Thermo-mechanical fatigue behavior and life prediction of selective laser melted inconel 718

The thermo-mechanical fatigue (TMF) property and corresponding damage mechanisms of selective laser melted (SLM) Inconel 718 superalloy were investigated systemically. The results show that the TMF life under in-phase (IP) loading is lower than that under out-of-phase (OP) loading, and the life difference gradually decreases with decreasing the strain amplitude. The fatigue cracks mainly exhibit inter-granular cracking characteristics under IP loading, and the δ phase embedded to the grain boundary promotes the creep cavity formation and then causes the fatigue crack propagation. While under OP loading, the fatigue crack is mainly characterized by trans-granular cracking, the oxidation induced crack extends from the specimen surface to the interior. A parameter, known as the shape factor k, has been discovered to exhibit high stability in temperature variations. Given the high stability of the k value and the quantitative relationship between stress and plastic strain range across different loading modes, a rapid prediction method for TMF hysteretic energy based on low cycle fatigue (LCF) has been proposed. Finally, combined with the energy cumulative damage model, the TMF life is successfully predicted. This approach significantly reduces the experimental quantity and complexity required for the TMF life prediction process, demonstrating substantial industrial application value.