Fatigue crack initiation, slip localization and twin boundaries in a nickel-based superalloy

The study of fatigue in metals, and fatigue initiation specifically, lends itself to analysis via an emerging set of characterization and modeling tools that describe polycrystals on the meso- or microstructural length scale. These include three-dimensional characterization techniques, elastic anisotropic and visco-plastic stress models, new approaches to the statistical description of stress and strain distributions, synthetic microstructure modeling, and improved tools for manipulating the large datasets generated. A specific example of analysis in both 2D and 3D of fatigue cracks in a nickel-based superalloy is given where all the cracks are effectively coincident with coherent twin boundaries. A spectral method is used to analyze the stress state based on a fully anisotropic elastic calculation. The results indicate that, although a high resolved shear stress is associated with the locations of the observed cracks, the length of the trace of the twin boundary is more strongly correlated with crack formation.