How would you… …describe the overall significance of this paper? This paper describes emerging characterization experiments referred to as High Energy Diffraction Microscopy conducted at the Advanced Photon Source (APS) beam line 1-ID-C. "Near field" diffraction is used to quantify three-dimensional orientation maps of polycrystalline samples non-destructively, with incredible detail grain boundary geometry. "Far field" experiments are used to quantify lattice strains and single crystal stress states within large aggregates subjected to in situ loading. …describe this work to a materials science and engineering professional with no experience in your technical specialty? Materials derive their mechanical properties from their internal structure. As engineering moves downscale, it becomes more important to quantify the structure and mechanical response of engineering materials on small size scales. High energy x-ray diffraction methods are rapidly evolving into important microscale characterization tools that can be used together with high fidelity mechanical models. …describe this work to a layperson? Micro-and nano-engineering methods hold enormous promise for a broad spectrum of products and processes. The determination of material attributes and mechanical properties on small size scales is one of the main barriers to moving down scale. Instead of making tiny specimens, we examine deforming test samples using high energy x-rays, created using a special national laboratory facility. This work will enable us to precisely reconstruct the internal structure of engineering alloys and will provide important mechanical data on the micron scale. The status of the High Energy Diffraction Microscopy (HEDM) program at the 1-ID beam line of the Advanced Photon Source is reported. HEDM applies high energy synchrotron radiation for the grain and sub-grain scale structural and mechanical characterization of polycrystalline bulk materials in situ during thermomechanical loading. Case studies demonstrate the mapping of grain boundary topology, the evaluation of stress tensors of individual grains during tensile deformation and comparison to a finite element modeling simulation, and the characterization of evolving dislocation structure. Complementary information is obtained by post mortem electron microscopy on the same sample volume previously investigated by HEDM.

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The evolution of the crystallographic orientation field in a polycrystalline sample of copper is mapped in three dimensions as tensile strain is applied. Using forward‐modeling analysis of high‐energy X‐ray diffraction microscopy data collected at the Advanced Photon Source, the ability to track intragranular orientation variations is demonstrated on an ∼2 µm length scale with ∼0.1° orientation precision. Lattice rotations within grains are tracked between states with ∼1° precision. Detailed analysis is presented for a sample cross section before and after ∼6% strain. The voxel‐based (0.625 µm triangular mesh) reconstructed structure is used to calculate kernel‐averaged misorientation maps, which exhibit complex patterns. Simulated scattering from the reconstructed orientation field is shown to reproduce complex scattering patterns generated by the defected microstructure. Spatial variation of a goodness‐of‐fit or confidence metric associated with the optimized orientation field indicates regions of relatively high or low orientational disorder. An alignment procedure is used to match sample cross sections in the different strain states. The data and analysis methods point toward the ability to perform detailed comparisons between polycrystal plasticity computational model predictions and experimental observations of macroscopic volumes of material.

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International audienceThree-dimensional near-field high-energy X-ray diffraction microscopy has been used to observe the formation of new twinned grains in high purity Ni during annealing at 800 °C. In the fully recrystallized microstructure annealed at 800 °C, twinned grains form along triple lines. Both the grain boundary character and the grain boundary dihedral angles were measured before and after the twin formed. These measurements make it possible to show that although each new twinned grain increases the total grain boundary area, it reduces the total grain boundary energy

Revising grain growth Polycrystalline materials will often coarsen during annealing, a process that can modify the physical properties. A generally accepted theory ties the grain boundary curvature to the velocity at which grain boundaries migrate. Bhattacharya et al . measured this relationship for 52,000 grains in a nickel sample. They did not observe any relationship between curvature and velocity, suggesting that this accepted theory is not robust for polycrystalline samples. The observations require grain-coarsening models to be updated to more accurately predict the effects of annealing. —BG

We describe our recent work on developing X-ray diffraction microscopy as a tool for studying three dimensional microstructure dynamics. This is a measurement technique that is demanding of experimental hardware and presents a challenging computational problem to reconstruct the sample microstructure. A dedicated apparatus exists at beamline 1-ID of the Advanced Photon Source for performing these measurements. Submicron mechanical precision is combined with focusing optics that yield ≈2μmhigh×1.3mm wide line focused beam at 50keV. Our forward modeling analysis approach generates diffraction from a simulated two dimensional triangular mesh. Each mesh element is assigned an independent orientation by optimizing the fit to experimental data. The method is computationally demanding but is adaptable to parallel computation. We illustrate the state of development by measuring and reconstructing a planar section of an aluminum polycrystal microstructure. An orientation map of ∼90 grains is obtained along with a map showing the spatial variation in the quality of the fit to the data. Sensitivity to orientation variations within grains is on the order of 0.1deg. Volumetric studies of the response of microstructures to thermal or mechanical treatment will soon become practical. It should be possible to incorporate explicit treatment of defect distributions and to observe their evolution.

A microstructure-based capability for forecasting microcrack nucleation in the nickel-based superalloy LSHR is proposed, implemented, and partially verified. Specifically, gradient crystal plasticity is applied to finite-element models of the experimentally measured, 3D microstructure wherein a microcrack is known to have nucleated along a coherent Σ3 boundary. The framework is used to analyze this particular nucleation event and conduct an extensive grain boundary analysis study, the results of which underpin the importance that elastic anisotropy and coherency have in the localization of plastic slip.