Phase stability, mechanical, thermal, electronic properties, anisotropy, lattice dynamics and APB -energies of Ti2AlX intermetallics in α2, B2, and O phases: A first principle study

Abstract

The ternary titanium aluminide based alloys have been lucrative for high-temperature applications in next-generation aerospace vehicles. Present work systematically investigates phase stability, structural and elastic properties of Ti2AlX (X[dbnd]Mo, W, Ta, Nb, Zr, Hf) in α2, B2 and, O phases, calculated using density functional theory (DFT) within generalized gradient approximation (GGA). The Pugh's ratio, Poisson's ratio, Cauchy pressures, Vicker's hardness, machinability index, anisotropies, Debye temperature, thermal conductivity, melting temperature, and Peierls stress, derived from the elastic constants are also presented. Phonon calculations reveal that Ti2AlX (X[dbnd]Mo, W) in their α2 phase are dynamically unstable. The dominant slip systems are predicted from antiphase boundary (APB) energy calculations which indicate that dominance and mobility of the slip systems are largely affected by the ternary element ‘X′ and explains its ductile-brittle behavior. The bonding behavior is also investigated using the electronic density of states plots. The increased Ti-X bonding enhances while increased Ti-Al bonding degrades the ductility in Ti2AlX intermetallics.