Abstract
We performed molecular dynamics simulations based on density functional theory to systematically investigate the Fe–Ni–C system including (1) pure Fe and Ni; (2) binary Fe–Ni, Fe–C, and Ni–C; and (3) ternary Fe–Ni–C liquid compositions at 3000 K and three simulation volumes corresponding to pressure ( P ) up to 83 GPa. Liquid structural properties, including coordination numbers, are analyzed using partial radial distribution functions. Self-diffusion coefficients are determined based on the atomic trajectories and the asymptotic slope of the time-dependent mean-square displacement. The results indicate that the average interatomic distance between two Fe atoms ( r Fe–Fe ) decreases with P and is sensitive to Ni ( X Ni ) and C ( X C ) concentration, although the effects are opposite: r Fe–Fe decreases with increasing X Ni , but increases with increasing X C . Average r Fe–C and r Ni–C values also decrease with increasing X Ni and generally remain constant between the two lowest P points, corresponding to a coordination change of carbon from ~ 6.8 to ~ 8.0, and then decrease with additional P once the coordination change is complete. Carbon clustering occurs in both binary (especially Ni–C) and ternary compositions with short-range r C-C values (~ 1.29 to ~ 1.57 Å), typical for r C-C in diamond and graphite. The self-diffusion results are generally consistent with high- P diffusion data extrapolated from experiments conducted at lower temperature ( T ). A subset of additional simulations was conducted at 1675 and 2350 K to estimate the effect of T on diffusion, yielding an activation enthalpy of ~ 53 kJ/mol and activation volume of ~ 0.5 cm 3 /mol.