Mapping Residual Microstress by X-ray microdiffraction for Revealing Fatigue Damage

Development of micro-stresses in engineering alloys greatly affects the fatigue behavior. It is difficult to measure directly the micro-stress by traditional X-ray diffraction methods due to the limitation of effective gauge. With the rapid progress in synchrotron-based X-ray techniques, the three-dimensional (3D) stress fields can be directly traced on submicrometer scale through which fatigue deformation damage can be well characterized in polycrystalline materials and single crystal. The examples will be shown in the talk on studies of fatigue damage and cracking in stainless steel and superalloys after cyclic loading, with a focus on important experimental findings on microscopic mechanisms related to fatigue deformation. Moreover, it will be presented a correlative three-dimensional X-ray microscopy framework that integrates microdiffraction and microtomography techniques for capturing morphological and micromechanical field information from the interior of post-mortem metals. The quantitative and statistical understanding of localized strain accumulation related to defect clusters is enabled for revealing the interplay between fatigue microcracking and defect-mediated irreversible localized plasticity during cyclic loading.