Hydrodynamic multi-phase model for simulation of laser-induced non-equilibrium phase transformations

A hydrodynamic model based on transport equations and semi-empirical multiphase equations-of-state for metals is developed and applied to simulation of short pulse laser melting and resolidification. New computational algorithms are developed for modeling of two-phase zones of solid-liquid and liquid-gas coexistence, as well as for explicit tracking of interfaces between the phases. The model accounts for both heterogeneous and homogeneous melting mechanisms. A series of simulations are performed for bulk aluminum irradiated by a picosecond laser pulse at a wide range of laser fluence. The effect of non-equilibrium conditions and homogeneous melting on the melting/resolidification times and the maximum depth of melting is investigated. Three distinct stages are identified in the melting/resolidification process, namely, the fast homogeneous melting of the overheated surface region, a slower increase of the melting depth due to the advancement of the sharp melting front formed at the end of the homogeneous melting, and the reverse propagation of the liquid-crystal interface in recrystallization. Computational results are in a good qualitative agreement with the results of recent molecular dynamics simulations of laser melting.