Dislocation evolution and redistribution during stress relaxation in single crystal AD730TM after prior plastic strain at 700 °C

Abstract

Understanding dislocation evolution during viscoplastic deformation is essential to accurately predict high-temperature superalloy behavior. While creep and monotonic deformation are well studied, the evolution of the dislocation substructures during stress relaxation, particularly following prior plastic straining, remains unclear. This study investigates a single crystal γ/γ' AD730^TM superalloy deformed at 700 °C, focusing on dislocation evolution and redistribution. Transmission electron microscopy reveals that stacking faults formed during plastic straining progressively disappear during relaxation, suggesting thermally activated mechanisms such as dislocation re-association and recovery. After re-association, perfect dislocations spread into the matrix, forming a homogeneous dislocation network. These microstructural evolutions are believed to underlie the macroscopic stress relaxation behavior, which exhibits two regimes in the Norton diagram: an initial high-stress exponent regime linked to rapid dislocation rearrangement, followed by a low-stress exponent regime associated with broader dislocation activity.