Journal
ACTA MATERIALIA
Volume 191, Issue -, Pages 131-148Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2020.03.026
Keywords
HR-EBSD; HR-TKD; On-axis TKD; Digital Image Correlation; Geometrically necessary dislocations
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Digital image correlation (DIC) techniques usually performed on deforming speckle patterns are applied here on electron diffraction patterns (EDP) in order to map disorientations with high angular resolution, as well as geometrically necessary dislocation densities and elastic strains. The proposed approach relies on a DIC analysis which is conducted independently from the microscope calibration. It registers EDP as a whole through a single and large region of interest whose relative deformation with respect to a reference EDP is described by a first-order homography. Subpixel registration is performed iteratively in the spatial domain using an inverse-compositional Gauss-Newton (IC-GN) algorithm which integrates the correction of the optical distortions. Its robustness against large orientation changes as well as its computational efficiency are improved by mean of an automated and path-independent initial guess which fairly captures the effects of large rotations on the EDP. Using successive Fourier-Mellin and Fourier transforms based cross-correlation techniques, the initial guess measures the in-plane rotation and translation between the reference and the target EDP, respectively. The performances of the technique are illustrated in markedly plastically deformed steels using two electron diffraction techniques in the scanning electron microscope. A 15% deformed interstitial free steel is investigated by means of electron backscattered diffraction (EBSD) while a quenched and tempered oxide dispersed strengthened steel subjected to martensitic transformation is characterized using a recently developed on-axis Transmission Kikuchi Diffraction (TKD) configuration. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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