Strain localization and crack initiation behavior of a PM Ni‐based superalloy: SEM‐DIC characterization and crystal plasticity simulation

The strain localization and crack initiation behavior of a powder metallurgy (PM) nickel-based superalloy FGH4098 under low cycle fatigue (LCF) loads at room temperature is investigated by combining scanning electron microscope (SEM)-digital image correlation (DIC) characterization with crystal plasticity simulation. The elastic anisotropy near annealing twin boundaries contributes to strain localization and results in high propensity of LCF failure. The effect of local microstructure on the fatigue crack initiation at {111} slip bands and tortuous crack propagation is revealed. Meanwhile, local crystal plasticity finite element cyclic deformation simulation is carried out based on explicit microstructure reconstructed from electron backscatter diffraction (EBSD) characterization. Four metrics of accumulated shear strain, effective plastic strain, shear strain energy dissipation density, and Fatemi-Socie parameter are selected as fatigue indicator parameters to predict crack initiation site. Fatemi-Socie parameter is proved to be a promising metric for crack initiation prediction.