MICROMECHANICAL MODELING OF SUPERPLASTIC DEFORMATION

There is a definite need to model the deformation mechanisms in superplasticity as none of the existing models accurately describe its mechanical and microstructural features. In this paper, a micromechanical model of superplastic deformation is developed from the constituent grain level to the level of the polycrystalline bulk material in an explicit manner. This model considers accommodation mechanisms based on diffusional flow and dislocation movement and relates their strain rate to the macroscopic superplastic strain rate by way of parameters determined from experimental data. It computes the strain fields of individual grains depending on their crystallographic orientation and the micromechanical deformation mechanisms. The resulting stress redistribution among the grains is accounted for by the self-consistent relation. The model is applied to statically recrystallized 7475 aluminum alloy and dynamically recrystallizing 2090-OE16 aluminum-lithium alloy and the influence of temperature and grain size on the flow stress vs strain rate behavior are successfully predicted.