High-Resolution Single-Grain Diffraction of Polycrystalline Materials

Polycrystalline bulk materials are ubiquitous in everyday life, including biological, geological, and engineered structural and functional materials. Their fundamental units are individual grains, which are characterized by their microstructure; i.e., the arrangement of lattice defects. The microstructure usually influences the materials properties critically

Characterization of Irradiation Damage Using X-Ray Diffraction Line-Profile Analysis

During operation, structural components made of zirconium alloys are subject toneutron irradiation, which leads to the displacement of zirconium atoms fromtheir lattice sites, the production of self-interstitials and vacancies, and eventually dislocation loops. This process can lead to deleterious effects such as irradiation growth, creep, and embrittlement as well as accelerated aqueous corrosion. Quantitative analysis of dislocation line densities is seen as an importantpathway for distinguishing between the irradiation response of different alloys.The analysis of irradiation damage using X-ray diffraction (XRD) line-profile analysis has proven to be a powerful complementary technique to transmissionelectron microscopy, which samples a comparatively large volume and is lessaffected by the subjectivity of image analysis. In this paper we present andanalyze three different types of XRD experiments, describing their purpose andthe new insight achieved using each technique. First, we present work carriedout on neutron-irradiated samples, comparing dislocation line densities measured by XRD with macroscopic growth measurements. A second experimentusing a synchrotron-based X-ray microbeam enabled the mapping of dislocationline densities as a function of depth from the surface of proton-irradiated zirconium alloys. These data are compared with calculated damage profiles, providingnew insight into the early saturation of damage. Finally, the last example presented here focuses on synchrotron-based 3D XRD measurements, for whichdislocation-loop line densities were analyzed in hundreds of individual grains,providing excellent statistics about the grain-to-grain variability of line densities

Dislocations and crystallite-size distribution in nanocrystalline CeO2 obtained from an ammonium cerium(IV) nitrate solution

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Elucidating microstructural evolution and strengthening mechanisms in nanocrystalline surface induced by surface mechanical attrition treatment of stainless steel

Surface mechanical attrition treatment (SMAT) is a high strain and strain rate severe plastic deformation (SPD) technique for surface nanocrystallization of metals. The aim of this study was to investigate the mechanism of nanocrystallization and strengthening in a medium stacking fault energy 316 L austenitic stainless steel during SMAT. The paramount role of microband and shear band formation in nano crystallization is outlined, as opposed to deformation twinning previously reported in low SFE austenitic stainless steels. Shear bands undergo dynamic recrystallization and recrystallization twinning to produce ultra-fine grains in contrast to twin-twin intersections in low SFE stainless steel. The ultra-fine grains further sub-divide into smaller cells with initially low misorientation. Nanocrystallization occurs when misorientation between these cells increases with further strain. The additivity of strengthening by dislocation density and grain size is studied. Dislocation density was neglected in previous studies while studying strengthening mechanisms in SMAT processed materials. This study illustrates that dislocation density cannot be ignored as the strengthening mechanism in SMAT process. The grain size and dislocation density both significantly contribute to overall strengthening in SMAT processed microstructure. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved