Study on low-frequency fatigue performance of HT700P nickel–iron based high-temperature alloy

In this study, the low cycle fatigue properties of a new nickel–iron-based superalloy HT700P at different strain amplitudes at 650℃ and 700℃ were investigated. The results show that at 650℃, with strain amplitudes of 0.3% and 0.7%, the fatigue life of the samples was 17,007 cycles (14 h) and 580 cycles (1.13 h), respectively. At 700℃, the fatigue life was 13,966 cycles (11.65 h) and 469 cycles (0.91 h) for the same strain amplitudes.When the total strain amplitude is 0.3%, the alloy exhibits the behaviour of cyclic softening first, then cyclic hardening and finally cyclic softening. When the total strain amplitude is 0.7%, the alloy exhibits cyclic softening behaviour as a whole. Cyclic softening is related to the continuous cutting of the γ′ phase by dislocations and the coarsening of the γ′ phase, whereas cyclic hardening is caused by the interaction between dislocations and precipitated phases. By analyzing the fatigue fracture morphology, it can be seen that the fatigue cracks sprouted from the surface of the specimen; when the temperature was 650℃ and the total strain amplitude was 0.3% and 0.7%, the fracture morphology of the samples was mainly characterized by the fatigue glow and extended inwardly in the mode of transgranular mode. The microscopic mechanism of low-week fatigue in HT700P high-temperature alloy is plane slip.