Applications of Multivariate Statistical Methods and Simulation Libraries to Analysis of Electron Backscatter Diffraction and Transmission Kikuchi Diffraction Datasets
Wilkinson, AJ, Collins, DM, Zayachuk, Y, Korla, R, Vilalta-Clemente, A
Journal article
Multivariate statistical methods are widely used throughout the sciences,
including microscopy, however, their utilisation for analysis of electron
backscatter diffraction (EBSD) data has not been adequately explored. The basic
aim of most EBSD analysis is to segment the spatial domain to reveal and
quantify the microstructure, and links this to knowledge of the crystallography
(eg crystal phase, orientation) within each segmented region. Two analysis
strategies have been explored; principal component analysis (PCA) and k-means
clustering. The intensity at individual (binned) pixels on the detector were
used as the variables defining the multidimensional space in which each pattern
in the map generates a single discrete point. PCA analysis alone did not work
well but rotating factors to the VARIMAX solution did. K-means clustering also
successfully segmented the data but was computational more expensive. The
characteristic patterns produced by either VARIMAX or k-means clustering
enhance weak patterns, remove pattern overlap, and allow subtle effects from
polarity to be distinguished. Combining multivariate statistical analysis (MSA)
approaches with template matching to simulation libraries can significantly
reduce computational demand as the number of patterns to be matched is
drastically reduced. Both template matching and MSA approaches may augment
existing analysis methods but will not replace them in the majority of
applications.
AstroEBSD: exploring new space in pattern indexing with methods launched from an astronomical approach
Britton, TB, Tong, V, Hickey, J, Foden, A, Wilkinson, A
Journal article
Electron backscatter diffraction (EBSD) is a technique used to measure
crystallographic features in the scanning electron microscope. The technique is
highly automated and readily accessible in many laboratories. EBSD pattern
indexing is conventionally performed with raw electron backscatter patterns
(EBSPs). These patterns are software processed to locate the band centres (and
sometimes edges) from which the crystallographic index of each band is
determined. Once a consistent index for many bands are obtained, the crystal
orientation with respect to a reference sample & detector orientation can be
determined and presented. Unfortunately, due to challenges related to crystal
symmetry, there are limited available pattern indexing approaches and this has
likely hampered open development of the technique. In this manuscript, we
present a new method of pattern indexing, based upon a method with which
satellites locate themselves in the night sky, and systematically demonstrate
its effectiveness using dynamical simulations and real experimental patterns.
The benefit of releasing this new algorithm is demonstrated as we utilise this
indexing process, together with dynamical solutions, to provide some of the
first accuracy assessments of an indexing solution. In disclosing a new
indexing algorithm, and software processing tool-kit, we hope this opens up
EBSD developments to more users. The software code and example data is released
alongside this article for 3rd party developments.
Indexing Electron Backscatter Diffraction Patterns with a Refined Template Matching Approach
Foden, A, Collins, D, Wilkinson, A, Britton, TB
Internet publication
Electron backscatter diffraction (EBSD) is a well-established method of
characterisation for crystalline materials. This technique can rapidly acquire
and index diffraction patterns to provide phase and orientation information
about the crystals on the material surface. The conventional analysis method
uses signal processing based on a Hough/Radon transform to index each
diffraction pattern. This method is limited to the analysis of simple geometric
features and ignores subtle characteristics of diffraction patterns, such as
variations in relative band intensities. A second method, developed to address
the shortcomings of the Hough/Radon transform, is based on template matching of
a test experimental pattern with a large library of potential patterns. In the
present work, the template matching approach has been refined with a new cross
correlation function that allows for a smaller library and enables a dramatic
speed up in pattern indexing. Refinement of the indexed orientation is
performed with a follow-up step to allow for small alterations to the best
match from the library search. The orientation is further refined with rapid
measurement of misorientation using whole pattern matching. The refined
template matching approach is shown to be comparable in accuracy, precision and
sensitivity to the Hough based method, even exceeding it in some cases, via the
use of simulations and experimental data collected from a silicon single
crystal and a deformed {\alpha}-iron sample. The drastic speed up and pattern
refinement approaches should increase the widespread utility of pattern
matching approaches.
<a href="http://arxiv.org/abs/1807.11313v1">http://arxiv.org/abs/1807.11313v1</a>
Mapping the full lattice strain tensor of a single dislocation by High Angular Resolution Transmission Kikuchi Diffraction (HR-TKD)
Yu, H, Liu, J, Karamched, P, Wilkinson, AJ, Hofmann, F
Journal article
The full lattice strain tensor and lattice rotations induced by a dislocation
in pure tungsten were mapped using high-resolution transmission Kikuchi
diffraction (HR-TKD) in a SEM. The HR-TKD measurement agrees very well with a
forward calculation using an elastically isotropic model of the dislocation and
its Burgers vector. Our results demonstrate that the spatial and angular
resolution of HR-TKD in SEM is sufficiently high to resolve the details of
lattice distortions near individual dislocations. This capability opens a
number of new interesting opportunities, for example determining the Burgers
vector of an unknown dislocation in a fast and straightforward way.
cond-mat.mtrl-sci, cond-mat.mtrl-sci
Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine
Kumamoto, KM, Thom, CA, Wallis, D, Hansen, LN, Armstrong, DEJ, Warren, JM, Goldsby, DL, Wilkinson, AJ
Journal article
|
Science Advances
The impact of water on slip system activity in olivine and the formation of bimodal crystallographic preferred orientations
Wallis, D, Hansen, LN, Tasaka, M, Kumamoto, KM, Parsons, AJ, Lloyd, GE, Kohlstedt, DL, Wilkinson, AJ
