Abstract: Fusion-based metal additive manufacturing (AM) relies on layer-by-layer deposition and rapid solidification, where the material transitions swiftly from liquid to solid. A key phenomenon during this process is solute trapping, a nonequilibrium effect governed by a velocity-dependent partition coefficient, which critically influences microstructure kinetics, morphology, and phase formation. In this study, we employ a recently proposed quantitative phase field (PF) model to systematically explore solute trapping, solute drag, and their impacts on pattern formation during rapid solidification at AM-relevant velocities, in both one and two dimensions. Our simulations reveal a growth mode transition from planar to cellular to dendritic, and back to cellular and planar, consistent with classical solidification theory. Based on PF simulations, we construct a solidification microstructure selection map and compare the primary dendritic/cell spacing with theoretical models. The simulated morphologies and arm spacing align well with experimental observations for Al-4Si and Ti-20Nb alloys under rapid solidification conditions. These findings highlight the potential of the PF model for predicting and controlling microstructure formation in the melt pool of AM processes, offering insights for optimizing AM fabrication.

Key words: Solute trapping, Solute drag, Rapid solidification, Phase field model, Additive manufacturing