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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Electron backscatter diffraction | 6/7 | https://en.wikipedia.org/wiki/Electron_backscatter_diffraction | reference | science, encyclopedia | 2026-05-05T10:04:21.164305+00:00 | kb-cron |
=== The reference pattern problem === In HR-EBSD analysis, the lattice distortion field is calculated relative to a reference pattern or point (EBSP0) per grain in the map, and is dependent on the lattice distortion at the point. The lattice distortion field in each grain is measured with respect to this point; therefore, the absolute lattice distortion at the reference point (relative to the unstrained crystal) is excluded from the HR-EBSD elastic strain and rotation maps. This 'reference pattern problem' is similar to the 'd0 problem' in X-ray diffraction, and affects the nominal magnitude of HR-EBSD stress fields. However, selecting the reference pattern (EBSP0) plays a key role, as severely deformed EBSP0 adds phantom lattice distortions to the map values, thus, decreasing the measurement precision. The local lattice distortion at the EBSP0 influences the resultant HR-EBSD map, e.g., a reference pattern deformed in tension will directly reduce the HR-EBSD map tensile strain magnitude while indirectly influencing the other component magnitude and the strain's spatial distribution. Furthermore, the choice of EBSP0 slightly affects the GND density distribution and magnitude, and choosing a reference pattern with a higher GND density reduces the cross-correlation quality, changes the spatial distribution and induces more errors than choosing a reference pattern with high lattice distortion. Additionally, there is no apparent connection between EBSP0's IQ and EBSP0's local lattice distortion. The use of simulated reference patterns for absolute strain measurement is still an active area of research and scrutiny as difficulties arise from the variation of inelastic electron scattering with depth which limits the accuracy of dynamical diffraction simulation models, and imprecise determination of the pattern centre which leads to phantom strain components which cancel out when using experimentally acquired reference patterns. Other methods assumed that absolute strain at EBSP0 can be determined using crystal plasticity finite-element (CPFE) simulations, which then can be then combined with the HR-EBSD data (e.g., using linear 'top-up' method or displacement integration) to calculate the absolute lattice distortions. In addition, GND density estimation is nominally insensitive to (or negligibly dependent upon) EBSP0 choice, as only neighbour point-to-point differences in the lattice rotation maps are used for GND density calculation. However, this assumes that the absolute lattice distortion of EBSP0 only changes the relative lattice rotation map components by a constant value which vanishes during derivative operations, i.e., lattice distortion distribution is insensitive to EBSP0 choice.
=== Selecting a reference pattern === Criteria for EBSP0 selection can be one or a mixture of:
Selecting from points with low GND density or low Kernel average misorientation (KAM) based on the Hough measured local grain misorientations; Selecting from points with high image quality (IQ), which may have a low defect density within its electron interaction volume, is therefore assumed to be a low-strained region of a polycrystalline material. However, IQ does not carry a clear physical meaning, and the magnitudes of the measured relative lattice distortion are insensitive to the IQ of EBSP0; EBSP0 can also be manually selected to be far from potential stress concentrations such as grain boundaries, inclusions, or cracks using subjective criteria; Selecting an EBSP0 after examining the empirical relationship between the cross-correlation parameter and angular error, used in an iterative algorithm to identify the optimal reference pattern that maximises the precision of HR-EBSD. These criteria assume these parameters can indicate the strain conditions at the reference point, which can produce an accurate measurements of up to 3.2×10−4 elastic strain. However, experimental measurements point to the inaccuracy of HR-EBSD in determining the out-of-plane shear strain components distribution and magnitude.
== Applications == EBSD is used in a wide range of applications, including materials science and engineering, geology, and biological research. In materials science and engineering, EBSD is used to study the microstructure of metals, ceramics, and polymers, and to develop models of material behaviour. In geology, EBSD is used to study the crystallographic structure of minerals and rocks. In biological research, EBSD is used to study the microstructure of biological tissues and to investigate the structure of biological materials such as bone and teeth.
=== Scattered electron imaging ===
EBSD detectors can have forward scattered electron diodes (FSD) at the bottom, in the middle (MSD) and at the top of the detector. Forward-scattered electron (FSE) imaging involves collecting electrons scattered at small angles from the surface of a sample, which provides information about the surface topography and composition. The FSE signal is also sensitive to the crystallographic orientation of the sample. By analysing the intensity and contrast of the FSE signal, researchers can determine the crystallographic orientation of each pixel in the image. The FSE signal is typically collected simultaneously with the BSE signal in EBSD analysis. The BSE signal is sensitive to the average atomic number of the sample, and is used to generate an image of the surface topography and composition. The FSE signal is superimposed on the BSE image to provide information about the crystallographic orientation. Image generation has a lot of freedom when using the EBSD detector as an imaging device. An image created using a combination of diodes is called virtual or VFSD. It is possible to acquire images at a rate akin to slow scan imaging in the SEM by excessive binning of the EBSD CCD camera. It is possible to suppress or isolate the contrast of interest by creating composite images from simultaneously captured images, which offers a wide range of combinations for assessing various microstructure characteristics. Nevertheless, VFSD images do not include the quantitative information inherent to traditional EBSD maps; they simply offer representations of the microstructure.