The Experts below are selected from a list of 6603 Experts worldwide ranked by ideXlab platform

David J. Dingley - One of the best experts on this subject based on the ideXlab platform.

  • Orientation Imaging Microscopy for the Transmission Electron Microscope
    Microchimica Acta, 2006
    Co-Authors: David J. Dingley
    Abstract:

    The resolution limit of Orientation Imaging Microscopy in the Scanning Electron Microscope is between 20 nA and 80 nA depending on the basic resolution/beam current performance of the SEM, the sample atomic number and the level of residual strain within it. The newer technique of Orientation Imaging in the transmission electron microscope, TEM, improves on this resolution limit by a factor of five to ten. The new technique is based on a novel procedure for determining the crystallography of separate small volumes in the sample by examination of a large series of dark field images. Each image is recorded for a different diffraction condition. This is achieved by using a computer to direct the electron beam onto the same area of the sample so that it covers all directions within a cone of semi-apex angle 3 degrees. Analysis of the intensity of the same point in each of the dark field images permits reconstruction of a diffraction pattern for that point providing the data to calculate its crystal Orientation. The process is repeated for each point in the image. The Orientation Image Micrograph is constructed from the Orientations so determined. The technique is shown to be capable of producing Orientation micrographs of high spatial resolution for unstrained samples. For highly strained samples difficulties are encountered in accurately indexing the complicated diffraction patterns that are observed. Methods to improve the indexing procedures involve determining the sub-cell structure first from a comparison of patterns from adjacent pixels and then summing all patterns belonging to a single sub-cell. The resultant improvement in pattern quality permits more reliable determination of Orientation. Examples of this procedure are taken from studies of deformed aluminum.

  • Progressive steps in the development of electron backscatter diffraction and Orientation Imaging Microscopy.
    Journal of microscopy, 2004
    Co-Authors: David J. Dingley
    Abstract:

    Ten years ago electron backscatter diffraction (EBSD) became available to a wider group active in materials research. This paper highlights some of the more significant developments in camera technology and software developments that have arisen since then. The use of slow-scan charge couple device cameras for phase identification and rapid determination of Orientation image micrographs is reviewed. The current limiting spatial resolution of the technique is shown to be less than 10 nm. A procedure for improving lattice spacing measurement by utilizing the full resolution of the camera is described with experimental measurements on silicon and nickel showing relative errors of plus/minus 3%. An investigation of partially recrystallized aluminium shows how the recrystallized fraction can be extracted with confidence but that the mapping of substructure in the highly deformed regions is questionable. Phase identification is described for complex cases in which the phase data tabulated in standard databases do not correspond to what is observed in the EBSD patterns. Phase mapping in a complex mineral in which chemical data and EBSD data are collected simultaneously is shown to be improved by recording both the chemical and the EBSD data into computer memory and proceeding with the phase discrimination and Orientation measurement in off-line analysis.

  • Fast Orientation Imaging Microscropy
    Microscopy Today, 2002
    Co-Authors: David J. Dingley, Stuart I. Wright, Mathew M. Nowell
    Abstract:

    Orientation Imaging Microscopy is currently the most rapidly growing combined metallographic and crystallographic technique today. The first OIM was recorded by Wright in 1991, and published soon after, Adams et al. (1993). The technique is based on the original works on Electron Backscatter Diffraction (EBSD) by Venables and Hariand (1973), and Dingiey (1984, 1987). By 1994 some number of papers on the subject had been published. At the time of writing the authors are aware of over 600 publications that have utilized the technique and there are in excess of 400 systems in use worldwide.

  • electron backscatter diffraction and Orientation Imaging Microscopy
    Materials Science and Technology, 1997
    Co-Authors: David J. Dingley, David P Field
    Abstract:

    AbstractAn overview of electron backscatter diffraction is presented in which experimental procedures are reviewed together with a basic theoretical description of the mechanism of pattern generation. Manual and automated indexing procedures are described. The new technique of Orientation Imaging Microscopy is presented, with examples from recrystallised AI-Mg alloy, deformed superplastic material, and fractured nickel base alloy.

  • Determining deformation, recovery and recrystallization fractions from Orientation Imaging Microscopy (OIM) data
    Proceedings annual meeting Electron Microscopy Society of America, 1996
    Co-Authors: S.i. Wright, David J. Dingley, David P Field
    Abstract:

    While Orientation Imaging Microscopy (OIM) via automatic analysis of electron backscatter diffraction patterns (EBSPs) has become routine, methods for analyzing results obtained by OIM are still maturing. Interrogating the OIM data to distinguish between deformed, recovered and recrystallized material in a polycrystalline sample is one example. An advantage for using OIM data in such a case is that the corresponding textures can also be determined approaches for distinguishing between these structures from OIM data on a sample of partially recrystallized low-alloy steel.

Wp Willem Pier Vellinga - One of the best experts on this subject based on the ideXlab platform.

  • Effects of crystal structure and grain Orientation on the roughness of deformed polycrystalline metals
    Acta Materialia, 2006
    Co-Authors: O. Wouters, Wp Willem Pier Vellinga, R. Van Tijum, J.th.m. De Hosson
    Abstract:

    Abstract Surface roughening during tensile deformation of polycrystalline aluminum, iron and zinc is investigated using white light confocal Microscopy and Orientation Imaging Microscopy. A height–height correlation technique is used to analyze the data. The surface obeys self-affine scaling on length scales up to a correlation length which approximately equals the grain size and above which no height correlation is present. The self-affine scaling exponent increases initially with strain and saturates at a value around 0.9 for aluminum and at 0.8 for iron and zinc. A linear relation is observed between root mean square roughness and strain. The observed grain scale roughening is explained as arising from Orientation differences between neighboring grains and depends on the available number of slip systems in the material. Orientation Imaging Microscopy is used to investigate the influence of the Orientation of the surface grains and subsurface grains on the topography. It is found that the Schmid factor of surface grains alone is not enough to predict local deformation and evolution of surface height. In particular, grains with high Schmid factor may show less deformation than expected. It is shown that subsurface grains influence the roughness and it is hypothesized that a high cumulative Schmid factor on a cross-section below a point at the surface leads to a depression at the surface.

  • Correlation between thermal fatigue and thermal anisotropy in a Pb-free solder alloy
    Scripta Materialia, 2005
    Co-Authors: Ma Matin, Ewc Erica Coenen, Wp Willem Pier Vellinga, Mgd Marc Geers
    Abstract:

    Intrinsic thermal fatigue in a mechanically unconstrained Pb-free, Sn-rich Sn–3.8Ag–0.7Cu alloy has been investigated under cyclic thermal loading between 293 K and 353 K. Fatigue damage is shown to occur preferentially along high angle grain boundaries. From a combination of Orientation Imaging Microscopy and finite element modelling it appears that this fatigue damage and stresses resulting from the thermal anisotropy of Sn are highly correlated.

  • Correlation between thermal fatigue and thermal anisotropy in a Sn-rich solder alloy
    EuroSimE 2005. Proceedings of the 6th International Conference on Thermal Mechanial and Multi-Physics Simulation and Experiments in Micro-Electronics , 1
    Co-Authors: Ma Matin, Wp Willem Pier Vellinga, E.w.c. Coenen, Marc G. D. Geers
    Abstract:

    Intrinsic thermal fatigue in a mechanically unconstrained Sn-rich Sn-3.8Ag-0.7Cu alloy has been investigated under cyclic thermal loading within the temperature range of 293 K to 353 K. Fatigue damage resulting from this cycling is shown to occur preferentially along some grain boundaries. From a combination of Orientation Imaging Microscopy and finite element modelling it appears that fatigue damage and stresses resulting from the thermal anisotropy of Sn are highly correlated.

Mgd Marc Geers - One of the best experts on this subject based on the ideXlab platform.

Ma Matin - One of the best experts on this subject based on the ideXlab platform.

Brent L. Adams - One of the best experts on this subject based on the ideXlab platform.

  • High Resolution Orientation Imaging Microscopy
    2012
    Co-Authors: David T. Fullwood, Brent L. Adams
    Abstract:

    Abstract : This report summarizes the progress and achievements resulting from the Army Research Office grant number WF911NF-08-1-0350 on the subject of High Resolution Orientation Imaging Microscopy. The central technical outcome of the project is a new methodology for extracting high-resolution structure data from crystalline materials that uncovers a wealth of new microstructure information including absolute strain, geometrically necessary dislocations, and improved Orientation measurements. The framework has been patented, and a commercialization agreement is in place to disseminate the new capabilities to the scientific community. New insights into deformation processes in magnesium, nickel, tantalum, iron, copper and various other metals have already arisen. The results have been widely published via journals, books and conferences. Four graduate students have been funded by this grant; two have earned PhDs, and two are on track to complete PhDs. Three students have been awarded NSF or NDSEG fellowships as a direct result of the research opportunities afforded by this grant to undergraduate students. Various other undergraduate students have been funded and have moved on to graduate school.

  • Orientation Imaging Microscopy investigation of the compression deformation of a [011] ta single crystal
    Journal of Engineering Materials and Technology, 1999
    Co-Authors: Adam J. Schwartz, Wayne E. King, J.s. Stölken, G.h. Campbell, D.h. Lassila, S. Sun, Brent L. Adams
    Abstract:

    High-purity tantalum single crystal cylinders oriented with [110] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The samples were subsequently sectioned for characterization using Orientation Imaging Microscopy (O&I) along two orthogonal sectioning planes: one in the plane containing [001] and [110] (longitudinal) and the other in the plane containing [1{anti 1}0] and[110] (transverse). To examine local lattice rotations, the Euler angles relative to a reference angle at the section center were decomposed to their in-plane and out-of-plane components. The in-plane and out-of-plane misOrientation maps for all compression tests reveal inhomogeneous deformation everywhere and particularly large lattice rotations in the comers of the longitudinal section. Of particular interest are the observed alternating Orientation changes. This suggests the existence of networks of dislocations with net alternating sign that are required to accommodate the observed rotations. Rotation maps from the transverse section are distinctly different in appearance from those in the longitudinal plane. However, the rotation maps confirm that the rotations observed above were about the [1{anti 1}0] axis. Alternating Orientation changes are also observed on this section. Results will be directly compared with crystal rotations predicted using finite element methods and reviewed in light of the LLNL Multiscale Materials Modeling Program.

  • Analysis of compression behavior of a [011] Ta single crystal with Orientation Imaging Microscopy and crystal plasticity
    1999
    Co-Authors: Brent L. Adams, Wayne E. King, J.s. Stölken, G.h. Campbell, D.h. Lassila, S. Sun, A. J. Swartz
    Abstract:

    High-purity tantalum single crystal cylinders oriented with [011] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The engineering stress-strain curve exhibited an up-turn at strains greater than {approximately}20% while the samples took on an ellipsoidal shape during testing, elongated along the [100] direction with almost no dimensional change along [0{bar 1}1]. Two orthogonal planes were selected for characterization using Orientation Imaging Microscopy (OIM): one plane containing [100] and [011] (longitudinal) and the other in the plane containing [0{bar 1}1] and [011] (transverse). OIM revealed patterns of alternating crystal rotations that develop as a function of strain and exhibit evolving length scales. The spacing and magnitude of these alternating misOrientations increases in number density and decreases in spacing with increasing strain. Classical crystal plasticity calculations were performed to simulate the effects of compression deformation with and without the presence of friction. The calculated stress-strain response, local lattice reOrientations, and specimen shape are compared with experiment.

  • Adaptive Orientation Imaging Microscopy
    Microscopy and Microanalysis, 1999
    Co-Authors: W. Yang, Brent L. Adams, M. De Graef
    Abstract:

    This paper describes a new form of Orientation Imaging Microscopy: Adaptive Orientation Imaging Microscopy or AOIM. In standard OIM experiments the local Orientation of the crystal lattice is determined with respect to a suitable reference frame by acquiring and indexing electron back-scattering (EBS) patterns on a square or hexagonal grid of sampling points. Since its invention, OIM has been extensively used to characterize polycrystalline materials. With the fast development of computers and CCD camera systems in the past few years, the standard OIM can now acquire and index of the order of 4000 EBS patterns per hour.In a typical OIM experiment one is usually interested in either the overall texture of. the sample, or in the types and relative frequencies of grain boundaries. In the former case the proper way of acquiring Orientation data involves the use of an equidistant grid of sampling points. In the latter case, however, a large fraction of the acquisition time is wasted sampling the grain interior, which does not provide any information about the grain boundaries.

  • Orientation Imaging Microscopy: Emerging and future applications
    Ultramicroscopy, 1997
    Co-Authors: Brent L. Adams
    Abstract:

    Abstract Orientation Imaging Microscopy (OIM), which images the microstructure using the electron backscattered diffraction probe, has proven to be a powerful tool for the study of polycrystalline materials. OIM's chief strength lies in its ability to couple the morphological aspects of microstructure, with lattice Orientation. With spatial and angular resolution of at least 100 nm and 1°, OIM is ideally suited to investigations at the mesoscale. In this paper three examples are described which illustrate emerging and future applications of OIM to important problems in materials science at the mesoscale. The first example is the use of higher-order point statistics to obtain improved bounds on structure-insensitive properties. It is emphasized that the approach may be used, not only to enhance material properties, but also to control their variability. The second example is an emerging analysis to map the relationships between the character (type) of grain boundaries and their intrinsic properties. The main idea is illustrated for mappings linking character and excess free energy. The third example focuses on the ability of OIM to measure lattice curvature, and to thereby obtain information about the geometrically necessary dislocation content of the microstructure. This example is illustrated by analysis to extract the dislocation density tensor.