MICROMECHANICAL MODELING OF SUPERPLASTIC DEFORMATION

There is a definite need to model the deformation mechanisms in superp lasticity as none of the existing models accurately describe its mecha nical and microstructural features. In this paper, a micromechanical m odel of superplastic deformation is developed from the constituent gra in level to the level of the polycrystalline bulk material in an expli cit manner. This model considers accommodation mechanisms based on dif fusional flow and dislocation movement and relates their strain rate t o the macroscopic superplastic strain rate by way of parameters determ ined from experimental data. It computes the strain fields of individu al grains depending on their crystallographic orientation and the micr omechanical deformation mechanisms. The resulting stress redistributio n among the grains is accounted for by the self-consistent relation. T he model is applied to statically recrystallized 7475 aluminum alloy a nd dynamically recrystallizing 2090-OE16 aluminum-lithium alloy and th e influence of temperature and grain size on the flow stress vs strain rate behavior are successfully predicted.