Low-Cycle Creep-Fatigue Behavior and Life Prediction of GH3535 Superalloy for Molten Salt Reactor at 700°C

The low-cycle fatigue (LCF) and creep-fatigue interaction (CFI) behavior of GH3535 superalloy was systematically investigated at 700°C. The LCF tests were conducted using a sine wave with strain amplitudes ranging from 0.2% to 0.5%, while the CFI tests were performed under various strain amplitudes and tensile hold time. Experimental results indicated that the life cycles of GH3535 superalloy decreased with the increasing strain amplitude and hold time. The fracture mechanisms of the material revealed that the increase in strain amplitude led to increasing number of crack initiation sites during LCF tests. In the CFI regime, the cyclic process exhibits significant stress relaxation during the tensile hold time, with the magnitude of the maximum initial relaxation stress being related to the hold time. The increasing hold time in CFI tests accelerated crack propagation, with the propagation mode changing into a mixed intergranular-transgranular pathway. The creep-fatigue life was predicted using both classical models and energy-based models that consider oxidation damage. An improved creep-fatigue-oxidation life prediction model based on the Linear Cumulative Damage (LDS) rule was proposed by incorporating an oxidation influence factor and modifying the stress relaxation. The predicted CFI life of the modified model shows good consistency with the experimental results, with most data points located within a 1.5-fold error band.