Electron back scattered diffraction is a versatile tool for micro-structure and micro-texture analysis of a variety of materials e.g., metals/alloys, rocks, meteorites etc., EBSD completely works on crystallography where kikuchi patterns formed after diffraction from certain crystallographic planes are used to determine the orientation between grains, intra-granular misorientation, and orientation of phases. EBSD has also been used to detect, index and differentiate phases present in the materials. This detection has been based upon crystallographic aspects say, symmetry, point groups. In this respect, the above question automatically gets answered that BCT martensite and BCC ferrite should be distinguishable from each other. Now this poses another question, that EBSD should distinguish between FCC solid solution and an ordered FCC (L12) phase. Both have different crystal structures, space group (FCC: fm-3m, L12: pm-3m)?? Does it distinguish??
Regards
Subha Sanket Panda
PhD, IIT Kanpur
Subha Sanket Panda
Yes, Electron Backscatter Diffraction (EBSD) can distinguish between a face-centered cubic (FCC) solid solution and an ordered FCC (L1_2) phase, such as the case of differentiating between FCC austenite and ordered FCC L1_2 γ' phase.
The key reasons why EBSD can distinguish between these two phases are:
1. Crystallographic symmetry:
- FCC solid solution has the Fm-3m space group symmetry.
- Ordered FCC L1_2 phase has the Pm-3m space group symmetry.
- The different symmetries result in distinct Kikuchi patterns that can be used to index and differentiate the two phases.
2. Lattice parameter differences:
- FCC solid solution and ordered FCC L1_2 phase have slightly different lattice parameters, which can be detected by EBSD.
- This slight difference in lattice parameter is a result of the ordering of the atoms in the L1_2 structure.
3. Orientation relationship:
- The orientation relationship between the FCC solid solution and ordered FCC L1_2 phase is well-defined, and EBSD can detect this orientation relationship.
4. Phase contrast:
- EBSD can often detect the slight differences in image contrast between the FCC solid solution and ordered FCC L1_2 phase, which can aid in their differentiation.
So, in summary, the differences in crystallographic symmetry, lattice parameters, orientation relationships, and phase contrast allow EBSD to reliably distinguish between an FCC solid solution and an ordered FCC L1_2 phase, provided the data acquisition and analysis is done carefully.
It's worth noting that the ability to differentiate these phases also depends on factors like the quality of the EBSD data, the size and distribution of the phases, and the specific EBSD analysis techniques employed.
Hope it helps; partial credit AI
Thank you so much Dr. Mohammad Imam for the response. But, this has sparked some other queries !! First of all due to very small difference in the lattice parameters, very similar crystal structures, and possibly a coherent or semi-coherent relationship between these two (disordered FCC and ordered FCC: L12) in an orientation imaging micrographs they may appear indistinguishable. EBSD combined with EDS may help to differentiate in terms of chemistry or chemical composition, but the interaction volume of both are strikingly different. I hope you understand my queries. If you can answer it more clearly, that would help..
Regards
Subha Sanket
It is possible to distinguih BCT from BCC in steels. It is even possible to measure what is the c/a of BCT using EBSD. Please take a look at our papers:
Article Mapping of lattice distortion in martensitic steel—Compariso...
Article Tetragonality mapping of martensite in a high‑carbon steel by EBSD
Article Mapping of local lattice parameter ratios by projective Kiku...
Subha Sanket Panda answer given by Mohammad Imam is true only for AI he used. Practical EBSD is something different.
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