Site preferences and formation energies of substitutional Si, Nb, Mo, Ta, and W solid solutions inL10Ti-Al

Abstract

Modifications to alloy chemistry are often used to tailor the intrinsic flow behavior of structural materials. Models of solution strengthening, high-temperature yield stress and creep must relate the effects of chemistry to the mechanisms which influence these material properties. In ordered alloys, additional information regarding the crystallographic site occupancy of substitutional solid solutions is required. The energy of intrinsic and substitutional point defects in ${L1}_{0}$ TiAl are calculated within a first principles, local density functional theory framework. We calculate the relaxed structures and energies of vacancies, antisites, and substitutional defects using a plane-wave pseudopotential method. The results of these total energy calculations are incorporated into a simple thermodynamic model in order to determine the density of point defects as a function of temperature and stoichiometry. Defect densities are presented as a function of alloy chemistry and temperature for binary TiAl and ternary additions (Si, Nb, Mo, Ta, and W). Defect formation energies are calculated using the derived chemical potentials of each atomic species for several alloy compositions. The predicted site selection of the solutes are in excellent agreement with recent x-ray emission experiments using a quantitative statistical method for atom location by channelling enhanced microanalysis.