Suppressing peripheral flow collapse in WAAM through TiO₂-induced reversal of Marangoni stress: A thermal-fluidic mechanism and stability criterion

AbstractControlling molten pool free surface flow is essential for achieving geometric precision in wire arc additive manufacturing (WAAM) of aluminum alloys. Uncontrolled Marangoni convection and centrifugal forces often cause material waste and dimensional inaccuracy. To address this, we propose a surface tension regulation strategy by introducing TiO₂ particles into molten pool. A three-dimensional multiphysics model was developed to reveal the heat, forces, and fluid dynamics behavior in the molten pool. Experimental results showed that TiO₂ addition significantly improved manufacturing precision, reducing layer height deviation by 58.5% and increasing material utilization from 80.20% to 92.31% at a deposition rate of 604 cm3/h. Multiphysics simulation revealed that TiO₂ particles reversed Marangoni stress (Δσ from 0.1096 to −0.180 N/m), suppressing tangential flow velocity from 0.8 to 0.182 m/s. This reversal generated an inward normal stress of 127.75 Pa at the pool periphery, which exceeded the centrifugal force (34.56 Pa) and effectively counteracted flow collapse. Furthermore, a theoretical stability criterion (Lₘ ≥ L_f) was established, quantifying the critical surface tension threshold (Δσ ≤ −0.0537 N/m) for dimensional stability. This work provides valuable insights into surface active particle thermal-fluid control and offers a universally applicable criterion for high-quality, high-efficiency WAAM processes.