Recrystallization in a Ni-based single-crystal superalloy traced by quasi-in-situ EBSD

Abstract

By using quasi-in-situ EBSD, we successfully probed the nucleation and growth of recrystallized grains during sub-solvus annealing at 1300 °C of an as-cast single-crystal superalloy after pre-compression. It clearly indicated that recrystallization nucleated in the interdendritic region through low-angle grain boundary migration under the experimental condition rather than subgrain coalescence or thermal twinning. Despite being hindered by the undissolved γ′ precipitates in the interdendritic region, these newly formed high-angle grain boundaries could still migrate rapidly. However, the migration velocity will slow quickly as the stored energy decreases. During 10.0-min annealing, the grain boundaries could migrate 14.4–27.4 μm, but the recrystallized grains were still confined in the interdendritic region without abnormal growth. These results provide novel perspective on the comprehension of recrystallization nucleation in single-crystal superalloys and the migration of newly formed high-angle grain boundaries under the hinderance of γ′ precipitates, and are valuable for developing process to control recrystallization.