Determining dislocation cell sizes for high‐strain deformation microstructures using the EBSP technique

Abstract

SummaryThe effect of several data collection and processing choices has been examined for high-resolution electron back-scatter pattern (EBSP) investigation of a highly deformed sample. The results were compared with a transmission electron microscope (TEM) investigation of the same sample. The estimated dislocation cell size was examined as a function of data cleaning strategy, line intercept vs. reconstruction method, critical misorientation angle definition and step-size. The best agreement with the TEM results was obtained using a modified relative reconstruction algorithm on fine step-size maps allowing some of the noise in the data to be overcome.Step sizes of up to one-quarter the average cell size yielded similar values for the estimated average cell size. As a result of the mixture of both high-and low-angle boundaries, single diffraction condition TEM images may give larger cell size estimates than the EBSP data. Orientation noise in the EBSP data, however, still limits the extent to which quantitative information can be extracted.

Deformation Mechanism of Zr702 Processed by Equal Channel Angular Pressing

“…The average size of cells measured by TEM is smaller than that measured by EBSD, which is perhaps due to the limited angular resolution of the latter. Because the angular resolution in EBSD is about 2 deg, [25,[34][35][36] the boundaries of lower angular separation tend to be ignored. As is indicated by the selected area diffraction (SAD) pattern in Figure 7(a), the grain shown in the general area of the bright-field micrograph contains only two crystal orientations, which implies that single pass is insufficient to refine the grain structure.…”

“…For the measurement of the spacing of GNBs and the size of dislocation cell, the line intercept scans with a boundary misorientation definition of 3 and 2 deg, respectively, were used, while the average misorientation was calculated using a 2 deg lower cutoff to reduce the noise of data. [34][35][36] The size of a cell was defined as the equal circle diameter (D ECD ) calculated directly from the measurement of the cell areas. Thin foils for transmission electron microscopy (TEM) were cut from the middle part of extruded rods and were prepared by a twin jet polisher at -50°C and 25 V for 60 seconds using a solution consisting of perchloric acid:methanol of 5:95 in the volume ratio.…”

Austenite Stability and Its Effect on the Ductility of the Cold-rolled Medium-Mn Steel

“…Due to the misorientation resolution limitation of EBSD, only the grain boundaries with misorientation angle larger than 2° were given in the EBSD maps. 22) The samples for SEM were treated by means of cold grinding and polishing, corrosion for 15 s with 3% nitric acid alcohol solution, and microstructure observation was conducted in S-4300 cold field emission scanning electron microscopy (SEM). The stress strain curves at different temperature were analyzed to understand the work hardening mechanism of steel during deformation process.…”

Annealing Behavior of Nanostructured Aluminum Produced by Cold Rolling to Ultrahigh Strains

“…Measurements of d ECD are particularly sensitive to artifacts of small crystallites of just a few pixels that arise as a result of noise in the orientation data. Therefore, a modified reconstruction method has been used [24] in which the value of d ECD is calculated ignoring all crystallites of size less or equal to 3 map pixels. The fraction of high-angle boundaries and the average misorientation angle have also been calculated considering only misorientations of angle greater than 2 deg, i.e., f HAB = N >15 deg /N >2 deg , where N >15 deg and N >2 deg are the number of misorientations greater than 15 and 2 deg, respectively.…”

“…In order to examine the microstructural data in a quantitative manner, the following procedure was adopted. For each map a modified reconstruction method [24] was first used to find each crystallite using a boundary misorientation definition of 2 deg, ignoring all features detected by the software of area less than or equal to 3 map pixels. The physical size corresponding to this three-pixel cutoff is a function of the EBSD map step size, which was taken in the range 0.1 to 0.3 lm for deformed samples and 1 to 2 lm for samples annealed at 300°C and above.…”