EFFECT OF DYNAMIC EMBRITTLEMENT ON FATIGUE CRACK PROPAGATION MECHANISM AND CRACK GROWTH RATE IN IN718 [Keynote]
Hans-Jürgen ChristGrand Ballroom B
IN718 is a commonly used nickel-base alloy for high temperature applications, e.g., in gas and steam turbines. At elevated temperatures, this and other superalloys are prone to the failure mechanism "dynamic embrittlement". In order to reveal the mechanism of dynamic embrittlement, high-temperature fatigue crack propagation tests were carried out at 650°C applying various dwell times and testing frequencies. Most of the tests were performed in laboratory air, but some experiments were run in vacuum as well, in order to eliminate environmental effects and, hence, to define the reference fatigue crack propagation behavior. Based on the results obtained, a model was developed for the range of test parameters, where intergranular and transgranular areas exist side by side in the fracture surface. This model provides a quantitative mechanismen-related description of the effect of dynamic embrittlement on fatigue crack propagation rate.