arXiv subjects

Thomas Benjamin Britton

Publications and source records attributed to Thomas Benjamin Britton.

7 recordsLinked to original sources

arXiv2021

Effective structural unit analysis in hexagonal close packed alloys -- reconstruction of parent beta microstructures & crystal orientation post processing analysis

Materials with an allotropic phase transformation can result in the formation of microstructures where grains have orientation relationships (ORs) determined by the transformation history. These microstructures influence the final material properties. In zirconium alloys, there is a solid-state body centred cubic (BCC) to hexagonal close packed (HCP) phase transformation, where the crystal orientations of the HCP phase can be related to the parent BCC structure via the Burgers orientation relationship (BOR). In the present work, we adapt a reconstruction code developed for steels which uses a Markov Chain clustering algorithm to analyse electron backscatter diffraction (EBSD) maps and apply this to the HCP and BCC BOR. This algorithm is released as open-source code (via github, as ParentBOR). The algorithm enables new post processing of the original and reconstructed data set to analyse the variants of the HCP alpha-phase that are present and understand shared crystal planes and shared lattice directions within each parent beta grain, and we anticipate that this assists in understanding the transformation related deformation properties of the final microstructure. Finally, we compare the ParentBOR code with recently released reconstruction codes implemented in MTEX to reveal differences and similarities in how the microstructure is described.

cond-mat.mtrl-sci↗

arXiv2020

TrueEBSD: correcting spatial distortions in electron backscatter diffraction maps

Electron backscatter diffraction (EBSD) in the scanning electron microscope is routinely used for microstructural characterisation of polycrystalline materials. Maps of EBSD data are typically acquired at high stage tilt and slow scan speed, leading to tilt and drift distortions that obscure or distort features in the final microstructure map. In this paper, we describe TrueEBSD, an automatic postprocessing procedure for distortion correction with pixel-scale precision. Intermediate images are used to separate tilt and drift distortion components and fit each to a physically-informed distortion model. We demonstrate TrueEBSD on three case studies (titanium, zirconium and hydride containing Zr), where distortion removal has enabled characterisation of otherwise inaccessible microstructural features.

cond-mat.mtrl-sci↗

arXiv2019

Gazing at crystal balls: Electron backscatter diffraction pattern analysis and cross correlation on the sphere

We present spherical analysis of electron backscatter diffraction (EBSD) patterns with two new algorithms: (1) band localisation and band profile analysis using the spherical Radon transform; (2) orientation determination using spherical cross correlation. These new approaches are formally introduced and their accuracies are determined using dynamically simulated patterns. We demonstrate their utility with an experimental dataset obtained from ferritic iron. Our results indicate that the analysis of EBSD patterns on the surface of the sphere provides an elegant method of revealing information from these rich sources of crystallographic data.

cond-mat.mtrl-sci↗

arXiv2019

Advances in electron backscatter diffraction

We present a few recent developments in the field of electron backscatter diffraction (EBSD). We highlight how open source algorithms and open data formats can be used to rapidly to develop microstructural insight of materials. We include use of AstroEBSD for single pixel based EBSD mapping and conventional orientation mapping; followed by an unsupervised machine learning approach using principal component analysis and multivariate statistics combined with a refined template matching method to rapidly index orientation data with high precision. Next, we compare a diffraction pattern captured using direct electron detector with a dynamical simulation and project this to create a high quality experimental "reference diffraction sphere". Finally, we classify phases using supervised machine learning with transfer learning and a convolutional neural network.

physics.comp-ph↗

arXiv2019

Indexing Electron Backscatter Diffraction Patterns with a Refined Template Matching Approach

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 α-iron sample. The drastic speed up and pattern refinement approaches should increase the widespread utility of pattern matching approaches.

cond-mat.mtrl-sci↗

arXiv2018

The effect of cooling rate and grain size on hydride formation in Zircaloy-4

We explore the distribution, morphology and structure of zirconium hydrides formed using different cooling rates through the solid state Zr+[H] --> Zr + hydride transus, in fine and blocky alpha Zircaloy-4. We observe that cooling rate and grain size control the phase and distribution of hydrides. The blocky alpha (coarse grain, > 200 micrometer) Zircaloy-4, has a smaller grain boundary area to grain volume ratio and this significantly affects nucleation and growth of hydrides as compared to fine grain size (~11 micrometer) material.

cond-mat.mtrl-sci↗

arXiv2018

AstroEBSD: exploring new space in pattern indexing with methods launched from an astronomical approach

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.

physics.comp-ph↗