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

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Understanding Micromechanical Material Behavior Using Synchrotron X-rays and In Situ Loading MATTHEW P. MILLER, DARREN C. PAGAN, ARMAND J. BEAUDOIN, KELLY E. NYGREN, and DALTON J. SHADLE 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. https://doi.org/10.1007/s11661-020-05888-w Ó The Minerals, Metals & Materials Society and ASM International 2020

I.

INTRODUCTION

THREE-DIMENSIONAL characterization methods have advanced quantitative understanding of the structures, phenomena, and behaviors that are most important for metallic alloy processing and performance design—but there is much yet to learn, even about the processes that seem simplest. Crystal scale elasticity is inherently anisotropic and three-dimensional and produces the stress fields that drive many of the other important and interesting deformation and damage phenomena in a loaded polycrystal. As the load increases, crystal scale yielding seems to initiate at high stress regions, then to spread in often non-intuitive ways; an evolution in yield strength is intimately coupled to an increase in stress. Plasticity, another anisotropic

MATTHEW P. MILLER is with the Sibley School of Mechanical and Aerospace Engineering, Upson Hall, Cornell University, Ithaca, NY 14853 and also with the Cornell High Energy Synchrotron Source, Cornell University, 161 Synchrotron Drive, Ithaca, NY 14853. Contact e-mail: [email protected] DARREN C. PAGAN, ARMAND J. BEAUDOIN, and KELLY E. NYGREN are with the Cornell High Energy Synchrotron Source, Cornell University. DALTON J. SHADLE is with the Sibley School of Mechanical and Aerospace Engineering, Upson Hall, Cornell University. Manuscript submitted March 9, 2020. Article published online June 30, 2020 4