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 recrys-tallization. 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 recrystalli-zation 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 υ' 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 recrystal-lization, growth of recrystallized nuclei into the matrix, and growth of recrystallized grains by swallowing up each other.