Characterization of the substructure around grain boundaries in a hot-deformed Ni-30%Fe austenite model alloy

Abstract

The nucleation of recrystallization is determined by the properties of the underlying subgrains: namely, subgrain size and misorientation. Under defined conditions, recrystallization nucleation occurs at the boundaries between deformed grains, and their junctions. Nevertheless, previous characterization studies have dedicated no specific attention to the subgrains located around deformed grain boundaries. In this view, the substructure at such locations is here characterized for a hot-deformed Ni-30%Fe austenite alloy, employing electron backscatter diffraction. Firstly, results show that the boundary length fraction not surrounded by subgrains decreases with higher dislocation density around the boundary. Higher boundary dislocation density also results in smaller subgrain sizes and higher subgrain misorientations. The subgrain size reduction is appropriately described by a Staker-Holt-type relationship. This is the case despite the spatial gradient and relatively high values of the dislocation densities surrounding the deformed grain boundaries. To describe the increase in subgrain misorientation, a novel equation is proposed, showing good agreement with experimental data. Apart from this, subgrains neighboring triple grain junctions exhibit higher misorientations than those located around the boundaries, away from the junctions. This explains the preferential recrystallization nucleation at triple-junction sites. Finally, unlike suggested in literature, twin boundaries accumulate lower dislocation densities than general high-angle boundaries. This explains their lower recrystallization nucleation efficiencies. Nevertheless, for equal boundary dislocation density, the substructure developed around both boundary types does not differ significantly.