Boron and carbon solution and diffusion in iron: First-principles calculations and molecular dynamics simulation

The occupation and migration of boron (B) and carbon (C) in both body-centered cubic (BCC) iron and face-centered cubic (FCC) iron have been investigated using first-principles calculations. We examined the solution energies of all potential sites, including substitution sites (SS), octahedral sites (OIS) and tetrahedral sites (TIS) for B and C in BCC and FCC Fe. The site’s preference of an individual B/C atom in iron forms the following sequence: SS[Formula: see text] [Formula: see text] [Formula: see text]TIS[Formula: see text] [Formula: see text] [Formula: see text]OIS, for a B atom in BCC Fe; SS[Formula: see text] [Formula: see text] [Formula: see text]OIS[Formula: see text] [Formula: see text] [Formula: see text]TIS, for a B atom in FCC Fe; OIS[Formula: see text] [Formula: see text] [Formula: see text]TIS[Formula: see text] [Formula: see text] [Formula: see text]SS, for a C atom in BCC and FCC Fe. The optimal migration paths and the minimum diffusion energy barrier of B and C in both BCC and FCC iron have also been investigated. The migration path sequences are as follows: Tet 1 –Tet 2 and Oct 1 –Oct 2 for boron in BCC and FCC iron; Oct 1 –Tet–Oct 2 and Oct 1 –Oct 2 for carbon in BCC and FCC iron. The diffusion energy barriers are 0.87[Formula: see text]eV and 0.98[Formula: see text]eV for carbon and 0.89[Formula: see text]eV and 1.02[Formula: see text]eV for boron in BCC and FCC Fe. We found that much more energy is needed for B and C migrating in FCC Fe.