Dependence of measured crystal curvature on EBSD scanning step to derive density of statistically stored dislocations

The mapping of crystal curvature by the electron backscatter diffraction (EBSD) is conventionally used to image agglomerations of the Burgers vector (e. g., low-angle boundaries) in terms of geometrically necessary dislocations (GND). However, the concurrent curvature constituent due to statistically stored dislocations (SSD) still is not separated that remains a challenging problem because the material properties strongly depend on the proportion between GND and SSD densities. To get over this trouble, the present work analyzes the dependence of measured disorientations on the scanning step and thus determines its upper bound that mostly excludes the contribution of GND as manifested by strongly increased variations of measurement results. This way, a slope of the analyzed dependence within an admitted range of appropriately small steps enables determination of SSD density in terms of regular EBSD data. The latter avoids limitations of transmission electron microscopy (TEM) and X-ray diffraction (XRD) which usually apply to dissimilar scales and provide rather different estimates. For a case study, this approach is tested on lath-like and granular types of bainite in low carbon steel. Varying in the density proportion between coexisting bulk SSD and interfacial GND, such structures prove to be very suitable to verify performance of the proposed method.