The microstructures of Ti-Al alloys in the range 56–62 at.% Al have been studied. These compounds consist of a basic L10 structure on which is superimposed an irrational modulation (Ti3Al5 related). This is incommensurate by occupation. It has two-dimensional modulations in which the wave vectors are q1 = α(a* + b*) and q2 = α(-a* + b*) where a* and b* are the L10 reciprocal basis and α is an irrational fraction. α decreases from 0.282 to 0.26 as the Al concentration increases to 60 at.% Al, i.e., the positions of the satellites change continuously with varying Al concentration. A third phase, TiAl2, appears at a composition of 62 at.% Al which means that no Ti3Al5 (62.5 at.% Al) of stoichiometric composition can ever exist.
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This work is supported by the Engineering and Physical Sciences Research Council (Contract number GR/L 79960/01)
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Wang, S., Fort, D., Jones, I.P. et al. Incommensurate Structure in Al-rich TiAl Alloys. MRS Online Proceedings Library 646, 413–418 (2000). https://doi.org/10.1557/PROC-646-N5.43.1