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Grain-level heterogeneous deformation was studied in a polycrystalline α-Ti specimen deformed by four-point bending. Dislocation slip activity in the microstructure was investigated by surface slip trace analysis. Three-dimensional-X-ray diffraction (3D-XRD) was used to investigate subsurface lattice rotations and to identify geometrically necessary dislocations (GNDs). The slip systems of local GNDs were analyzed by studying the streaking directions of reflections in corresponding Laue patterns. The analysis performed in one grain indicated that the subsurface GNDs were from the same slip system identified using slip trace analysis in backscattered electron images. A crystal plasticity finite element (CPFE) model was used to simulate deformation of the same microstructural region. The predictions of dislocation slip activity match the general aspects of the experimental observations, including the ability to simulate the activation of different slip systems in grains where multiple slip systems were activated. Prediction of local crystal rotations, however, was the least accurate aspect of the CPFE model. [ABSTRACT FROM AUTHOR]

Abstract: A spatially resolved X-ray diffraction method – with a submicron 3D resolution together with SEM and OIM analysis are applied to understand the arrangements of voids, geometrically necessary dislocations and strain gradient distributions in samples of Al (123) and Cu (001) single crystals shocked to incipient spallation fracture. We describe how geometrically necessary dislocations and the effective strain gradient alter white beam Laue patterns of the shocked materials. Several distinct structural zones are observed at different depths under the impact surface. The density of geometrically necessary dislocations (GNDs) is extremely high near the impact and back surface of the shock recovered crystals. The spall region is characterized by a large density of mesoscale voids and GNDs. The spall region is separated from the impact and back surfaces by compressed regions with high total dislocation density but lower GNDs density. Self-organization of shear bands is observed in the shock recovered Cu single crystal. [Copyright &y& Elsevier]

Abstract: Polychromatic microdiffraction uses small X-ray beams to characterize the local crystallographic structure of materials. When combined with a depth resolving technique called differential aperture microscopy, the phase and local orientation of femto-liter volumes (0.5×0.5×0.7μm3) can be resolved beneath the surface of a sample. In addition, the local elastic strain and dislocation tensors can also be determined and the local dislocation type can be modeled. Here we present recent technical developments, including example applications and emerging research directions. [Copyright &y& Elsevier]

Abstract: Variations in the local crystallographic orientation due to the presence of geometrically necessary dislocations and dislocation boundaries smear the distribution of intensity near Laue reflections. Here, some simple model distributions of geometrically necessary dislocations, GNDs, are used to estimate the dislocation tensor field from the intensity distribution of Laue peaks. Streaking of the Laue spots is found to be quantitatively and qualitatively distinct depending on the ratio between the absorption coefficient and the GND density gradient. In addition, different slip systems cause distinctly different Laue-pattern streaking. Experimental Laue patterns are therefore sensitive to stored dislocations and GNDs. As an example, white beam microdiffraction was applied to characterize the dislocation arrangement in a deformed polycrystalline Ni grain during in situ uniaxial tension. [Copyright &y& Elsevier]

Abstract: We report on three-dimensional spatially resolved X-ray microdiffraction measurements of inhomogeneous deformation within individual polycrystalline grains. These measurements provide new insights into the role of grain boundaries. Particularly striking is the qualitatively different mechanical behavior of subgrain volumes near grain boundaries and triple junctions compared to bulk-grain mechanical behavior. These differences are studied by characterizing the evolution of the local orientation distribution in a polycrystalline Ni sample using polychromatic synchrotron X-ray microdiffraction. Dependence of deformation on grain boundary types and triple junctions is determined. Quantitative distinctions in deformation behavior between low-angle boundaries, special low-energy high-angle boundaries, general high-angle boundaries and triple junctions are characterized in terms of spatially resolved misorientation development and extensions of grain boundary effects. In general, larger lattice misorientations are observed near boundaries with higher grain boundary energy. Special high-coincidence grain boundaries exhibit smaller deformation misorientations than general high-angle grain boundaries. These observations are consistent with the observed increases in ductility in grain boundary engineered materials. [Copyright &y& Elsevier]

The depth-dependent strain gradients near buried interfaces in a model system of NiAl–Mo composite were nondestructively probed with 3-D X-ray microdiffraction. Coupled with micromechanical analysis, our study shows that the relaxation of the residual thermal strains in the NiAl–Mo composites results in the formation of a near-surface “slip zone” with large strain gradients in both the reinforcing Mo fibers and NiAl matrix. Based on these results an approach to calculate the fiber–matrix interface strength for composite materials is suggested. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional spatially resolved strains were mapped in a model NiAl/Mo composite after nanoindentation. The depth-dependent strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length scale using X-ray microdiffraction and compared with a detailed micromechanical stress analysis. It is shown that indentation-induced deformation in the composite material is distinct from deformation expected in a single-phase material. This difference arises in part from residual thermal strains in both phases of the composite in the as-grown state. Interplay between residual thermal strains and external mechanical strain results in a complex distribution of dilatational strain in the Mo fibers and NiAl matrix and is distinct in different locations within the indented area. Reversal of the strain sign (e.g., alternating tensile/compressive/tensile strain distribution) is observed in the NiAl matrix. Bending of the Mo fibers during indentation creates relatively large ∼1.5° misorientations between the different fibers and NiAl matrix. Compressive strain along the 〈001〉 direction reached −0.017 in the Mo fibers and −0.007 in the NiAl matrix. [ABSTRACT FROM AUTHOR]