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Tips & Tricks: Why you should save EBSD patterns

In traditional electron backscatter diffraction (EBSD) mapping, EBSD patterns are acquired and subsequently analyzed using a Hough transform to determine the diffraction band positions to calculate the crystallographic orientation using a list of candidate phases. The determined orientation and phase are recorded, along with other metrics, including the EBSD image quality value, the confidence index of the orientation solution, and the scanning electron microscope (SEM) image intensity. This reduction of the data is efficient for generating different maps, charts, and texture plots within the OIM Analysis™ Software and does not require the EBSD patterns to be saved after the initial indexing. However, recent and continuing developments have resulted in new applications where the saved EBSD patterns can be used to extract more information than was previously available. This article will review some of the ways in which saved EBSD patterns can be used to enhance EBSD analysis.

The most straightforward application for using saved EBSD patterns is reviewing patterns after collection. In OIM Analysis, this can be done using FlexiView, where the EBSD patterns can be dynamically displayed from every point within the collected map, along with the calculated crystallographic unit cell and the pole figure. This feature is used to verify that recognizable EBSD patterns were obtained and identify any visual differences in pattern quality or intensity.

Saved patterns can also be used with EDAX’s PRIAS™ imaging technology. With PRIAS, different regions of interest (ROIs) are defined within the EBSD image. These ROIs are then used as electron imaging detectors while the area of interest is scanned with the electron beam. Different imaging contrast mechanisms are active depending on the ROI's position. During EBSD mapping, PRIAS ROIs are predefined. PRIAS can also be used with saved patterns. The ROIs can be more freely positioned and adjusted for optimized contrast and imaging quality. Figure 1 shows PRIAS images from a nickel superalloy from an ROI positioned in the center of the detector screen (Figure 1a) and from an ROI positioned at the bottom of the screen (Figure 1b). These images visualize the gamma/gamma prime microstructure with complementary contrasts between the two PRIAS images.

PRIAS images from a nickel superalloy from left) an ROI positioned in the center of the detector screen and right) an ROI positioned at the bottom of the screen.
Figure 1. PRIAS images from a nickel superalloy from a) an ROI positioned in the center of the detector screen and b) an ROI positioned at the bottom of the screen.


In some instances, quality EBSD patterns are captured, but the indexing quality is low. With saved EBSD patterns, it is easy to identify the root cause of this indexing performance, and many alternatives for improving indexing are available. The band detection results can be displayed with the saved pattern and adjusted for improved performance if necessary. This is not possible without saved EBSD patterns. Additional phases can also be added to the list of candidate phases. These additional phases can be verified with saved EBSD patterns and, if successful, can be used to analyze the entire dataset using the indexing functionality with OIM Analysis. These indexing tools allow users to reindex the entire dataset or to target the reindexing user-defined partitions for more efficient analysis. For example, users may reindex only the points with a low initial confidence index.

For multi-phase samples, it can sometimes be difficult to correctly apply an EBSD background correction using a single background signal because the average atomic number of the phases can vary significantly. This results in a difference between the EBSD signal and the background signal, which can degrade band detection and indexing performance. With saved EBSD patterns, phase-specific backgrounds can be generated and used to improve performance regardless of the number of phases present.

Indexing results can also be improved by using EDAX’s patented NPAR™ processing with saved EBSD patterns. With NPAR, each individual pattern is averaged with its neighboring patterns to improve the resulting average pattern’s signal-to-noise ratio (SNR). This SNR improvement, in turn, improves band detection and pattern indexing performance. While comparable with traditional frame averaging during EBSD mapping, NPAR improves SNR and indexing while providing faster acquisition rates on the SEM. NPAR typically provides indexing improvements on almost all microstructures, provided that the sampling step size is smaller than the feature sizes of interest.

The OIM Matrix™ module has been recently added to the OIM Analysis software. OIM Matrix compares experimental patterns with dynamically simulated patterns to determine the best-fit crystallographic orientation and phase. There are two approaches for this type of indexing. The first is dictionary indexing, where a library of simulated EBSD patterns is calculated before indexing the pattern. The second is spherical indexing, where the experimental pattern is projected onto the spherical master pattern to find the best fit over the simulation. Spherical indexing is new in OIM Analysis v9.

Shows a screenshot of the Scan Details window within APEX.
Figure 2. Shows a screenshot of the Scan Details window within APEX.


One final application of saved EBSD patterns is HR-EBSD or high-angular resolution EBSD. This approach selects a reference pattern from each grain in the measured microstructure. Other patterns within the grain are compared and correlated against the grain reference pattern. This technique measures elastic strain in materials and improves angular precision.

This article summarizes the many applications for using saved EBSD patterns to enhance EBSD analysis. From a practical perspective, the option to save EBSD patterns is selected when defining an EBSD scan in the APEX™ Software. Figure 2 shows a screenshot of the Scan Details window within APEX. In this window, the option to Save Patterns is shown. When saving patterns, users can save as 8-bit up1 files or 16-bit up2 files. These patterns are saved with the same filename as the scan file and must be in the same folder when opening within OIM Analysis for further analysis.