Initiation and growth behavior of a small fatigue crack in nickel-base superalloy at elevated temperatures

摘要

Rotating bending fatigue tests were performed for nickel-base superalloy Inconel 718 at room temperature, 300 deg C, 500 deg C, and 600 deg C in air. The influence of temperature on the small fatigue crack behavior in the alloy was investigated. It has been found that the fatigue limit of a plain specimen is determined by the limiting stress for small crack growth and the fatigue strength is the long life region is higher at elevated temperatures than at room temperature, because the early growth of smal cracks is enormously suppressed at elevated temperatures. In the steadystate growth process, however, a crack grows faster at higher temperature due to the decrease of fatigue crack growth resistance. The small crack growth rate can be evaluated by the small crack growth law at both room and elevated temperatures.