Influence of carbon on the kinetics of He migration and clustering in α-Fe from first principles

Density functional theory (DFT) calculations have been performed to study the interaction of carbon with He-vacancy complexes in α-Fe. Using the DFT predictions, a rate theory model that accounts for the evolution of carbon, helium, and defects created during irradiation has been developed to explore the influence of carbon on the kinetics of He diffusion and clustering after implantation in α-Fe. This DFT-based rate theory model predicts that carbon not only influences vacancy (V) migration but also He desorption, enhancing He mobility in particular for low V/C ratios. The reason for this behavior is mainly the formation of VC and VC2 complexes, which significantly reduces the mobility of vacancies with respect to pure Fe, inhibiting the formation of higher order clusters, i.e., HenVm, and increasing thus the number of He at substitutional positions at room temperature. Assuming reasonable values of carbon concentration, we successfully reproduce and interpret existing desorption experimental results, where all the energetic parameters for the relevant reactions were obtained from first-principles calculations. In addition, our study provides a detailed explanation of the various He migration mechanisms that prevail under the considered experimental conditions.