Effect of Overheating Events on Microstructure and Low-Cycle Fatigue Properties of a Nickel-Based Single-Crystal Superalloy

Micro-mechanical response to overheating events is an important factor when considering the serviceable life of aero-engine components. A key lifing consideration is the low-cycle fatigue (LCF) behavior of nickel-based single-crystal superalloy components. In this study, the LCF response was investigated at different overheating temperatures (1100 to 1300 °C) and times (30 to 120 min). The overheating events had an impact on the γ' phase content, which was observed to decrease with the increase in overheating temperature and time (fully dissolving at 1300 °C). Due to the dissolution of γ' precipitates, the average γ' size was shifted to larger values, however, the subsequent cooling post the overheating events resulted in the formation of tertiary γ' and a bimodal particle distribution. During the LCF tests, that were performed after the overheating exposure, either cyclic hardening or softening was observed. It could be concluded that overheating exposures had no significant effect on the fracture features. However, overheating events resulted in a decrease of LCF properties, which was correlated to the local dislocation response.