Superplastic flow in nanocrystalline and sub-microcrystalline yttria-stabilized tetragonal zirconia

Tensile deformation of nanocrystalline ZrO2 + 5 mol% Y2O3 at temperatures in the range of 1283-1403 K is described. It is demonstrated (a) that steady state flow is possible at temperatures of the order of 0.42 T-m, where T-m is the absolute melting point, (b) that 70% engineering strain could be obtained at 1403 K (0.46 T-m), and (c) that significant grain boundary sliding was present during deformation. Static and dynamic grain growth as also a decrease in the relative density of the specimen with deformation could be observed. The present results as well as those of Owen and Chokshi concerning superplastic flow in sub-microcrystalline materials taken from literature could be accounted for quantitatively using the grain boundary sliding controlled flow model of Padmanabhan and Schlipf, originally proposed for microcrystalline superplastic alloys. (C) 2001 Kluwer Academic Publishers.