MODELING OF NONEQUILIBRIUM SURFACE MELTING AND RESOLIDIFICATION FOR PURE METALS AND BINARY-ALLOYS

A model was developed for surface melting and resolidification of both pure metal and binary alloy substates. Nonequilibrium kinetics are in troduced in the model to account for the departure from thermodynamic equilibrium at the solid/liquid interface. The modeled problem involve s a moving boundary with both heat and solute diffusion and is solved by an implicit control volume integral method with solid/liquid interf ace immobilization by coordinate transformation. To illustrate the mod el capabilities, we have analyzed laser-induced surface melting of pur e metals (Al,Cu, Ni, Ti) and dilute Al-Cu alloys, and some typical res ults are presented. The computation results show some large solid over heating and melt undercooling effects, which result from the high heat flux and the slow kinetics. Large interface velocity variations are a lso seen during the process, depending on he substrate material and la ser flux. Complex interface velocity variations during the earlier sta ges of resolidification were also predicted for the alloys, and result from interactions between the several physical mechanisms involved. R esults on interface temperatures, solute concentrations, and nonequili brium partition coefficients are also presented.