The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
T.j. Ruggles - One of the best experts on this subject based on the ideXlab platform.
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Correlating results from high resolution EBSD with TEM- and ECCI-based Dislocation microscopy: Approaching single Dislocation sensitivity via noise reduction.
Ultramicroscopy, 2019Co-Authors: T.j. Ruggles, Martin A. Crimp, Yung Suk Jeremy Yoo, Bret E. Dunlap, Josh KacherAbstract:Abstract High resolution electron backscatter diffraction (HREBSD), an SEM-based diffraction technique, may be used to measure the lattice distortion of a crystalline material and to infer the geometrically necessary Dislocation Content. Uncertainty in the image correlation process used to compare diffraction patterns leads to an uneven distribution of measurement noise in terms of the lattice distortion, which results in erroneous identification of Dislocation type and density. This work presents a method of reducing noise in HREBSD Dislocation measurements by removing the effect of the most problematic components of the measured distortion. The method is then validated by comparing with TEM analysis of Dislocation pile-ups near a twin boundary in austenitic stainless steel and with ECCI analysis near a nano-indentation on a tantalum oligocrystal. The HREBSD Dislocation microscopy technique is able to resolve individual Dislocations visible in TEM and ECCI and correctly identify their Burgers vectors.
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Dislocation Content measured via 3d hr ebsd near a grain boundary in an alcu oligocrystal
2016Co-Authors: T.j. Ruggles, Jacob D Hochhalter, Eric R HomerAbstract:Interactions between Dislocations and grain boundaries are poorly understood and crucial to mesoscale plasticity modeling. Much of our understanding of Dislocation-grain boundary interaction comes from atomistic simulations and TEM studies, both of which are extremely limited in scale. High angular resolution EBSD-based continuum Dislocation microscopy provides a way of measuring Dislocation activity at length scales and accuracies relevant to crystal plasticity, but it is limited as a two-dimensional technique, meaning the character of the grain boundary and the complete Dislocation activity is difficult to recover. However, the commercialization of plasma FIB dual-beam microscopes have made 3D EBSD studies all the more feasible. The objective of this work is to apply high angular resolution cross correlation EBSD to a 3D EBSD data set collected by serial sectioning in a FIB to characterize Dislocation interaction with a grain boundary. Three dimensional high angular resolution cross correlation EBSD analysis was applied to an AlCu oligocrystal to measure Dislocation densities around a grain boundary. Distortion derivatives associated with the plasma FIB serial sectioning were higher than expected, possibly due to geometric uncertainty between layers. Future work will focus on mitigating the geometric uncertainty and examining more regions of interest along the grain boundary to glean information on Dislocation-grain boundary interaction.
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The effect of length scale on the determination of geometrically necessary Dislocations via EBSD continuum Dislocation microscopy.
Ultramicroscopy, 2016Co-Authors: T.j. Ruggles, Travis Rampton, Ali Khosravani, David T. FullwoodAbstract:Electron backscatter diffraction (EBSD) Dislocation microscopy is an important, emerging field in metals characterization. Currently, calculation of geometrically necessary Dislocation (GND) density is problematic because it has been shown to depend on the step size of the EBSD scan used to investigate the sample. This paper models the change in calculated GND density as a function of step size statistically. The model provides selection criteria for EBSD step size as well as an estimate of the total Dislocation Content. Evaluation of a heterogeneously deformed tantalum specimen is used to asses the method.
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Resolving geometrically necessary Dislocation density onto individual Dislocation types using EBSD-based continuum Dislocation microscopy
International Journal of Plasticity, 2016Co-Authors: T.j. Ruggles, David T. Fullwood, Jeffrey W. KysarAbstract:Abstract Modeling of plasticity is often hampered by the difficulty in accurately characterizing Dislocation density on the microscale for real samples. It is particularly difficult to resolve measured Dislocation Content onto individual Dislocation types at the length scales most commonly of interest in plasticity studies. Methods have been developed to analyze Dislocation Content at the continuum level using the Nye tensor and Kroner's fundamental relation of continuum Dislocation theory to interpret the local strain gradients obtained from high resolution electron backscatter diffraction (HREBSD). This paper assesses an implementation of the Nye–Kroner–Bilby method for resolving measured geometrically necessary Dislocation Content onto individual Dislocation types via a novel simulation of distortion fields around continuum fields of Dislocation density based on classical continuum elasticity equations. It is then applied to HREBSD data for a micro-indented nickel single crystal.
Akira Usui - One of the best experts on this subject based on the ideXlab platform.
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optical detection of electron paramagnetic resonance in low Dislocation Content gan grown by hydride vapor phase epitaxy
Physical Review B, 2002Co-Authors: Cornel Bozdog, G D Watkins, Haruo Sunakawa, Naotaka Kuroda, Akira UsuiAbstract:Three broad overlapping photoluminescence bands, centered at ∼1.75 eV (red), ∼2.2 eV (yellow), and ∼2.33 eV (green), are observed in low-Dislocation-Content GaN grown by the hydride vapor-phase epitaxy method. Optical detection of electron paramagnetic resonance (ODEPR) studies reveal that each is fed by a spin-dependent electron transfer from a shallow donor to a deeper defect, which is different for each of the bands, and different from defects previously found in GaN grown by the more conventional epitaxy methods (metal-organic vapor-phase epitaxy and molecular beam epitaxy). The g-value progression for the deeper defects suggests a two-stage luminescence process in which the luminescence arises from hole capture at the specific defect in each case, after the spin-dependent electron capture process observed by ODEPR. This model also fits for the deep level usually found in the yellow band for more heavily dislocated materials, as originally suggested by Glaser. An additional weak anisotropic ODEPR signal is also observed in the red and yellow bands, None of the signals show resolved hyperfine interactions, and their chemical and/or lattice structures remain unknown.
Martin A. Crimp - One of the best experts on this subject based on the ideXlab platform.
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Correlating results from high resolution EBSD with TEM- and ECCI-based Dislocation microscopy: Approaching single Dislocation sensitivity via noise reduction.
Ultramicroscopy, 2019Co-Authors: T.j. Ruggles, Martin A. Crimp, Yung Suk Jeremy Yoo, Bret E. Dunlap, Josh KacherAbstract:Abstract High resolution electron backscatter diffraction (HREBSD), an SEM-based diffraction technique, may be used to measure the lattice distortion of a crystalline material and to infer the geometrically necessary Dislocation Content. Uncertainty in the image correlation process used to compare diffraction patterns leads to an uneven distribution of measurement noise in terms of the lattice distortion, which results in erroneous identification of Dislocation type and density. This work presents a method of reducing noise in HREBSD Dislocation measurements by removing the effect of the most problematic components of the measured distortion. The method is then validated by comparing with TEM analysis of Dislocation pile-ups near a twin boundary in austenitic stainless steel and with ECCI analysis near a nano-indentation on a tantalum oligocrystal. The HREBSD Dislocation microscopy technique is able to resolve individual Dislocations visible in TEM and ECCI and correctly identify their Burgers vectors.
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Comparison of Dislocation Content measured with transmission electron microscopy and micro-Laue diffraction based streak analysis
Scripta Materialia, 2018Co-Authors: Chen Zhang, Shanoob Balachandran, Philip Eisenlohr, Martin A. Crimp, Carl J. Boehlert, Thomas R. BielerAbstract:Abstract The subsurface Dislocation Content in a Ti-5Al-2.5Sn (wt%) uniaxial tension sample deformed at ambient temperature was characterized by peak streak analysis of micro-Laue diffraction patterns collected non-destructively by differential aperture X-ray microscopy, and with focused ion beam transmission electron microscopy of material in the same volume. This comparison reveals that micro-Laue diffraction streak analysis based on an edge Dislocation assumption can accurately identify the dominant Dislocation slip system history (Burgers vector and plane observed by TEM), despite the fact that Dislocations have predominantly screw character. Other Dislocations identified by TEM were not convincingly discernible from the peak streak analysis.
Thomas R. Bieler - One of the best experts on this subject based on the ideXlab platform.
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Comparison of Dislocation Content measured with transmission electron microscopy and micro-Laue diffraction based streak analysis
Scripta Materialia, 2018Co-Authors: Chen Zhang, Shanoob Balachandran, Philip Eisenlohr, Martin A. Crimp, Carl J. Boehlert, Thomas R. BielerAbstract:Abstract The subsurface Dislocation Content in a Ti-5Al-2.5Sn (wt%) uniaxial tension sample deformed at ambient temperature was characterized by peak streak analysis of micro-Laue diffraction patterns collected non-destructively by differential aperture X-ray microscopy, and with focused ion beam transmission electron microscopy of material in the same volume. This comparison reveals that micro-Laue diffraction streak analysis based on an edge Dislocation assumption can accurately identify the dominant Dislocation slip system history (Burgers vector and plane observed by TEM), despite the fact that Dislocations have predominantly screw character. Other Dislocations identified by TEM were not convincingly discernible from the peak streak analysis.
Niels Hansen - One of the best experts on this subject based on the ideXlab platform.
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Dislocations, boundaries and slip systems in cube grains of rolled aluminium
Scripta Materialia, 2011Co-Authors: Y.l. Wei, Xiaoxu Huang, Andrew Godfrey, Wei Liu, Q. Liu, Niels Hansen, Grethe WintherAbstract:The relationship between the Dislocation Content of boundaries and the active slip systems is explored by characterisation of Burgers vectors, Dislocation lines and relative densities in 11 boundaries in near-cube grains in 10% rolled aluminium. To provide a good basis for comparison, all the boundaries investigated lie in the longitudinal plane. Practically all Dislocations have screw character, with Burgers vectors corresponding to the slip systems predicted active. The Dislocations arrange in a regular grid and the boundaries are most likely low-energy Dislocation structures.
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Slip pattern, microstructure and local crystallography in an aluminium single crystal of brass orientation {110}〈112〉
Acta Materialia, 1998Co-Authors: Andrew Godfrey, D. Juul Jensen, Niels HansenAbstract:Abstract The evolution of microstructure and local crystallography has been examined in pure Al single crystals of {110}〈112〉 orientation (brass or B-orientation) deformed by channel die compression at room temperature to logarithmic strains of ϵ =0.5 and ϵ =1.5. A homogeneous cell block deformation microstructure is seen at the low strain. At higher strain the cell blocks are less distinct and some evidence of strain localisation is observed. A shallow texture gradient is seen, corresponding to a lattice rotation about [101] and consistent with slip occuring on just the two most highly stressed slip systems. However an analysis using the Frank formula of the Dislocation Content for some of the observed boundaries suggests that a significant amount of slip takes place on systems not predicted by a plasticity analysis. This unpredicted slip stabilises the Dislocation walls on planes other than those predicted using the Frank formula.