Role of impurities in the formation of point defects in Ti-Al alloys

The effect of impurities on the point defect formation energies in Ti-Al alloys was studied by the projector augmented-wave method. The grand canonical formalism was applied to calculate the formation energies of several kinds of defects. It was shown that the formation energy of Al-vacancy decreases by similar to 1.3 eV with increasing its content in the series of alloys Ti3Al-TiAl-TiAl3, whereas the formation energy of Ti-vacancy changes insignificantly. In general, the formation of Ti-vacancies is more preferred in Ti-Al alloys rather than the formation of Al-vacancies. We demonstrate that Nb, Mo, Tc, Ru, Rh, Pd lead to increase of the formation energy of Al-vacancy if they occupy the Al sites, whereas only Mo and Tc increase the formation energy of Ti-vacancy. All 4d elements, if they substitute for Ti, reduce the formation energies of Al-vacancy. The influence of impurities on elastic constants is discussed.