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

Abstract

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, microstructural evolution, and dislocation distribution in pre-deformed Ni-based SX superalloys. Through indentation-induced deformation and subsequent SRA treatments (1150–1250°C for 5–20 h) followed by solution heat treatment (SHT), the RX behavior, geometrically necessary dislocation (GND) density, and γ′ phase evolution were systematically analyzed. The results demonstrate that SRA pretreatment reduces GND density in deformation zones by 35.90% to 54.20%, however, it does not completely prevent the occurrence of RX. At SRA temperatures below 1200°C, cellular RX occurs, while equiaxed RX emerges at 1250°C due to γ′ phase dissolution and enhanced thermal activation. Prolonged SRA time and elevated temperatures initially reduce deformation stress by promoting dislocation annihilation and γ′ phase coarsening. However, excessive temperatures (>1200°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.