Mapping Mesoscopic-Microscopic Scale Internal Strains by X-Ray Microdiffraction to Reveal Fatigue Damage

Abstract Owing to their superior mechanical properties, superalloys and other advanced structural materials are widely used under cyclic and thermal loading conditions, where fatigue is a predominant failure mode. Fatigue damage initiates from irreversible cyclic slip accumulation in localized stress concentration regions and is strongly influenced by microstructural features such as slip bands and grain boundaries. Conventional characterization techniques lack the spatial resolution to consistently map internal stresses at mesoscopic to microscopic scales in relation to the crystalline structure. In this study, X-ray microdiffraction was employed as a high-resolution, spatially-resolved technique to quantitatively characterize internal strain distributions within grains in a bulk polycrystalline superalloy subjected to thermal fatigue. The results reveal pronounced stress concentrations associated with slip bands, along with multiscale intragranular and intergranular stress heterogeneities induced by cyclic deformation. X-ray microdiffraction demonstrates strong potential for elucidating the interplay between internal stress, microstructure, and fatigue damage, offering critical insights into the micro-mechanisms of fatigue failure.