Theoretical study of atomic transp ort via interstitials in dilute Fe-P alloys
Résumé
By combining Density Functional Theory, empirical potential and atomic transport model approaches, we investigate the energetics and the diffusion properties of P interstitials in dilute Fe-P alloys. Although P is a substitutional impurity in -iron, when a self-interstitial atom (SIA) approaches a substitutional P, the P atom becomes interstitial with an energy gain up to 1.0 eV. The octahedral and the 110 mixed dumbbell are the lowest energy configurations with similar stabilities. The P atoms are highly mobile in both configurations. The transitions between these two configurations also require low activation energies. The most likely mechanisms leading to long distance diffusion of an P interstitial are proposed by ab initio calculations. The resulting effective diffusion energy estimated by the transport model is 0.19 eV, which agrees with the result from the resistivity recovery experiments suggesting that the Fe-P mixed dumbbells are more mobile than the SIAs. The fast migrating P interstitial can be deeply trapped by a substitutional P. The resulting complexes are very stable with a binding energy of around 1.0 eV. Their mobility are investigated by means of the dimer method with the EAM Fe-P potential. Comparison between present predictions and existing experimental results are also discussed.