Modeling of nonequilibrium surface elting and resolidification for pure metals and binary alloys

A model was developed for surface melting and resolidification of both pure metal and binary alloy substrates. Nonequilibrium kinetics are introduced in the model to account for the departure from thermodynamic equilibrium at the solid˜liquid inter-.face. The modeled problem involves a moving boundary with both heat and solute diffusion and is solved by an implicit control volume integral method with solid/liquid interface immobilization by coordinate transformation. To illustrate the model capabilities, we have analyzed laser-induced surface melting of pure metals (Al, Cu, Ni, Ti) and dilute A l-Cu alloys, and some typical results are presented. The computation results show some large solid overheating and melt undercooling effects, which result from the high heat flux and the slow kinetics. Large interface velocity variations are also seen during the process, depending on the substrate material and laser flux. Complex interface velocity variations during the earlier stages of resolidification were also predicted for the alloys, and result from interactions between the several physical mechanisms involved. Results on interface temperatures, solute concentrations, and nonequilibrium partition coefficients are also presented.