Interatomic potentials for atomistic simulations of the Ti-Al system

Abstract

Semiempirical interatomic potentials have been developed for Al, $\ensuremath{\alpha}\ensuremath{-}\mathrm{Ti},$ and $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ within the embedded atom method (EAM) formalism by fitting to a large database of experimental as well as ab initio data. The ab initio calculations were performed by the linearized augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, and planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide a reasonable description of the lattice thermal expansion, demonstrating their usefulness for molecular-dynamics and Monte Carlo simulations at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ calculated with the EAM potential is in fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ is an antisite disorder compound, in agreement with experimental data.