Interplay Between Oxygen-Dependent Marangoni Convection and Recoil Pressure in Laser Powder Bed Fusion of Ti-15Zr Alloys

Ti-15Zr alloys offer favorable biocompatibility, and interstitial oxygen provides an attractive pathway for further strengthening. However, the interaction between oxygen-modified Marangoni convection and evaporation-induced recoil pressure during laser powder bed fusion (LPBF) remains insufficiently understood. A three-dimensional multiphysics thermal-fluid model incorporating recoil pressure and temperature- and oxygen-dependent surface tension was developed. Surface-tension-only, recoil-pressure-only, and coupled simulations were compared on an idealized solid substrate, followed by discrete powder-bed simulations. Increasing oxygen content shifts the dominant Marangoni flow from outward spreading to inward convergence. Recoil pressure primarily drives central depression, whereas Marangoni convection redistributes molten metal. In transverse sections, low-oxygen outward flow competes with recoil-driven downward transport and promotes lateral spreading, whereas high-oxygen inward flow reinforces downward circulation. In longitudinal sections, reversed Marangoni flow suppresses recoil-driven rearward transport and promotes recirculation behind the vapor depression. Increasing oxygen content from 0 to 1.0 wt.% raises the top-view projected-area fraction with <!-- MathType@Translator@5@5@MathML2 (no namespace).tdl@MathML 2.0 (no namespace)@ -->