a challenging task: despite the large number of papers reporting such phenomenon in diverse monolithic ceramics and ceramic composites, its origin from fundamental basis is not still clarified [2,3]. This is particularly disappointing in the case of yttria tetragonal zirconia-based ceramics, the first superplastic ceramic material reported in literature and still a model-system to test the validity of the different proposed models described in literature.…”

“…This is particularly disappointing in the case of yttria tetragonal zirconia-based ceramics, the first superplastic ceramic material reported in literature and still a model-system to test the validity of the different proposed models described in literature. A good summary of the different approaches for the scientific comprehension of superplasticity is provided in [3,4]. In general all of them can be classified into two different groups: 1-Models invoking dislocation activity as the driving force for superplasticity in ceramics.…”