Evaluation of fatigue crack growth rate and life prediction of Inconel 718 at room and elevated temperatures

The fatigue crack growth behavior of Inconel 718 was investigated under rotating bending fatigue at room temperature, 300, 500, and 600°C in air. It has been found that the small crack growth rate could be evaluated by the small crack growth law at high stress levels, where the small-scale yielding conditions are exceeded and the Paris law is not applicable, irrespective of the temperature. The fatigue strength of plain specimens increased considerably in the long-life region at the elevated temperatures, because the early growth of a small crack in the range of 20-30 μm was suppressed. However, a crack grew faster at higher temperature after growing beyond about 50 μm due to the decrease of crack growth resistance. The fatigue life in the stable crack growth period can be predicted by the small crack growth law.