Experimental investigation on recrystallization mechanism of a Ni-base single crystal superalloy

Experimentation by TEM, EBSD and optical microscope is used to understand recrystallization in a Ni-based single crystal superalloy. Hot compression is employed at different temperatures to provide driving force for recrystallization. Recrystallization sensitivity for this investigated alloy is provided. The results indicate that deformation temperature, as well as annealing conditions, has a great influence on recrystallization behavior. Samples deformed around 980 °C have the highest propensity for recrystallization, and stacking faults can facilitate the recrystallization process by themal twinning nucleation. Microstructural observation shows that as-cast inhomogeneity plays a significant role in the microstructure evolution, especially below γ′ phase solvus. Recrystallization nucleates first and grow rapidly in the dendritic arms. In the interdendritic regions, thermal twinning play the dominant role, and small grains remain after recrystallization is completed. Grain coarsening is rather difficult owing to abundant twinning grain boundaries. The eutectics in the IDRs can undergo recrystallization by themselves in the case of high plastic strains, and impede the grain boundaries at low plastic strains.