Comparison of the creep-fatigue cyclic life saturation effect for three different superalloys

Abstract

This investigation reports the results of the strain-controlled creep-fatigue behavior of precipitation-strengthened directionally-solidified Nickel-based superalloy DZ445. The results refer to the processes performed at 850 °C in the total strain range of 1.0% with 0, 3, 10, and 30 min tensile-dwell time. It was found that, compared to cyclic life that decreases rapidly after the initial application of dwell time, the reduced cyclic life slows down gradually when the dwell time exceed 30 min (i.e., the “generalized saturation effect”). As the publicly reported creep-fatigue results of the solid-solution-strengthened superalloy Haynes 230 and Alloy 617 under the same loading conditions, the cyclic life continues to decrease even 30 min dwell time is reached, which is hard to reach the case of Nf saturation. The reasons to reach the cyclic life (Nf) saturation are systematically elaborated from two aspects, namely, mechanical response (maximum stress, plastic strain, hysteresis loop, stress relaxation, etc.), and damage mechanism (cracks, voids, dislocation structures, etc.). This research provides theoretical guidelines for achieving the safety design of the superalloy components in the creep-fatigue deformation.