Selective backscattered electron imaging of material and channeling contrast in microstructures of scale on low carbon steel controlled by accelerating voltage and take-off angle

Abstract

We studied the behaviors of contrast in backscattered electron (BSE) images of cross-sectional heattreated steel under various accelerating voltages and take-off angles. Changes in these conditions resulted in dramatic changes in contrast. Low accelerating voltage and low take-off angle improved the surface information and channeling contrast, whereas high accelerating voltage and high take-off angle enhanced the bulk information and reduced channeling contrast, resulting in improved Z̄ contrast. Such behavior can be understood by the ratio of low-loss electrons (LLEs), which are related to channeling contrast, to the inelastic BSE components detected. The distribution of these components varies with the accelerating voltage and take-off angle: the detection ratio of LLE to inelastic BSE increases with decreasing accelerating voltage and take-off angle. The results obtained in this study will be useful for obtaining Z̄ and crystallographic information separately in BSE images for the material of interest. © 2011 ISIJ.