Analysis of the fully-reversed creep-fatigue behavior with tensile-dwell periods of superalloy DZ445 at 900 °C.

• Fatigue life with dwell time is explained by mechanical response and damage mechanism. • Inelastic strain range, stress relaxation, mean stress, and hysteresis loop with dwell time. • Schematic illustration of fracture and deformation mechanism with dwell time. • Energy-life prediction model for the creep-fatigue data with high strain range. High total strain-controlled creep-fatigue tests of 1.8% were performed for a directionally-solidified Ni-based superalloy, DZ445, at 900 °C in air. Dwell times of 0, 2, and 5 min. were introduced at the tensile peak strain for each cycle. Experimental results show a decrease in fatigue life with increasing dwell time. The significant cyclic softening is observed after the application of the dwell time. The mean compressive stress and large plastic-strain accumulation are produced due to the stress relaxation in the tensile-dwell period, resulting in the increase of the hysteresis loop area. The typical single-source crack-initiation and transgranular crack-propagation are transformed into multi-source crack-initiation and mixed transgranular and intergranular crack-propagation mode by these characteristics. Dislocation features are transformed from cutting of γ' precipitates by multiple stacking faults to the mixed mode of dislocation climbing and slipping. The reduction in the fatigue life with increasing the dwell time is well explained on the basis of the mechanical response and damage mechanism. The fatigue life is also predicted by the energy-based life-prediction model. [ABSTRACT FROM AUTHOR]