Post-dynamic recrystallization in a Ni-based Waspaloy under non-isothermal sub-solvus thermomechanical processing

This study investigates the post-dynamic recrystallization (PDRX) behavior of the nickel-based superalloy Waspaloy under sub-solvus conditions. We demonstrate that the conventional direct heating deformation method significantly underestimates the material's microstructural evolution potential, as it fails to replicate the cooling history of actual industrial hot forming processes. To address this, two thermomechanical paths were designed: direct heating deformation and an innovative step-cooling deformation. Remarkably, the step-cooling path promoted extensive PDRX, yielding a uniform fine-grained microstructure. In contrast, PDRX was strongly suppressed in the direct heating specimens. Microstructural analysis indicates that during direct heating, dynamic recrystallization dissolves γ′ precipitates within recrystallized grains, creating a heterogeneous structure where γ′-rich deformed grains exerted a strong pinning force that halted further PDRX. The step-cooling path, by maintaining a ∼50 °C window between γ′ precipitation and dissolution, enabled rapid PDRX in a γ′-free matrix. This work highlights that accurately replicating the industrial thermal history is critical for evaluating the microstructure evolution of phase-transforming superalloys. The step-cooling method provides a more scientifically valid approach compared to conventional direct heating.