The Effect of Pattern Quality on Measurements of Stress Heterogeneity and Geometrically Necessary Dislocation Density by High-Angular Resolution Electron Backscatter Diffraction

Abstract

We examine the effect of pattern quality on the output of high-angular resolution electron backscatter diffraction (HR-EBSD) analyses. Band contrast, as a proxy for pattern quality, was varied by adjusting the number of frames averaged per electron backscatter pattern during data collection. The same region in a deformed sample of the mineral olivine was mapped six times varying the number of frames averaged between 1 and 30 between each map. Each data set was analyzed with HR-EBSD, producing maps of intragranular stress heterogeneity and geometrically necessary dislocation (GND) density. As the number of frames averaged increased, the noise in stress and GND calculations decreased, revealing more substructure in the mapped region. The worst pixels, with low band contrast, are the most improved by increased frame averaging, whereas those with high band contrast are largely unaffected. Additionally, the probability distribution of stresses narrows as high-stress noise is reduced with increased pattern quality, which also affects estimates of dislocation density from statistical analysis of the stress distributions. As regions with high stress and/or high GND density are typically of interest in HR-EBSD maps and are often associated with low band contrast, frame averaging may be used as a tool to improve the quality of these analyses. Most importantly, however, is that comparisons are made between HR-EBSD datasets with similar mean band contrast to ensure that observed differences are microstructural in origin and not an artefact of data collection.