Effect of high-temperature stress relief annealing on the recrystallization of pre-deformed Ni-based single crystal superalloy

Recrystallization (RX) is a grain defect caused by stress concentration in single-crystal (SX) superalloys. This study investigates the effects of high-temperature stress relief annealing (SRA) on the inhibition of RX, micro-structural evolution, and dislocation distribution in pre-deformed Ni-based SX superalloys. Through indentation-induced deformation and subsequent SRA treatments (1150-1250 degrees C for 5-20 h) followed by solution heat treatment (SHT), the RX behavior, geometrically necessary dislocation (GND) density, and gamma ' phase evolution were systematically analyzed. The results demonstrate that SRA pretreatment reduces GND density in deformation zones by 35.90-54.20 %, however, it does not completely prevent the occurrence of RX. At SRA temperatures below 1200 degrees C, cellular RX occurs, while equiaxed RX emerges at 1250 degrees C due to gamma ' phase dissolution and enhanced thermal activation. Prolonged SRA time and elevated temperatures initially reduce deformation stress by promoting dislocation annihilation and gamma ' phase coarsening. However, excessive temperatures (>1200 degrees C) accelerate the formation of subgrain boundaries, triggering RX. This study reveals a critical relationship between dislocation recovery and RX behavior, providing insights into optimizing SRA parameters to mitigate RX defects in the manufacturing of SX turbine blades.