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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]

Abstract: Experiments on 99% pure Ni samples have been carried out to investigate the dependence of deformation on grain size. The accumulated strains and texture changes within the grains over the sampling volume were measured by neutron diffraction as a function of (h k l) reflections and sample orientations with respect to the tensile axis. Inhomogeneous developments of strain are found. Large tensile lattice strain was found for reflection (200) in the direction parallel to the loading axis. Sample of smaller grain size displays larger strain magnitude. The overall trend of the lattice strain development predicted by the elasto-plastic self-consistent model agrees with the experiment to within 30% and 50% for the small grain and large grain samples, respectively. [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]

Neutron diffraction residual strain measurements have been made on a tubular structure formed by joining two nickel-based superalloy RR1000 parts by inertia welding. Residual strains in the radial, hoop and axial directions of the tube cross-section have been measured. The corresponding residual stress field has been calculated accounting for the stress-free lattice parameter variations in the region close to the weld line. Tensile residual stresses were observed near the inner diameter of the tube with magnitudes of the order of +500, +1100 and +1300 MPa in the radial, axial and hoop directions, respectively. By comparison near the outer diameter (OD) of the weld the corresponding stresses are of the order of −200, −1000 and 150 MPa. The final stress state reflects the influence of the gripping fixture tooling and thermal gradients during inertia welding. Additional X-ray (at the surface) and hole-drilling (at the near surface) measurements show a steep residual stress gradient in the near surface region. Tensile hoop and axial machining stresses at the surface indicate the potential for improving the inertia weld tooling and the machining parameters used when removing the flash. [Copyright &y& Elsevier]

Abstract: We compare experimental measurements of inhomogeneous plastic deformation in a Ni bicrystal with crystal plasticity simulations. Polychromatic X-ray microdiffraction, orientation imaging microscopy and scanning electron microscopy, were used to characterize the geometrically necessary dislocation distribution of the bicrystal after uniaxial tensile deformation. Changes in the local crystallographic orientations within the sample reflect its plastic response during the tensile test. Elastic strain in both grains increases near the grain boundary. Finite element simulations were used to understand the influence of initial grain orientation and structural inhomogeneities on the geometrically necessary dislocations arrangement and distribution and to understand the underlying materials physics. [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: The manuscript presents a combined experimental/simulation study of the intrinsic strengthening of the material near twin boundaries. Polychromatic X-ray micro Laue diffraction together with electron backscattering diffraction shows that dislocation slippage is suppressed near the twin boundaries. Indentation demonstrates increased hardness in the immediate vicinity of the twin boundary. Distinct slip bands are observed in the interior of the macroscopic ~500μm thick twin. Fast oscillations of lattice rotations are found within each slip band. Crystal plasticity analysis using a spectral formulation finds a similar dependence of the plastic response of the matrix and the twin depending on their orientation and initial structural conditions. [Copyright &y& Elsevier]

Abstract: High-performance Kirkpatrick-Baez (KB) neutron supermirror optics can nondispersively image neutrons to small spots. Ray tracing finds that under many conditions, KB mirrors work near the theoretical limit set by source brilliance and can deliver orders of magnitude greater intensities than is possible with conventional (nonfocusing) neutron optics. In general, KB neutron supermirrors are preferred when the required beam size at the sample is small and when the distance between the optics and the sample is not small. Waveguides with beam definings slits are preferred for very short wavelengths, for big beams and when the slits can be placed very close to the sample. For example, for λ ∼0.1nm, if the distance from the last optical element to the sample is ∼100mm, almost two orders of magnitude greater intensity can be focused onto a 100μm spot with M =3KB supermirrors than with a beam guide and symmetric slits. This is independent of whether the beam guide collimates or condenses the beam so long as without slits the beam is larger than the acceptable beam size at the sample. We describe the ray tracing and phase space arguments that support the use of KB supermirrors for producing intense small beams and describe the performance of a prototype KB device which achieved a 89μm×90μm focus. We briefly describe even more advanced methods that can increase the beam divergence on the sample while maintaining a small beam. [Copyright &y& Elsevier]