Creep, fatigue and creep-fatigue crack growth rates in parent and simulated HAZ type 321 stainless steel: Gladwin, D.N., Miller, D.A., Neate, G.J. and Priest, R.H.Fatigue Fract. Eng. Mater. Struct. 1988, 11, (5), 355–370

Abstract

Cyclic behavior of a nickel-based GH4169 superalloy under fully-reversed and asymmetric creep-fatigue tests with strain-controlled is investigated at 650℃. Significant tension–compression asymmetry and continuous cyclic softening are observed for all loading waveforms. The material exhibits mean stress relaxation under asymmetric loading and fully-reversed loading with valley strain dwells. Moreover, stress relaxation behavior during the dwell period is almost independent of the number of cycles. In order to identify the deformation mechanism, the evolutions of mean value and amplitude of the internal stress (back stress and effective stress) based on the partition of hysteresis loops are analyzed. Results show that both the cyclic softening and mean stress relaxation are primarily dominated by the evolution of back stress and secondarily affected by that of effective stress. Such findings lay a solid foundation for further investigations of reasonable cyclic deformation description and accurate life prediction in GH4169 alloy under creep-fatigue loadings.