Microtexture and grain boundary evolution during microstructural refinement processes in SUPRAL 2004

Abstract

Electron backscatter pattern (EBSP) analysis of as-processed, processed and annealed, and superplastically deformed specimens of commercially processed SUPRAL 2004 material has been employed to reveal the boundary misorientation distribution and evolution. Earlier studies using X-ray diffraction (XRD) and transmission electron microscopy on this alloy have attributed the transition to microstructures capable of supporting extensive superplastic flow to continuous recrystallization occurring early in the deformation process. The micro- and mesotextural data of the present study show that the deformation texture evident in the as-processed material persists without the formation of recrystallization texture components and remains up to the apparent onset of the grain boundary sliding (GBS) regime. Comparison of the correlated and uncorrelated boundary misorientation data illustrates that the development of boundaries misoriented by ∼5 to 15 deg is not random in nature. There is no evidence of recrystallization involving the formation and migration of high-angle boundaries during the refinement process. Microtextural and boundary data from this study provide evidence that the microstructural transition enabling superplastic mechanical behavior of SUPRAL 2004 may be described by a recovery-dominated, continuous process involving the development of moderately misoriented boundaries and leading to a refined microstructure with a boundary distribution of low interfacial energy character.