Non-isothermal phase-field model of molten pool dynamics coupled with thermocapillary effect and phase change in metal additive manufacturing

High-fidelity phase-field model (PFM) for molten pool dynamics in metal additive manufacturing (MAM) is highly required, which fully takes into account the coupled multi-physics problems of molten pool flows. Herein, we present a thermodynamically consistent non-isothermal PFM for incompressible multiphase flows with thermocapillary effects and phase change. The model is derived from a thermodynamic framework of incompressible two-phase flows, invoking the microforce theory and Coleman–Noll procedure. Features of molten pool flows, such as the large liquid–gas density ratio and temperature gradient, are fully taken into account. The model is further extended to the complicated thermo-solid–liquid–gas flows with laser-induced phase change (melting, solidification, and evaporation). Within the phase-field framework, we derive the smooth function for describing surface tension and recoil pressure acting on the molten pool and establish the thermodynamics of mass and energy losses due to evaporation. Several numerical benchmarks, such as flat gas–liquid interface, single bubble and droplet, and molten plate and particle, are introduced to validate the developed non-isothermal phase-field model. Simulation results show that the area of solidified single track is approximatively linear with the linear energy density. The non-isothermal PFM shows its ability to investigate the molten pool dynamics and pore defect formation during MAM process.