Effect of grain size on superplastic behavior of Y-TZP

Abstract

This paper reports that grain size strongly influences the properties of fine-grained superplastic metal alloys. In principle, fine grain sizes enhance grain boundary sliding which is the dominant superplastic deformation mechanism. Recently, some fine-grained ceramics have been shown to be superplastic in tension. A maximum tensile elongation of about 800% has been recorded in a yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). During superplastic deformation, concurrent grain growth, and in particular dynamic grain growth, was observed in this material. It has been demonstrated that this concurrent grain growth strongly affects the superplastic flow stress in the material, and also confuses the accurate determination of the stress dependency of the superplastic strain rate. It is important, therefore, to understand the precise grain size dependence of superplastic flow in ceramics. It has been shown that the superplastic strain rate of Y-TZP is inversely proportional to the grain size raised to a 1.8 power. The effect of concurrent grain growth, however, was not considered in their analyses.