Density Functional Theory (DFT) has been used to investigate ordering phase transformations in a Ti-Al-Mo model alloy system. Specially, we focused on two ordered phases, cubic o and hexagonal 02 with nominal compositions Ti0:5Al0:5, and their two disordered counterparts, and 0. In the present work, we report on the structural and elastic properties of the = o and 0= 02 phases, while replacing both Al and Ti with Mo. Our results suggest that the energy of formation decreases with increasing Mo content when Al is replaced by Mo in all phases. The lattice parameters slightly decrease as a function of Mo content when placed on the Ti sub-lattice of the o. Moreover, our calculations reveal a structural instability of the o with respect to the ground state -TiAl phase; the ordered o phase becomes stable only for Mo content of 16.at% and more. Based on the energies of formation the fully ordered phases are found to be more preferable than the disordered phases.
The Young's moduli of both the cubic as well as the hexagonal phases soften slightly with increasing Mo content. Finally, we will compare our rst principles predictions with experimental data based on synchrotron measurements. 1
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