Recrystallization of Ni base superalloy DZ4

The recrystallizations behavior of shot peening samples of Ni base superalloy DZ4 both at lower temperature in the γ + γ′ field as well as during solution treatment were studied by SEM and XRD. The results show that the shot peening layer starts recrystallizing at 1000°C for 2 h. When the alloy was treated at the temperature lower than that of γ′ phase dissolved completely, the cellular recrystallization was observed, and recrystallization occurred through the growth of recrystallized grain when the alloy was treated at solution temperature. The γ′ phase can retard the migration of recrystallizing grain boundary. The heat treat temperature has more influence on recrystallization rate and layer thickness than the holding time. By metallographic examination of the tensile samples at 1220°C for 2 h, the recrystallized grains already formed after a small plastic deformation of about 0.9%. Recrystallized grains always nucleated preferably at the surface of tensile samples.