Interstitial helium diffusion mechanisms in 〈1 1 0〉 tilt grain boundaries in BCC FeCr alloys: A atomistic study

In this work, we studied the migration of He in different 〈1 1 0〉 tilt grain boundaries (GBs) (Σ19{3 3 1}, Σ9{2 2 1}, Σ3{1 1 1}, Σ3{1 1 2}, Σ11{1 1 3}, Σ9{1 1 4}) in Fe–(5,10,14)Cr random alloys, with the misorientation angle varying in the range 26°–141°. We performed systematic molecular statics and molecular dynamics simulations to characterize the interaction of He with the core of the GBs and to estimate the diffusion coefficient, migration mechanism, and effective core migration energy. The simulations were performed in the 600–1400 K temperature range, applying a set of interatomic potentials for Fe–Cr–He system recently proposed by Juslin et al., specially fitted to the properties of He in bulk Fe. We found that the migration of an interstitial He near the core of the Σ3{1 1 2} GB is essentially three-dimensional (3D) within the investigated temperature range. The transition of diffusion mode from one-dimensional (1D) to 3D was observed in other GBs in the studied alloys. The results clearly demonstrate, that the accommodation, migration mechanism, and diffusivity of He is extremely sensitive to variations in atomic structure of a particular GB.