Cyclic transient creep behavior and modeling of nickel-based superalloy under creep–fatigue loading conditions

Abstract

The present experimental work revealed that under fully reversed creep–fatigue loading conditions ($R=-1$), the material exhibits a recurring cyclic transient creep phase, never entering the steady-state creep regime. The cyclic creep process is dominated by primary creep, with the creep rate during the transient phase being 1–2 orders of magnitude higher than that of steady-state creep. As the loading ratio increases to $R=-0.5$ and $R=0$, the prominence of these transient effects decreases; the creep rates converge toward steady-state values as reverse plastic deformation diminishes. This behavioral trend suggests that fatigue-induced reverse plastic deformation is the primary mechanism for regenerating transient creep behavior in the material. Based on these observations, an empirical constitutive model was developed to characterize the cyclic transient creep features and quantify the acceleration effect of material creep softening. The model highlights the critical need to incorporate transient creep effects into life prediction frameworks. Failure to account for these effects could lead to non-conservative estimations of component service life.