Microstructure Detail Extraction via EBSD: An Overview

Abstract

Automated electron back-scatter diffraction (EBSD) techniques have been available for almost 20 years. They are routinely used for surface characterization of crystalline samples for the determination of lattice orientation, phase and overall texture. To a lesser extent, geometrically necessary dislocation (GND) content has been extracted from the local orientation gradient (curvature), and some efforts have been made to determine elastic strain. However, recent advances in crosscorrelation techniques for determining distortion between EBSD patterns have led to new possibilities for detail extraction. Not only can orientation information be ascertained at much higher resolution compared with traditional EBSD, but GND content can now be determined with improved precision, and elastic strain can be acquired with higher confidence. This chapter will review the microstructure information that can be recovered from both legacy EBSD and the more recent high-resolution EBSD (HREBSD) frameworks. Introduction to Traditional EBSDEBSD techniques analyze back-scatter diffraction patterns for information regarding atomic lattice structure. In a typical setup a polished crystalline sample is held at a tilt of 70 • from horizontal under an electron beam of a scanning electron microscope (SEM) with energy in the range 5-30 keV. 405Strain and Dislocation Gradients from Diffraction Downloaded from www.worldscientific.com by PURDUE UNIVERSITY on 04/12/15. For personal use only.

Nucleation and propagation of {101¯2} twins in AZ31 magnesium alloy

“…Using high-resolution electron backscatter diffraction (HREBSD) techniques, near-surface GND tensors can be recovered from lattice distortion measurements. The principles and methods for determining GND density and resolving these values onto individual slip systems are described in [21,[32][33][34], building upon work by Nye and Kr‫‬ሷ ner [35,36].…”

Validation of kinematically simulated pattern HR-EBSD for measuring absolute strains and lattice tetragonality

“…The basic idea of HR-EBSD is to determine the distortion that must be applied to a reference structure in order to arrive at the local structure under consideration by comparing the EBSD patterns of the two structures using cross-correlation techniques [17]. Regions of interest (ROIs) are defined in the two images, and cross correlations are applied using fast Fourier transforms (FFT) to determine the shifts that must be made to the reference ROI to line up with the ROI of the image being analyzed (Fig.1).…”

“…The underlying equations are similar to those used by the CrossCourt software tested in [16], as described in [7]. Landon / Kacher removed a small approximation from the equations, resulting in a slightly different set of equations [17]; however this has a smaller effect than the method of applying the traction-free boundary conditions in the software when tested on simulated patterns of randomly deformed lattices. The traction-free boundary conditions are required to enable determination of the hydrostatic components of lattice distortion, which cannot be resolved by considering only the pattern shifts in the cross correlation method.…”

Influence of Noise-Generating Factors on Cross-Correlation Electron Backscatter Diffraction (EBSD) Measurement of Geometrically Necessary Dislocations (GNDs)

“…Poisson noise was added to the pattern to reflect noise in electron interactions and camera electronics, in line with previous studies of noise in EBSPs (Cizmar et al, 2008; Pinard et al, 2011; Park et al, 2013; Wright et al, 2015). Although others have cited Poisson noise as a representative noise type for some factors in the imaging process, its application to specific aspects in EBSD imaging within this paper have been inferred based on statements in the referenced papers.…”