High-angle ganin boundaries are generally deemed necessary for superplasticity in metals. In polycrystalline materials theg rain boundary character must be described in terms of a probability distribution rather than by a single parameter, and little has been reported on the relationship between this distribution and fine-grain superplasticity. For aluminum alloys that exhibit continuous recrystallization the results of computer-aided electron backscatter diffraction analysis have shown that bimodal grain boundary disorintation distributions are present in as-processed material and persist during subseuent annealing. Such distributions may be simulated by computer methods based on a mode, of the microstructure which assumes that deformation banding occurs during deformation processing. High-angle boundaries (=>30 deg) develop in assoication with deformation banding while boundaries of lower disorientation (<30 deg )develop by dislocation reactioj within the bands. Improved understanding of the grain boundary types associated with various microstructural transformation mechanisms will aid the design of processes to produce superplastic microstructures.
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