Dislocation Model for Continuous Recrystallisation during Initial Stage of Superplastic Deformation

Abstract

According to dislocation models, grain boundary sliding (GBS) causes stress concentrations when the sliding is impeded. Relaxation of the stress concentrations can be done by the emission of dislocations from one grain boundary to another. This process could be limited by the rate at which the dislocations are emitted (source control), or traverses the grains (glide or lattice climb control), or are absorbed into the boundaries (grain boundary climb control). The rate at which the grains slide past each other can be controlled by (1) the removal of a pile-up of lattice, the emission of lattice dislocations from grain boundary ledges and by the removal of pile-ups of grain boundary dislocations. These models require the grains to have high angle mobile boundaries such that grain boundary sliding processes can occur and are then accommodated by dislocation movements. For some quasi-single phase aluminum alloys, at the initial stage of superplastic deformation most of grain boundaries have low angles. Since movement of these subgrain boundaries needs very high energy, grain boundary sliding becomes difficult. It is widely reported that continuous recrystallization mechanism dominates the initial stage of superplastic deformation in quasi-single phase aluminum alloys.