EBSD-ImageNote
Further explanations and examples in a recently published article in the Microscopy & Microanalysis journal: pdf | bib
If you're wondering how does EBSD work, then you've come to the right place. EBSD, or Electron Backscatter Diffraction, is a method of resolving the crystal orientation and microstructure of a solid. In addition, EBSD can be used to reconstruct diffraction patterns and to perform simulations of microstructures.
Electron Backscatter Diffraction (EBSD) is a microstructural characterisation technique. It measures diffraction patterns in a specimen and provides information on crystal orientation. The patterns are indexed and used to build crystal orientation maps. EBSD complements conventional analysis techniques. EBSD is also a useful tool for phase discrimination. However, it is not as accurate as electron diffraction in the transmission electron microscope.
A typical EBSD dataset includes the distribution of phases, nature of boundaries, and other additional information. This information can be used to calculate the ODF unambiguously and to interpret it when considered in the usual 3D Cartesian representation. Several sophisticated software packages are available to present these data.
An orientation map is a visual representation of the crystallographic microstructure. It is constructed based on the EBSP pattern. The pattern includes features that represent the reflectance peaks, such as the Orientation Density Function (ODF) and pole figures. Moreover, low-level features such as edges and blobs can also be identified. In addition to providing insight into the phase distribution, EBSD maps can help to identify grain size, grain boundary structure, and morphology.
Crystallographic orientation is defined by three Euler angles. These angles bring the crystal coordinate system onto the specimen coordinate system. Each of the angles represents an angle between lattice planes. By subtracting these angles, the resulting angle is represented by the band/plane that intersects.
EBSD is a fast and efficient way of acquiring data. The spatial resolution of EBSD can be as high as several microns. Depending on the accelerating voltage and the size of the sample, this resolution may vary. On the other hand, the field of view is limited. Therefore, this technique is most suitable for small area specimens.
EBSD can be used to identify crystal orientation in opaque or opaque-to-transparent phases. However, many dispersed phases cannot be characterized by EBSD. EBSD is not as accurate as XRD, which provides detailed information about crystallographic texture. Some advanced analysis tools can also be used to extract information on elastic strains, residual stresses, and dislocations.
EBSD can also be combined with energy dispersive spectroscopy (EDS) to detect a wide range of structural parameters. EBSD is a valuable complement to other analysis techniques, as it is a reliable and accurate method of measuring orientation.
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Electron backscatter diffraction (EBSD) is a powerful analytical tool used to characterize crystallographic microstructures. It gathers statistical data on grain size, texture and grain boundary character. The method has been applied to a wide range of materials. These include metals, semiconductors, and minerals. EBSD has been used to study residual strain distribution in welding joints, deformed materials, iron oxide layers on steel, and tissue morphology.
The technique can be performed on multiphase materials, such as metal thin films. However, it is best suited for HTSc materials. This is because the simplest phase index is online. XRD is usually used to measure texture, but it does not have the ability to accurately distinguish different phases.
Unlike XRD, the EBSD system is fully automated. In addition, it has a very high spatial resolution. When used in combination with ion beam bombardment, it can be used to characterize microstructures of complex material structures.
Depending on the type of material studied, the EBSD system can have a lateral resolution of up to 10 nm. However, the EBSD resolution depends on the quality of the recorded EBSD patterns.
Typically, the EBSD procedure uses a camera positioned 20 mm from the sample. The pattern is measured at a rate of 65 to 70 patterns per second. A camera controller is needed to control the camera. An electron image drift correction program is also required.
The EBSD maps provide information on local deformation of crystallographic microstructures. They can be displayed as a 111 pole figure or as a positional distribution of orientations. Colors in the map correspond to the poles of the inverse pole figure. EBSD maps can be compared with a 3D EBSD-based orientation microscopy system, which extends the 2-dimensional features of EBSD by providing the crystallographic indices of interface planes.
The EBSD system has its strengths in the precise definition of the microstructure. Moreover, rudimentary software is available for 3D data analysis. Although some limitations exist, these problems are largely solvable.
For example, the optimum specimen volume is limited to 50 x 50 x 50 um3. But if the specimen is too small, it may be difficult to obtain a satisfactory diffraction pattern. Another limitation is the requirement for high tilt of the specimen.
Electron Back-Scatter Diffraction is a powerful technique for studying crystalline microstructures. It can be used to determine the morphology, size and orientation of grains and crystals. EBSD also provides a high degree of spatial resolution.
EBSD can be used to measure residual stresses in semi-conductors and determine the rotation angle of ductile materials. Unlike other diffraction techniques, EBSD is nondestructive and can be performed at very low acceleration voltages. In addition, it can be combined with other techniques, including X-ray spectroscopy and WDX. EBSD is also an excellent method for observing serial sections.
EBSD can be used to study both crystalline and deformed material structures. It can be applied to an enormous variety of materials problems. For example, it can be used to investigate the size, texture and crystal structure of metals and alloys.
EBSD has been widely used in the materials community. It is particularly useful for mapping the crystallographic orientation of large areas. Compared to TEM diffraction techniques, EBSD can provide a more accurate picture of the local crystal structure. EBSD can also provide quantitative information on the crystallographic textures of different phases. Combined with other methods, it can also be used to characterize the size and morphology of individual grains.
Generally, the effective angle of incidence for an EBSD measurement is a result of a combination of the stage position, the specimen tilt, and the beam's y-movement. However, slight variations in surface normals can change the effective angle of incidence. This can lead to distorted orientation maps. Using the correct reference system can help overcome this problem.
In order to obtain good diffraction patterns from a sample, it is necessary to prepare the surface well. These processes can be performed on a variety of materials, including glass, ceramics and metals. A milled surface is particularly advantageous. If the surface is amorphous, a low-kV ion polishing can be performed to remove the amorphous layer. Alternatively, the surface can be electropolished. The resulting flat surface is suitable for EBSD.
In order to perform a full indexing of EBSD data, the complete crystallographic information should be recorded. Complete indexing is then performed off-line from recorded Hough-peak and Nye-peak data.
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Reconstruction of electron backscatter diffraction (EBSD) data for microstructure simulations requires the segmentation of grains into voxels. The number of voxels required to reconstruct the EBSD data for a microstructure is a function of the misorientation tolerance and the total number of voxels recorded. It is important to select the proper misorientation tolerance and grain size to ensure the quality of the reconstruction.
In general, grain-level metrics tend to have opposite trends with increasing misorientation tolerance. Increasing the tolerance also tends to increase the number of grains that merge. For a well recrystallized material, a misorientation tolerance of about 5.0 is sufficient. However, a larger misorientation tolerance allows for grains to be merged even in deformed materials.
One technique for reconstructing EBSD data for microstructure simulations is to use connected component analysis. This allows individual features to be identified individually, which in turn allows for more reasonable grain morphologies to be established.
Another method is to perform EBSD pattern cross correlation. This is a technique that has been used to achieve more accurate lattice rotation. By applying this technique, the lattice rotation can be determined from the Hough transforms of patterns.
Using a combination of these methods, a sample of EBM Inconel 718 was characterized. A 50-mm-thick build layer was used for this study. 204 slices were collected over three days. Data were recorded at a rate of 65-70 patterns per second.
The size of observable volumes can be as small as 50 x 50 x 50 nm3. To calculate the observable volume, the pattern indexing is performed off-line from the recorded Hough-peak data. The total number of voxels in the EBSD data was then measured to obtain a confidence index.
An optimized reconstruction was performed to retain a high fraction of masked voxels with a high confidence index. Using the EBSD data, the diffraction pattern was reanalysed using a software package called AZtecCrystal. AZtecCrystal is designed to be simple and intuitive for new users.
AZtecCrystal includes a comprehensive set of tools for processing and analyzing EBSD patterns. The tool has been developed for advanced operators, yet is easy to use for newcomers.
© Copyright 2011, Philippe T. Pinard. Created using Sphinx 1.1.3.