  The addition of alloying elements plays an essential role in helium (He)
behaviours produced by transmutation in metal alloys. Effects of solutes (Ni,
Cr, Ti, P, Si, C) on the behaviours of He and He-He pair in face-centred cube
(fcc) iron have been investigated using first-principles calculations based on
density functional theory (DFT). For the interactions of solutes and He, we
found that Ti, P, Si, and C attracts He is more potent than Ni and Cr in fcc
iron. We have determined the most stable configuration for the He-He pair,
which is the Hesub-Hetetra pair with a binding energy of 1.60 eV. In
considering the effect of solutes on the stability of the He-He pair, we have
proposed a unique definition of binding energy. By applying the definition, we
suggest that Ti and P could weaken He self-trapping, and Cr and C are
beneficial for He self-trapping, while Ni is similar to the matrix Fe itself.
For the diffusion of He, which is the necessary process of forming the He
bubble, we determined that the most stable interstitial He is in a tetrahedral
site and could migrate with the energy barrier of 0.16 eV in pure fcc iron. We
further found that Ti and Si can increase the barrier to 0.18 and 0.20 eV; on
the contrary, Cr and P decrease the barrier to 0.10 and 0.06 eV, respectively.
Summarizing the calculations, we conclude that Ti decreases while Cr increases
the diffusion and self-trapping of He in fcc iron.
