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

Abstract

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. 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 is obtained, the crystal orientation with respect to a reference sample and detector orientation can be determined and presented. Unfortunately, because of challenges related to crystal symmetry, there are limited available pattern‐indexing approaches and this has probably hampered open development of the technique. In this article, a new method of pattern indexing is presented, based upon a method with which satellites locate themselves in the night sky, and its effectiveness is systematically demonstrated using dynamical simulations and real experimental patterns. The benefit of releasing this new algorithm as open‐source software is demonstrated when this indexing process is utilized, 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 toolkit, the authors hope to open up EBSD developments to more users. The software code and example data are released alongside this article for third party developments.

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

“…If we assume that we know, or can measure, the pattern centre with reasonable precision with standard methods (e.g. just using the 2D Radon based pattern centre measurements available within commercial or open-source software such as AstroEBSD [25]), then we can perform re-projection and gain reasonable indexing success which is demonstrated with the example iron data set shown with this work.…”

“…Once a certain number of bands has been detected in the Kikuchi pattern any of the well known indexing algorithms, e.g. [27,25], can be used for determining the corresponding orientation. In this section we utilise AstroEBSD [25] and analyse the error distribution of the resulting orientation determination method.…”

“…Britton et al [25] for conventional indexing using a planar Radon transform and the As- peaks were sought. The pattern centre was optimised by searching for the minimum weighted mean angular error using a 10 × 10 grid array.…”

Advancing characterisation with statistics from correlative electron diffraction and X-ray spectroscopy, in the scanning electron microscope

“…EBSD patterns for each point were processed in MATLAB, with background correction, radial cropping, and hot-pixel/split-chip fixes performed using the AstroEBSD package developed and presented by Britton et al previously [23]. EBSD patterns were originally captured with an aspect ratio of 4:3, but these were cropped to squares to simplify the refined template matching indexing (as discussed by Foden et al [12]) prior to creation of the data matrix.…”

Rapid electron backscatter diffraction mapping: Painting by numbers

“…This includes the 1% of points not assigned during the reconstruction step (black points in Figure 5 (c)), and points at twins and near grain boundaries which were assigned to regions but where the acquired pattern could not be indexed. (Bruker ESPRIT 2.1 [28] was used to index the conventional EBSD map, and AstroEBSD [32] was used to index the Rapid EBSD data.) Figure 5 (f) shows the result from spatially binning the conventional EBSD map, increasing the step size by 10× to 2 μm.…”