Low-Cycle-Fatigue Life Variation According To Temperature In Directionally Solidified Ni-Base Superalloy

The high-temperature parts of a gas-turbine engine eventually fail, due to the accumulated damage caused by the thermal and mechanical cyclic stresses during start-up and shut-down. To prevent such failures, methods for predicting the engine life under various damage mechanisms0 have been studied. In this paper, an experimental study on low-cycle-fatigue (LCF) life assessment was carried out at elevated temperatures. The results showed that the LCF life is on the order of 800>650>950 degrees C. This tendency was consistent with that of the yield-strength variation with temperature. The plastic strain in the tensile behavior was the lowest at 800 degrees C. Thus, it was confirmed that the plastic strain affected the LCF life. Fracture-surface and microstructural observations did not exhibit characteristics that could explain the LCF life tendency with temperature. In the future, additional analyses will be conducted to find the metallurgical factors affecting LCF life.