Exploration of the coupled lattice Boltzmann model based on a multiphase field model: A study of the solid-liquid-gas interaction mechanism in the solidification process

A multiphase field model coupled with a lattice Boltzmann (PF-LBM) model is proposed to simulate the distribution mechanism of bubbles and solutes at the solid-liquid interface, the interaction between dendrites and bubbles, and the effects of different temperatures, anisotropic strengths and tilting angles on the solidified organization of the SCN-0.24wt.% butanedinitrile alloy during the solidification process. The model adopts a multiphase field model to simulate the growth of dendrites, calculates the growth motions of dendrites based on the interfacial solute equilibrium; and adopts a lattice Boltzmann model (LBM) based on the Shan-Chen multiphase flow to simulate the growth and motions of bubbles in the liquid phase, which includes the interaction between solid-liquid-gas phases. The simulation results show that during the directional growth of columnar dendrites, bubbles first precipitate out slowly at the very bottom of the dendrites, and then rise up due to the different solid-liquid densities and pressure differences. The bubbles will interact with the dendrite in the process of flow migration, such as extrusion, overflow, fusion and disappearance. In the case of wide gaps in the dendrite channels, bubbles will fuse to form larger irregular bubbles, and in the case of dense channels, bubbles will deform due to the extrusion of dendrites. In the simulated region, as the dendrites converge and diverge, the bubbles precipitate out of the dendrites by compression and diffusion, which also causes physical phenomena such as fusion and spillage of the bubbles. These results reveal the physical mechanisms of bubble nucleation, growth and kinematic evolution during solidification and interaction with dendrite growth.