Effects of SEM Distortions on EBSD Grain Size Measurements

Systematic discrepancies persist between results from grain size measurement standards, such as ASTM E 112 and ASTM E 2627, when different imaging techniques and analysis methods are used. The source of these discrepancies may be differences in imaging physics, resolution limits, grain boundary definitions, post-processing practices, or combinations thereof. Geometric distortions and drift effects in scanning electron microscope imaging are systematically modeled using synthetic microstructures to assess their impact on electron backscatter diffraction-based grain size measurement accuracy. Standard methods are compared to a lesser-known method, the Triple Point Count (TPC). Most distortion types introduce smaller biases than the expected accuracy of the methods under typical imaging conditions. TPC provides consistent performance across varying resolutions and sampling conditions. This provides further evidence that reported discrepancies are largely driven by an assumption made in the estimate for converting intercept measurements to ASTM grain size numbers, as recently reported by Evans et al.