High-temperature deformation of Ni-based superalloy and recrystallization prevention by recovery

Achieving high recoverability is essential to maintaining the structural integrity for Ni-based superalloy single crystals. However, the recovery and recrystallization mechanisms in Ni-based superalloys after high-temperature deformation are still discussed controversially. This study reveals that for plastic strains of up to 3.2 %, dislocations carry plasticity in superalloy single crystals compressed at high temperatures, and that both dislocations as well as superlattice stacking faults can be easily annealed out by recovery treatment to preempt recrystallization. This means that the recoverability of Ni-based superalloy single crystals can be increased by more than twice compared to previous reports. For larger plastic strains, deformation twins form. They block moving dislocations which assemble in new boundaries that eventually trigger dynamic recrystallization. Upon subsequent heat treatment, such newly recrystallized grains grow rapidly further, resulting in a coarse polycrystalline microstructure. Consequently, avoiding deformation twins becomes the key to maintaining the single-crystalline microstructure.