Nonempirical prediction of impurity segregation in -Fe from first principles

Tsuru, Tomohito   ; Suzuki, Chikashi ; Kaji, Yoshiyuki  ; Tsukada, Takashi 

The segregation of impurities in -Fe were investigated by first principle density functional theory calculations. The segregation tendencies of various elements observed in reactor pressure vessels were considered and the interaction characteristics between Fe and each impurity element were estimated by mean field approximation. Stable -atom impurity clusters were subsequently chosen to evaluate the changes in free energy for clustering. These calculations show that Cu and Mn impurities embedded in -Fe are more stable when they are in the segregated state. Conversely, Nb and Ta are stable in the separately solute state. The present estimates provide reliable suggestions for the segregation characteristics. We suggest that the segregation tendency is derived from the -orbital interaction and that the solubility limit is not necessarily correlated with the tendency of clustering formation.