Tensile ductility behavior of superplastic ceramics

Abstract

The tensile elongation of fine-grained ceramics has been examined as function of flow stress and grain size. It is shown that tensile elongation is a strong function of flow stress increasing with decreasing flow stress, even though the values of strain-rate-sensitivity exponent remain high. The tensile ductility dependence on grain size was also investigated for many fine-grained ceramics either under a constant strain rate condition or a constant stress condition. It was found that large increase of tensile ductility with the decrease of grain size under a constant strain rate, is primarily attributed to the decrease in flow stress accompanying grain size refinement. When temperature is sufficiently high, however, superplastic ceramics show superplastic metallic-like behavior. This variation of tensile elongation behavior is attributed to the change in damage evolution mode from crack formation to cavity-stringer formation.