Flow behavior and dynamic recrystallization of hot isostatically pressed EP741NP superalloy

Flow behavior and dynamic recrystallization of the hot isostatically pressed superalloy EP741NP has been investigated. The isothermal compression tests at a moderate strain rate of 0.01 s⁻¹ and sub-solvus temperatures are performed on the thermomechanical simulator. The deformed samples are analyzed by scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. The hot isostatically pressed EP741NP alloy exhibits abnormal flow behavior with four work hardening stages when deformed below 1140 °C. Due to the preferential local strain around the previous particle boundary, the primary γʹ interacts with dislocations, stimulating local recrystallization and causing abnormal yielding during work hardening. Subsequently, the secondary γʹ phases dissolve with the advancing recrystallization front, releasing the dislocations pinned by γʹ and forming γ nuclei. However, the high solute concentration in the recrystallization front restricts the growth of new γ grains. The dissolved secondary γʹ discontinuously re-precipitates on new γ grain boundaries, forming a special γ + γʹ structure.