A full non-equilibrium partial solute drag model for rapid solidification of a binary alloy: modeling and verification

Rapid solidification technologies have driven imperative need for highly accurate kinetic models for migration of non-equilibrium solid/liquid ( S / L ) interface. Existing models, however, are unable to simultaneously address two critical issues, i.e., the non-equilibrium solute diffusion effect in the bulk phases and the solute drag effect influencing both interface migration and trans-interface diffusion at the interface. By employing the thermodynamic extremal principle (TEP) to self-consistently handle the dependent dissipation processes and their constraints, this study developed a full non-equilibrium partial solute drag (FNE-PSD) model for rapid solidification of a binary alloy, which integrates the above two issues into a unified description. To validate the current FNE-PSD model, molecular dynamics simulation was performed for the Ni-30 at.%Cu alloy and the key kinetic parameters in the composition and velocity response functions were derived directly without introducing any preset parameter. Results showed that the FNE-PSD model accurately captures the sharp transition to complete solute trapping (CST) as the interface velocity reaches the solute diffusion velocity in the liquid. Compared with the recent local non-equilibrium partial solute drag (LNE-PSD) model, the current FNE-PSD model could successfully predict the solute drag dependent solute trapping behavior from the case without solute drag to the case with full solute drag. The current work indicates the TEP might provide a robust framework that is critical to advancing modelling non-equilibrium kinetics and controlling non-equilibrium processing.