Energetics of helium-vacancy complexes in Fe-9Cr alloys from first-principles calculations

Abstract

The formation of helium-vacancy complexes under irradiation is crucial for the nucleation and early-stage growth of helium bubbles in reduced activation steels. The energetics of HenVm (V represents vacancy) complexes (n and m = 0–4) in Fe-9Cr alloy models and bcc Fe were investigated by first-principles calculations. A stronger self-trapping of He in Fe-9Cr alloys than in bcc Fe is found. The existence of Cr suppresses multiple He trapping in the vacancy to some extent. Besides, alloying element Cr strengthens lattice expansion induced by He atoms. Lower formation energy of HenVm complexes and stronger binding of a He atom to HenVm complexes in Fe-9Cr alloys as compared to in bcc Fe indicate that density of these small complexes can be higher in alloys. When m/n > 1, aggregation of a vacancy to HenVm complexes becomes more difficult in Fe-9Cr alloys than in bcc Fe. It is well known that the irradiation induced void swelling is related to the aggregation of small vacancy clusters or HenVm complexes. The results indicate that the addition of Cr atoms to the Fe matrix is beneficial to the irradiation swelling resistance aided by dispersed HeV complexes.