A unified dislocation density-based model for an aged polycrystalline Ni-based superalloy considering the coupled effects of complicate deformation mechanisms and initial δ phase

The flow characteristics and microstructure evolution of an aged nickel-based superalloy are researched by thermal compression experiments at different temperatures (1223-1283 K) and strain rates (0.001-0.1 s(-1)). Based on the theoretical analysis, the dynamic recrystallization kinetics and the evolution of grain size are quantitatively modeled. A unified dislocation density-based model is developed to characterize the flow features of the researched superalloy. In the developed model, the work hardening effect is taken into account by involving the coupled effects between the dislocations and substructures/grain boundaries/delta phases. Especially, the initial contents/morphologies of delta phase are reasonably considered. The dynamic softening mechanisms including dynamic recrystallization and dynamic recovery are considered. The comparisons between the predicted and experimental data indicate that the developed unified model can make accurate predictions for the flow stresses of the aged nickel-based superalloy at constant or variable strain rates. Also, it is found that the morphology of delta phase gradually transforms from spherical to short-rod-like or needle-like with the increased aging time. The dissolution and bend of delta phase induced by dislocation movement easily occur. Besides, the DRX behavior is accelerated, and the grains are refined as the aging time is increased.