Abstract
Site preference and the effects of ternary additions (Mn, V, etc.) on the twin energy in γ-TiAl were studied by means of all-electron total energy self-consistent calculations based on the local density approximation. The results show that when Mn, Ti, or V substitute on the Al-sites in γ-TiAl, the twin energy is about 20–25% lower than that of stoichiometric γ-TiAl; this may explain observations of increased twinning activity in 48% Al TiAl. By contrast, when ternary additions of V (or Al) occupy Ti-sites, the twin energy has nearly the same value as that of pure γ-TiAl, which is consistent with the observation of only a few twins for Al-rich compositions. By comparing the total energy of Ti6(XAl5) and (Ti5X)Al6 supercells, it is found that the relative stability of Ti6(XAl5) over (Ti5X)Al6 (i.e., the preference for occupying Al-sites) is increased in going from Nb, V, Cr, and Ti to Mn, in agreement with observation that excess Ti occupies Al-sites, and Nb preferentially substitutes on the Ti-sites. The results indicate that Mn preferentially substitutes on the Al-sites, and V (or Cr) may occupy both Ti- and Al-sites.
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We have not shown the counterpart of partial DOS for Ti6(Al5 V); as a whole it has a similar feature as Ti6(Al5Mn).
We chose the electronic structure of V substituted on Ti-sites to be considered, because our site preference calculations unambiguously showed that Mn occupies preferentially on Al-sites.
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Xu, Jh., Freeman, A.J. Effects of ternary additions on the twin energy and site preference in γ-TiAl. Journal of Materials Research 9, 1755–1760 (1994). https://doi.org/10.1557/JMR.1994.1755
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DOI: https://doi.org/10.1557/JMR.1994.1755