Ab initio calculations are implemented to investigate the structural and helium diffusion behaviour in Fe 6.25 at.% Cr binary alloys based on FCC–Fe. Our simulation results confirmed that the increase of Cr contents in the AFM phase is beneficial to strengthen the shear deformation resistance and hardness of the alloys, and also leads to greater lattice distortion. The presence of Cr atoms accelerates the migration of mono-helium atoms between tetrahedral and octahedral gaps in varying...