Influence of stress dwell location on the creep–fatigue behavior of notched nickel-based single-crystal superalloy specimens at 900 °C

Nickel-based single-crystal superalloys are widely employed in critical hot-section components of aero-engines and industrial gas turbines. In this study, high-temperature creep-fatigue interaction tests were conducted on notched specimens of a nickel-based single-crystal superalloy under different stress dwell locations, including baseline cycling without dwell (baseline), dwell at maximum stress (“max dwell”), and dwell at minimum stress (“min dwell”). The results demonstrate that the stress dwell location exerts a pronounced influence on the fatigue life and failure modes of notched specimens. Specifically, under baseline cycling and min dwell conditions, failure is dominated by the initiation and propagation of surface-initiated fatigue cracks. In contrast, under max dwell conditions, the fracture surfaces exhibit a mixed morphology characterized by the coexistence of quasi-cleavage facets and dimpled microvoid coalescence. A damage-coupled viscoplastic constitutive model was employed to simulate the cyclic response of notched specimens under different dwell conditions by finite element analysis, and the predictions indicate that the model can reasonably reproduce the crack initiation and evolution behavior over a range of stress dwell locations. On this basis, the classical Basquin fatigue life model was modified by incorporating stress triaxiality and damage evolution metrics, thereby establishing a life prediction methodology applicable to high-temperature notched creep-fatigue interaction, which captures the observed trends in life degradation with satisfactory accuracy.