Spatiotemporal insights into the femtosecond laser homogeneous and heterogeneous melting aluminum by atomistic-continuum modeling

The homogeneous and heterogeneous melting phenomena of Al film irradiated by the femtosecond laser are studied by coupling the molecular dynamics simulation with the two-temperature model. The embedded-atom method potential is implemented to simulate the interaction among atoms. The validation of this model is carried out by showing the agreement between numerically calculated melting phenomena and experimental results. It was found that for the target material with a thickness of 133.4nm irradiated by the femtosecond laser with 200fs duration and 150J/m2 absorbed fluence, the melting process has gone through two stages. The rapid melting stage dominated by homogeneous melting occurs within the first 2ps and it is followed by the slow melting stage dominated by heterogeneous melting within 20ps. The molten aluminum gradually develops an interface between the liquid zone and the melting zone after 20ps. The regions with higher electron-phonon coupling strength correspond to the two types of melting regions. The size of the two melting zones can be controlled by the electron-phonon coupling factor and electron thermal conductivity, where the latter can even determine the conversion between ablation and melting phenomena. In addition, the peak points and the curve evolution found in the lattice temperature spatial distribution curves show the state of the melting process. These results not only verify the existence of a controllable influence mechanism of temperature, thermophysical parameters, and melting phenomena, but also contribute to additive manufacturing, fine control of melting area and type, and other femtosecond laser-induced metal-related manufacturing applications.