Fatigue Strength Reduction Factor for Polycrystalline Nickel Base Superalloy with and without Non-Metallic Inclusions

Polycrystalline nickel base superalloy is popular for its wide applications; it is used in hot sections of power generation turbines, rocket engines and other challenging conditions due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. However, the presence of inclusions introduced into the superalloy during the fabrication processes can significantly degrade the fatigue life. This paper utilizes a new probabilistic method which captures both the essence of microstructure and notch root stress gradient to determine the notch size and inclusions effects on the fatigue strength of notched nickel base superalloy with and without non-metallic inclusions. Notched cylindrical specimens of nickel base superalloy of varying notch root radii are modeled using microstructural-sensitive crystal plasticity finite element codes. The stresses extracted from the fatigue damage process zone around the notch are used in determining the fatigue strength reduction factor and the associated probability of failure of the notched specimens. The numerical results obtained are in direct correlation with the experimentally obtained value for the different notch root radii.