Understanding Micromechanical Material Behavior Using Synchrotron X-rays and In Situ Loading

With the flux of high-energy, deeply penetrating X-rays that a 3rd-generation synchrotron source can provide and the current generation of large fast area detectors, the development and use of synchrotron X-ray methods have experienced impressive growth over the past two decades. This paper describes the current state of an important subset of synchrotron methods—high-energy X-ray diffraction employing in situ loading. These methods, which are known by many acronyms such as 3D X-ray diffraction (3DXRD), diffraction contrast tomography (DCT), and high-energy X-ray diffraction microscopy (HEDM), have shifted the focus of alloy characterization to include crystal scale behaviors in addition to microstructure and have made it possible to track the evolution of a polycrystalline aggregate during loading conditions that mimic alloy processing or in-service conditions. The paper is delineated into methods for characterizing elastic behavior including measuring the stress tensor experienced by each crystal and the inelastic response including crystal plasticity, phase transformations, and the onset of damage. We discuss beam size and detector placement, resolution, and speed in the context of the spatial and temporal resolution and scope of the resulting data. Work that emphasizes material models and the interface of data with various numerical simulations and machine learning is presented.