Construction of Interatomic Potential for Fe–C Systems using Evolutionary Algorithm*

Due to the complexity of Fe-C bonding structure in iron alloys, to date, potentials have limitation on describing correctly either stable position of carbon or the diffusion barrier/pathway of carbon in BCC iron. Here, we developed an interatomic potential for Fe-C based on the bond-order framework and tested on diffusion of carbon in BCC iron. We found that, carbon diffuses from octahedral (O) site to the nearest neighbor O-site via tetrahedral (T) site with an energy barrier of 0.74eV, in agreement with experiment (O-site to O-site via T-site with energy barrier of about 0.81-0.87eV). Other theoretical works found similar diffusion mechanism with energy barrier of about 0.72-0.92eV. With this, we verified the transferability of the newly developed potential in the study of the effect of carbon on the BCC/FCC transformation in iron following the Bain mechanism. We found that the presence of carbon leads to the decrease of the BCC/FCC transformation energy barrier, consistent with our own first-principles calculations. Thus, the new potential can be a good candidate for modeling transformation processes in Fe-C.