Abstract
Under the extreme fusion environment, helium impurities and vacancies play an important role in the microstructure evolution in Fe-9Cr based (wt.%) reduced activation ferritic/martensitic (RAFM) steels. In this work, vacancy and helium (He) impurity formation and related magnetism change in Fe-9Cr alloys are investigated by first-principles calculations. In Fe-9Cr alloys, Cr atom has an antiferromagnetic moment of around −1.85µB, as compared to that of Fe atoms in matrix. Contrary to the case for the first nearest neighboring (1nn) and 2nn Cr atom around Fe atom, 3–5nn Cr atoms increase the magnetic moment of Fe atom. The formation energy of vacancy and He impurities at various sites in Fe-9Cr are discussed. In Fe-9Cr alloys, He atoms at octahedral interstitial sites (O-sites) are unstable and eventually move to tetrahedral interstitial sites (T-sites) upon relaxation. The formation of defects can strongly affect the magnetic moment. T-site He atom leads to an obvious magnetic moment of 1nn Cr decrease. The electronic structure and local strain field analyses are performed to understand the origin of energy difference of He at different interstitial sites in Fe-9Cr alloys. The present theoretical results are helpful for a better understanding of the behavior of vacancy, He impurity and their complexes in Fe-9Cr alloys.
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