Solute trapping and solute drag during non-equilibrium solidification of Fe–Cr alloys

During additive manufacturing (AM), velocities of solid–liquid interfaces are on the order of 0 . 01 − 1 m⋅s −1 . Thus, local interfacial equilibrium may not be present. Molecular dynamics (MD) and Monte Carlo methods are employed to extract thermodynamic properties for a Fe–Cr binary alloy and the parameters that characterize the departure from interfacial equilibrium for velocities present during AM. The Gibbs free energies of the BCC, FCC, and liquid phases are determined and used in a partial-solute-drag model that self-consistently describes non-equilibrium solute trapping and solute-drag behavior. The partial-solute-drag model describes well the interfacial velocities as a function of supersaturation in the liquid and the velocity dependence of the partition coefficient. The maximum possible velocities, v 0 of the solid/liquid interfaces are determined, with v 0 of the stable BCC phase being higher than the metastable FCC phase, but both values are significantly lower than the reported speed of sound. Additionally, the partial-solute-drag model yields a trans-interface diffusivity much different from that of more classical models and very close to that measured in the MD simulations.