The elastic behaviors and theoretical tensile strength of γ-TiAl alloy from the first principles calculations

The temperature dependent elastic modulus and theoretical tensile strength have been investigated by the first-principles calculations to get insight into the mechanical performance of γ-TiAl in the case of high temperature and impurity. The phase stability of γ-TiAl at elevated temperature has been proved by calculating the phonon dispersion relations and elastic constants. The elastic modulus B, G and E decrease linearly by 8%, 22%, and 20% respectively with the temperature increasing from 0 K to 850 K. The reduction of B is small, indicating that the resistance to external pressure for γ-TiAl is still superior at high temperature. The reduced G/B ratio of 0.488 endows γ-TiAl fairly good ductility at elevated temperature. The tensile test shows that the ideal tensile strength is somewhat reduced due to the presence of impurity (C, O, P, and S) in comparison with pure γ-TiAl. Compared to C, P, and S, the O impurities are more easily trapped in γ-TiAl matrix with largely negative formation energy. For the γ-TiAl compound, the values of theoretical tensile strength corresponding to the first phonon instability are 16.1 GPa, 5.3 GPa, 6.3 GPa, and 14.6 GPa along [100], [001], [110], and [111] directions, respectively. For TiAl-O system, we obtained the values of 15.1 GPa, 10.8 GPa, 6.4 GPa, and 13.3 GPa, respectively.