GRAIN-SIZE EFFECT IN HIGH-TEMPERATURE CREEP AND SUPERPLASTIC DEFORMATION OF POLYCRYSTALLINE MATERIALS

A model is presented in this paper for high temperature creep of polycrystalline materials. Two deformation modes are considered in the model, namely diffusional flow and power-law creep. The grain size distribution is also taken into account to describe the overall steady-state creep deformation properties. A critical grain size, D-c, is defined in the grain size distribution, which is determined by such factors as applied stress, test temperature, and the material properties (diffusion coefficient, shear modulus, melting temperature, etc). At certain temperature and applied stress, grains with size smaller than D-c will deform by diffusional flow, and grains with size larger than D-c will deform by power-law creep. This model predicts that within certain steady-state creep rate ranges, a polycrystalline material will undergo superplastic deformation.