Femtosecond laser melting NbMoTaW refractory high entropy alloy: A micro-scale thermodynamic simulation

Refractory high entropy alloys (RHEA) exhibit excellent material properties, such as high strength, high hardness, high melting point and high temperature oxidation resistance. Ultrafast laser fabricating RHEAs is potential widely used in extreme environments at high temperature. In the present study, a multiscale simulation of the femtosecond laser pulse melting NbMoTaW RHEA film was performed to observe the transient interaction process between femtosecond laser and RHEA at the atomic scale. The temperature dependent electron thermophysical parameters (electron heat capacity, electron thermal conductivity and effective electron–phonon coupling factor) were calculated from density functional theory. The two temperature model coupling molecular dynamics was used to reveal the temperature change, the density variation and the pressure evolution during the interaction of a single pulse laser with the NbMoTaW RHEA. The simulated ablation and melting depths varied differently with laser fluence parameters. The ablation depth increases with the laser fluence, while the non-removed melting depth varies little with laser energy beyond the ablation threshold. The research reveals the mechanisms in melting process at atomic-level, and the results are helpful to the fabrication of RHEA.