Recrystallization of SRR99 single-crystal superalloy: Kinetics and microstructural evolution

As-cast SRR99 specimens were shot-peened and then annealed at 1250 and 1300°C for different times to investigate the kinetics of recrystallization. It was found that the relationship between annealing time and volume fraction of recrystallized grains could be described by the Johnson-Mehl-Avrami equation. Based on the kinetics analysis of the recrystallization process, the apparent activation energy for recrystallization was determined. In addition, the microstructural evolution during the recrystallization process at 1300°C was studied. Inwards, recrystallization first occurs in the dendritic core regions at the shot-peened surface. With the dissolution of coarse γ’ particles in the interdendritic regions, the recrystallized grain boundaries move through the interdendritic regions. Finally, the fully developed grains nearly have a uniform depth. The recrystallization process at the shot-peened surface is similar to that of wrought materials, which includes nucleation of recrystallization, growth of recrystallized nuclei into the matrix, and growth of recrystallized grains by swallowing up each other.