Fatigue strength of notched specimen in nickel-base superalloy at elevated temperatures

Because of its excellent mechanical properties at elevated temperature, a nickel-base superalloy has been widely used in the aerospace industry and nuclear power plants. In this study, rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300 °C, 400 °C and 500 °C to investigate the notch sensitivity at the elevated temperatures. It was found that the fatigue limits of plain specimens were higher at the elevated temperatures than at room temperature, which might be due to the suppression of the crack initiation at the elevated temperatures, however, the resistance to crack growth became smaller at the elevated temperatures than at room temperature. Therefore, the fatigue strength of a notched specimen, in which a crack initiated easily owing to the stress concentration introduced, was lower at the elevated temperatures than at room temperature. Consequently, the fatigue strength reduction factor was larger at the elevated temperatures than at room temperature.