Molecular dynamics simulation of the structure and surface tension of Fe–C and Fe–N binary melts

Abstract This study employs molecular dynamics simulations to investigate the structural characteristics and surface tension behaviors of Fe–C and Fe–N melts at various compositions and temperatures. Through analysis of atomic distributions, radial distribution functions (RDF), and coordination numbers, we reveal key relationships between atomic behavior and surface phenomena. Our findings indicate that the enrichment of C and N at the melt surface, along with the contraction of Fe atoms into the liquid phase, results in density and pressure gradients that influence surface tension. Increased C and N concentrations enhance surface enrichment and intensify Fe contraction. Notably, the first peak heights of RDF for Fe–C and C–C pairs, as well as Fe–N and N–N pairs, show opposing trends with rising concentrations, reflecting competition between these atomic species. In the Fe–C system, surface tension steadily decreases, while the Fe–N system experiences an initial increase in surface tension before peaking at 0.2 wt% N and then declining. As temperature increases, surface tension decreases, accompanied by a weakening of short-range order. These insights enhance our understanding of the impact of C and N enrichment on Fe-based melts.