EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Motivated by a recently reported martensitic transformation in the TiAl+Mointermetallic system, Density Functional Theory (DFT) has been used to investigate compositional trends in structural and mechanical properties of this model alloy system. Namely, two ordered phases, cubicβoand orthorhombicB19 (representing the fully ordered hexagonal phase), one hexagonal partially ordered phase,α′2, and two disordered phases,βandα′, all with nominal com-position Ti0.5Al0.5, were investigated. Mo was considered to replace either Alor Ti. To account for the chemical disorder, we applied a supercell approach employing so-called Special Quasi-random Structures and complemented it with calculations within the Coherent Potential Approximation in the framework of Exact Muffin-tin orbital theory. Our calculations reveal that Mo decreases the chemical stability of the TiAl+Mophases except for theβophase. Furthermore, the ordered phases are (as expected) chemically more preferable than the disordered ones at 0K, allowing for order-disorder transformations to happen at finite temperatures. Regard-ing the elastic properties, the βo with a low Mo content phase is mechanically unstable; all other phases are mechanically stable. Mo is predicted to increase ductility, stiffness (as measured by bulk modulus), and elastic anisotropy of the considered TiAl+Mo phases