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Effects of ternary additions on the twin energy and site preference in γ-TiAl

Published online by Cambridge University Press:  03 March 2011

Jian-hua Xu  and
A.J. Freeman
Jian-hua Xu
Affiliation:
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208–3112
A.J. Freeman
Affiliation:
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208–3112 and Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439
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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.

Type
Articles
Information
Journal of Materials Research , Volume 9 , Issue 7 , July 1994 , pp. 1755 - 1760
Copyright
Copyright © Materials Research Society 1994

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References

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