Study on laser wire-filled welding process and microstructural behavior of TC4 titanium alloy

Laser wire-filled welding of TC4 titanium alloy involves complex thermal–fluid interactions and rapid phase transformations, which play a critical role in weld formation quality and microstructural evolution. In this study, a three-dimensional transient mathematical model is established based on the conservation equations of mass, momentum, and energy. The volume of fluid method is used to track the gas–liquid interface, and a rotating Gaussian volumetric heat source is adopted to accurately describe the laser energy input. Experimental results indicate that laser power has a significant influence on weld morphology, penetration depth, and defect formation. As the laser power increases from 2400 to 3000 W, the molten pool undergoes a transition from an unstable conduction mode to a stable regime and finally to an overheated state. An optimal laser power range of 2700–2800 W is identified, within which a uniform temperature field, stable molten pool flow, and defect-free welds are achieved. Microstructural analysis reveals that the fusion zone is mainly composed of coarse β columnar grains with intragranular martensitic α′, while equiaxed recrystallized grains are observed in the heat-affected zone; excessive laser power promotes the formation of Widmanstätten and bainitic structures. The numerical simulation results show good agreement with experimental observations, clarifying the intrinsic relationship between molten pool thermal–fluid behavior and microstructural evolution.