The resolution dependence of orientation gradients was studied in a well-annealed 99.9995\% pure polycrystalline copper pulled to failure in tension. Owing to the well developed neck, different regions in the sample correspond to different tensile strains. Post-mortem characterization was performed using EBSD on cross-sections containing the tensile axis. Kernel average misorientation (KAM) was calculated as a metric to establish correlation between defect accumulation and microstructural features, with a threshold of 5 degrees to focus on intra-granular gradients. The region with the lowest strain (2\%) showed high KAM values adjacent to grain boundaries compared to the grain interior, regardless of the point spacing, i.e. the spatial resolution. However, in the region with the highest strain (13\%) a strong dependence on resolution was found. For point spacings of 0.5 mu m or smaller, the same correlation of high KAM with locations near boundaries was found. At coarse spacings i.e. low spatial resolution, by contrast, the reverse was found in that the highest KAM values appear in the grain interiors, as previously observed in X-ray microscopy on the same sample which had a similar coarse resolution. An analysis of orientation gradients parallel to, and perpendicular to boundaries suggested that the latter tend to be the larger of the two. This helps to explain why boundary-adjacent points have low KAM values. The conclusion is that measurement of local orientation gradient requires a resolution that is comparable to the dislocation substructure. (C) 2015 Published by Elsevier B.V.

We present an investigation of the effect of deformation twinning on the visco-plastic response and stress localization in a low stacking fault energy twinning-induced plasticity (TWIP) steel under uniaxial tension loading. The three-dimensional full field response was simulated using the fast Fourier transform method. The initial microstructure was obtained from a three dimensional serial section using electron backscatter diffraction. Twin volume fraction evolution upon strain was measured so the hardening parameters of the simple Voce model could be identified to fit both the stress-strain behavior and twinning activity. General trends of texture evolution were acceptably predicted including the typical sharpening and balance between the <111> fiber and the <100> fiber. Twinning was found to nucleate preferentially at grain boundaries although the predominant twin reorientation scheme did not allow spatial propagation to be captured. Hot spots in stress correlated with the boundaries of twinned voxel domains, which either impeded or enhanced twinning based on which deformation modes were active locally.

This work focuses on the major cause of life limiting behavior in Ni-based superalloys for high pressure and temperature turbine disks applications in low cycle fatigue. Specific ideas of local microstructure features, such as the role of as large as (ALA) grains, in promoting slip localization in directly measured 3D microstructures were tested with finite element method (FEM) simulations with crystal plasticity. Synthetic microstructures with experimentally determined microstructurally small fatigue crack weakest link features of ALA grains comprise the test cases. A Rene88 damage tolerant (R88DT) dataset, from electron backscatter diffraction, was used to instantiate approximately 1.5 million elements and 200 grains from FEM sensitivity studies. Changing mesh resolution minimally impacted global damage response, but local convergence required the maximum resolution. The present results help to quantify the deleterious impact of ALA grains in Ni-based superalloys to extend service life.

Atomistic simulations using the embedded atom method were employed to compute the energies of 408 distinct grain boundaries in bcc Fe and Mo. This set includes grain boundaries that have tilt, twist, and mixed character and coincidence site lattices ranging from Sigma 3 to Sigma 323. The results show that grain boundary energies in Fe and Mo are influenced more by the grain boundary plane orientation than by the lattice misorientation or lattice coincidence. Furthermore, grain boundaries with (110) planes on both sides of the boundary have low energies, regardless of the misorientation angle or geometric character. Grain boundaries of the same type in Fe and Mo have strongly correlated energies that scale with the ratio of the cohesive energies of the two metals. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We describe a methodology for calculating approximate, yet accurate analytical expressions for the probability density function of grain diameter as obtained from experimental microstructures. This methodology relies on a novel cumulant expansion that is tailored to the lognormal distribution and provides a systematic description of departures from lognormality. We test our methodology by characterizing two data sets obtained from the microstructures associated with polycrystalline, high-purity Al2O3 samples. The utillity of this approach is demonstrated by a detailed statistical analysis. (C) 2015 Elsevier B.V. All rights reserved.

The resolution dependence of orientation gradients was studied in a well-annealed 99.9995\% pure polycrystalline copper pulled to failure in tension. Owing to the well developed neck, different regions in the sample correspond to different tensile strains. Post-mortem characterization was performed using EBSD on cross-sections containing the tensile axis. Kernel average misorientation (KAM) was calculated as a metric to establish correlation between defect accumulation and microstructural features, with a threshold of 5 degrees to focus on intra-granular gradients. The region with the lowest strain (2\%) showed high KAM values adjacent to grain boundaries compared to the grain interior, regardless of the point spacing, i.e. the spatial resolution. However, in the region with the highest strain (13\%) a strong dependence on resolution was found. For point spacings of 0.5 mu m or smaller, the same correlation of high KAM with locations near boundaries was found. At coarse spacings i.e. low spatial resolution, by contrast, the reverse was found in that the highest KAM values appear in the grain interiors, as previously observed in X-ray microscopy on the same sample which had a similar coarse resolution. An analysis of orientation gradients parallel to, and perpendicular to boundaries suggested that the latter tend to be the larger of the two. This helps to explain why boundary-adjacent points have low KAM values. The conclusion is that measurement of local orientation gradient requires a resolution that is comparable to the dislocation substructure. (C) 2015 Published by Elsevier B.V.

We present an investigation of the effect of deformation twinning on the visco-plastic response and stress localization in a low stacking fault energy twinning-induced plasticity (TWIP) steel under uniaxial tension loading. The three-dimensional full field response was simulated using the fast Fourier transform method. The initial microstructure was obtained from a three dimensional serial section using electron backscatter diffraction. Twin volume fraction evolution upon strain was measured so the hardening parameters of the simple Voce model could be identified to fit both the stress-strain behavior and twinning activity. General trends of texture evolution were acceptably predicted including the typical sharpening and balance between the <111> fiber and the <100> fiber. Twinning was found to nucleate preferentially at grain boundaries although the predominant twin reorientation scheme did not allow spatial propagation to be captured. Hot spots in stress correlated with the boundaries of twinned voxel domains, which either impeded or enhanced twinning based on which deformation modes were active locally.