Measurement of geometrically necessary dislocation density with high resolution electron backscatter diffraction: Effects of detector binning and step size

Recent advances using cross-correlation analysis of full resolution high quality electron backscatter diffraction (EBSD) patterns have provided a method for quantitatively mapping the stored dislocation density at high spatial resolution. Larger areas could be mapped with image binning or coarser step sizes. We have studied the effects of image binning and step size on the recovery of GND density. Our results suggest that: (i) the measured lower bound GND density noise floor broadly agrees with Wilkinson and Randman’s 2009 prediction, where a decrease in step size or an increase in misorientation uncertainty increases the noise floor; (ii) increasing the step size results in a lower GND density being recovered as some dislocations are now considered as statistically stored dislocations (SSDs); (iii) in deformed samples the average GND density stays relatively constant as the degree of pattern binning is increased up to 8×8. Pattern binning thus provides a means of increasing the data acquisition and analysis rate without unduly degrading the data quality.

► Recovery of GND content using HR-EBSD was studied with differing CCD binning and sample step size.
► Increased binning results in poorer recovery of the stored GND density using Nye's analysis.
► High level of binning may be acceptable for severely deformed samples.
► Reduction in step size results in an increase in the measurement noise.
► Reduction in step size also leads to separation of dislocations into GNDs and SSDs.