Diffusion of Co and Ga in α-Ti

Abstract

The diffusion of Co and Ga atoms in α-Ti has been studied using the projector augmented-wave method in combination with the transition state theory. The formation energies of the interstitial and substitutional defects and the corresponding migration and activation energies along two crystallographic directions within the interstitial and vacancy diffusion mechanisms have been calculated. It has been shown that the energetically preferred interstice for the incorporation of both impurities is crowdion. In the case of Co, the formation energy of this defect is only 0.7 eV higher than that of the substitutional defect, while for Ga this difference reaches 2.6 eV. Using the Landman method and the eight-frequency model, the diffusion coefficients of Co and Ga have been calculated within both interstitial and vacancy mechanisms. It has been shown that Co diffusion occurs faster through the interstitials, while Ga diffuses within the vacancy mechanism. The migration and activation energies as well as diffusion coefficients and their anisotropy obtained in these cases are consistent with experimental data.