A widely spread prejudice is that EBSD is inferior to X-ray diffraction in the analysis representativeness. Meanwhile EBSD areas of millimeter sizes (with a properly increased scanning step of course) seems to comply with limitations due to the beam divergence and the detector dimensions. That is already comparable to XRD !
However I could not find specific size limitations in the user guides. Please shine some light on this issue, if possible. May it be, say, 3 mm?
It depends on several things, we have done (single) scans of up to 10mm in size. With stitching (automatically moving the stage and make many scans), you can go much larger. A problem with the huge scans is the significant spatial distortions, particularly the trapezium distortion. Also, the pattern center shift correction needs to be properly calibrated for these large scans, to avoid misindexing at the edges.
It will be different from one to another microscope-EBSD detector configuration. You need to tilt the sample to 70 deg and take a sharp image with low magnification. Especially far from the center, the image becomes blurred. Using a very large working distance will help. However, it would help if you also had a good signal in EBSD detector. So you would need to have your EBSD detector mounted or moved down to larger working distances (Bruker and Oxford detectors can be moved in the chamber easily). In a single scan, 3 mm is possible (please find map attached with ~2.7 mm width). If you combine beam and stage scan (which is now automated in EBSD software), you can do as much as you need (the SEM I'm using allows traveling 50 mm in each direction) or do the whole sample. (second image attached). With a speed of 4000 patterns per second, the map with the whole sample was scanned in 20-30 minutes.
Thanks a lot, colleagues!
Let alone stitching option (moving stage), it is still desirable to realize to which degree the orientation accuracy degrades at the periphery of different single scans, for example those of 3 or 5 mm. As you guess, my question concerns the texture analysis. Dear Grzegorz, cuold you please Give me the bibl. reference, if any, to your 3 mm scan.
This was just map done last week. In the reference below you can see another 4x3 mm map of single crystal (fig.2 and 5) and evidence that error caused by the size of the scan can be with advanced calibration of the geometry followed by orientation refinement reduced to less than 0.15 degree:
https://www.mdpi.com/1996-1944/13/12/2816
Thank you very much, it is just what I wanted. By the way, we are also going to estimate errors depending on the single area dimensions on a perfect single crystal standard. Interesting, whether you experimentally estimated such errors on common metals rather rather than an etalon?
It was performed on Si because it was easiest to perform. Wafers are flat plane parallel and give good quality patterns straight from the box. Large common metals single crystals are soft and EBSD sample prep could cause some deformation. It is doable by electropolishing for example. We just didn't need it.
What about the following alternative?
At any (e.g. martensite) common steel you mark some area of few grains and then scan it at different stage positions separated by a millimetre scale gap. Of course, the section plane should be kept.
Thus you can compare two local pole figures of the same domain, each containing a low number of reflection points.
It is doable but doesn't seem to be like any real-life EBSD measurement. It will be hard to see on the pole figure if we have an error of 0.2 degree. If you need it I can make such measurements in my spare time.
If you prefer, you can wait a little until we try it with a Si etalon and then STEEL on our Lira SEM. Anyway it is planned and I will let you know what happened finally.
Yet, it would be interesting to compare performances of two SEMs In this respect.
To supplement my last remark... errors of 0.2 deg do not matter for pole figures since any characteristic texture component comprises a notably wider angular domain. Of course, this error becomes significant when imaging weak interfaces of the microstructure. However it is another hystory to be further addressed with appropriate means.
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