Hi everybody,
I have a problem in obtaining EBSD images and determining an accurate martensite area fraction for superelastic NiTi.
I have the lattice parameters for my NiTi specimens and have modified the EBSD files for NiTi in the austenite and martensite phases. However, since the XRD scans did not clearly show the lattice parameters for the martensitic phase, I used the reported values in the literature, where the austenite lattice parameters were exactly equal to my specimens.
Even with these modifications, the EBSD scans did not identify the amount of martensitic phase in my specimens. I know that there is a large amount of martensite in the specimen since the optical microscope image showed that.
I was wondering if anyone might know whether there is a specific setting or input that I may be missing in my EBSD scans that I am not obtaining the correct martensitic area fraction or if my situation is a common issue for NiTi.
Thank you,
Hi,
I had diffuculties with martensite and EBSD, too. In my opinion it depends more on the system (SEM used) and the preparation. I learned that I need to scan really small parts, so the martensite needles will be detected. And I needed to use a FE cathode. With a LaB6 there was almost no chance to get the patterns right.
At the end, I used TEM samples (punched out and electrolytical polished) for EBSD measurements. Thats a pitty because you only get really small maps, but in that case I got nice EBSD maps and a good solution of the martensite needles.
I also found out, that I had a massive substructure in my samples that made it difficult to scan and solve larger maps.
A suggestion for you: scan same small maps to show your martensite and use another measuring system, e.g. XRD or magnetic measurements, to determine the amount of martensite and austenite. That way it works quite well.
Best regards,
Jasmin
Dear Mohammad:
Nitinol is very difficult to polish for examination of the structure and more challenging for EBSD work. I have attached a short pdf on specimen prep of nitinol. On my web site (punch my name into Google) you will see more on preparation for EBSD (and many other topics); a 2 part paper on the overall topic is also attached. The specimen MUST be kept as flat as possible for EBSD, so electropolishing will not help. Good luck!
George Vander Voort
Dear George,
Very informative and useful articles.
Thank you very much,
Mohammad
Mohammad:
Good luck with your research work. Several articles and talks were published/given in 2009 claiming that most of the published LOM microstructural work on Nitinol were artifacts. One individual claimed that my Nomarski DIC image of the martensite formed by going through the SME was a stain! I've never seen a 3-dimensional stain in 50 years doing metallography work! I got my annealed Nitinol samples from a prominent professor in Germany and he said that my images were perfect! But, a group in Jena, Germany, claimed that numerous publications show artifact structures, including mine, but they have never shown what they claim is the true structure after going through the SME! All they have shown are TEM images (I never saw a single LOM microstructure in any of their publications) of artifacts that they created! So, be careful reviewing the literature on this issue.
George Vander Voort
Dear George Sir,
Very much thank you for valuable information.
I am trying to get EBSD image from past one year but i could not accomplish.
After reading your paper i will restart ...If i accomplish the whole credit goes to you only sir.
Thank You
Surla Ramesh
Dear George,
Thanks for sharing the documents related to NiTi preparation for EBSD. A force of 150 N is said to be needed for grinding and polishing in the table (Nitinol_Prep and Etch.pdf). Is this large force correct? and what is the Red lubricant?
Best,
Morteza
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