My NiTi alloy samples have two phases (martensite and austenite) with strong texture. The volume fraction of the phases need to be characterised in my research. But it is very difficult to get a expected result via XRD due to the overlaping diffraction peaks and strong texture of martensite and austenite. I know neutron diffraction and synchronous radiation XRD may be available. however, both of them are not realistic for me. So what method should I take to get it?
Hello
It is good to make micro-structures of the obtained materials. The crystallographic method can determine the quantities of phases.
Success in research.
Regards Emil Yankov
@Emil Yankov: Thank you for your advice. Could you recommend some relevant papers on crystallographic method to determine the quantities of phases? I have read about the literature on the determination of amorphous content by DSC. However, due to the existence of friction heat between lattices, the enthalpy of residual martensite transformation measured by DSC during heating is disturbed, especially for ultrafine grained materials.
Regards Zhongzheng Deng
Phases can be measured on microstructure samples on an Image Analyzer attached to a Metallurgical Microscope (Olympus Make).
Probably the easiest way is to analyze digital images of polished and etched surfaces using an image analysis software such as ImageJ, which can be downloaded for free from the NIH website.
Dear Zhongzheng Deng
you have a reasonable difficult problem. I agree with the already mentioned phase quantification, so you can safely calculate the individual volumes and then, the volume fraction. The sample preparation for such measurement is critical, once you need the overall description of each phase. Every sample preparation is a danger by itself, in some sense. You may impose phase transitions that you will only be aware afterwards. For grounding I suggest to do it in acetone, it will cool down as evaporation occurs, and you will have a reasonable temperature control. In your case, I don't believe acetone will promote some change over the sample. With fine powder, you increase the chance to have good characterization of your phases. Some peak overlaps are not so critical as seems, as far as some diagnostic peaks still not overlapped. As I never worked with this system, I don't know if you could try polarized light to have an evaluation of the relative quantities. Have a look, it may help you. One of the significant differences between the two phases is the crystal structure is that Martensite has a body-centered tetragonal (BCT) crystal structure, whereas austenite has a face-centered cubic (FCC) structure. The martensite phase growth requires very little thermal activation. It is a diffusioness transformation. Martensite has a lower density than austenite, so that the martensitic transformation results in a relative change of volume. Such difference in crystal structure may be enough to get a useful Rietveld fitting.
Best regards,
WNM
@Wagner Da Nova Mussel:
Dear Mussel,
Thank you for your kindness and detailed answers! I'm sorry. I didn't make question clear. The sample is a cold rolled NiTi alloy; it has two phases (co-martensite and austenite) with strong texture.
Best regards,
Zhongzheng Deng
@Deshpande;@DeFord
Dear Deshpande and DeFord,
Thank you for your answers! I'm sorry to not give a clear decscription of my question. The sample is a cold rolled NiTi sheet. So its grain size is very small. Metallurgical Microscope is not applicable. Perhaps TEM can be used. However, TEM only reflects the local situation, because of the limitation of the field of vision. Nevertheless, if there is no better alternatives, it is still feasible. Thank you!
Best regards,
Zhongzheng Deng
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