We all know both phase own hexagonal crystal unit cell, but alpha has hcp. Thus, I wonder whether the EBSD can tell the two phase apart? If we use the Ti-Hex in Oxford's software to identify one phase and get about 80% of alpha phase, is that result reliable?
Same crystal structure (HCP) and slightly different lattice parameters
Alpha: lattice parameters a = 0.5793 nm, c = 0.467 nm and c/a ratio of 0.80 Aluminide: lattice parameters a = 0.293nm, c = 0.467 nm and c/a ratio 1.59236
Dear D. Sornadurai,
Thank you for your answer. Can I understand it like that in your opinion the alpha prime has HCP crystal structure, similar with alpha phase in titanium, not the simple hexagonal structure. Meanwhile, I want to know when the crystal parameters change what's the difference between the Kikuchi patterns of theirs'. Is the difference large?
Thank you very much!
Chuanyun
Dear Velile Vilane ,
Thank you for your information about the crystal lattice of titanium. However, in your answer, I do not understand what the 'Alpha' stands for and what the 'Aluminide' stands for. Does the 'Alpha' means alpha phase in titanium alloy and the 'Aluminide' means intermetallics? If so, I find similar data ‘a=0.295nm c=0.468nm’ for alpha phase in titanium alloy in the book of 'Titanium 2nd edition'. I do not know why, can you explain your data?
Please check the following links and attachment:
http://contrails.iit.edu/DigitalCollection/1952/WADCTR52-335.pdf
https://etd.lib.metu.edu.tr/upload/3/12607260/index.pdf
http://www.icmp.lviv.ua/journal/zbirnyk.66/23601/art23601.pdf
www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA489602
Actually, since EBSD indexing system are mostly based on the angles formed by the Kikuchi paterns, EBSD is not efficient at identifying the lattice parameters.
For instance, different EBSD setting (e.g. WD in SEM) will result on different identified lattice parameters.
I suggest to use another technique, such as EDS/EDX for that purpose.
wo gan jue you qu xiang cha jiu neng yong EBSD jian ce chu lai. (hui da de NB ma?)
Normally, alpha and alpha prime phases can only coexist in (alpha + beta) type alloys (e.g. Ti-6Al-4V, Ti-6Al-2Sn-4Zr-6Mo) if the alloy is annealed below beta transus and above martensite start temperatures followed by water quenching. Due to element partitioning the lattice parameters of primary alpha and alpha prime (martensite) should differ as alpha prime is supersaturated in beta stabilising elements whereas alpha is not. Depending of the heat treatment temperature the amount of primary alpha might vary but I doubt that 80% primary alpha together with alpha prime can exist. To achieve 80% primary alpha the annealing temperature will definitively lay below martensite start, so no martensitic transformation of the remaining beta phase can be expected.
The only way to separate these phases by EBSD would be the definition of primary and alpha prime alpha (with exact lattice parameters), but I doubt that EBSD will be able to detect the different phases as their lattice parameters are close to each other, phases like Ti3Al or TiAl are irrelevant here…
If you only want to get the volume fractions of both phases (primary alpha and alpha prime), I would suggest a quantitative metallographic analysis in standard SEM as primary alpha will show equiaxed grains and martensite will show needles, separation by point grid will be possible.
I agree with Carsten Siemers.
Alpha and alpha' (martensite) have the same crystal structure (hcp type, SG P63/mmc) and unfortunately the variation of its lattice parameters with composition is usually very weak. That said it might be easier to use chemical methods (EDS etc.) instead of crystallography based techniques to find out whether the product is martensite or alpha.
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