Fatigue strength of Inconel 718 at elevated temperatures

The strength of Inconel 718 under rotary bending fatigue is investigated at roam temperature, 300, 500 and 600 degrees C in air. It is found that in t he long-life region, the fatigue strength of a plain specimen is much highe r at elevated temperatures than at room temperature, though the static stre ngth decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early gr owth behaviour of a small crack. The results are discussed in relation to t he competition between the softening of the nickel matrix (gamma phase) and the surface oxidation at elevated temperatures.