Recrystallisation nucleation of nickel base single crystal superalloy under compression

Recrystallisation nucleation of a nickel base single crystal superalloy cold deformed by compression and annealed at various temperatures has been investigated. The specimens were compressed using universal testing machine under an initial strain rate of 5x10(-4) s(-1) at room temperature. Annealing temperatures were chosen from 1100 to 1300 degrees C. The microstructure changes of the deformed and annealed samples were observed by optical microscopy, SEM with electron backscatter diffraction and TEM. It has been found that the surface and dendritic core are the preferential nucleation sites of recrystallised nucleus. The surface may lead to dislocation loss and relaxation of long range stresses, which will induce the recrystallised grains. At the dendritic core, rapid dissolution of gamma' particles during annealing reduces the resistance of grain boundary migration. Nucleation by low angle boundary migration and bow was confirmed during the recrystallisation of nickel base single crystal superalloy.