A micromechanistic model of superplastic behavior in pseudo single phase aluminum alloys

Abstract

Grain boundary sliding (GBS) has been shown to account for essentially all the deformation under optimum superplastic conditions. It is also recognized that GBS is accommodated by diffusional and dislocation mechanisms active within the grains and their boundaries. Most of the existing models for superplasticity relate the strain rate of the accommodation processes of GBS to the macroscopically measured strain rate. The author conform to this approach and present a micromechanics-based deformation model which considers accommodation due to diffusional flow and dislocation movement at the grain level. The model derives the superplastic strain of the aggregate from the level of its constituent grains. It uses the self-consistent method to evaluate the grain to grain variation of stress during superplastic deformation. The crystallographic structure of the material and the corresponding slip systems are used in modeling the deformation in a grain. This model is developed in a manner similar to Murali and Weng`s unified theory of creep and strain-rate sensitivity of polycrystals. It is used to predict the influence of temperature on the flow stress vs. strain rate behavior of superplastic materials.