Numerical investigation of interfacial dynamics for the melt pool of Ti-6Al-4V powders under a selective laser

The complex evolution of a melt pool of Ti-6Al-4V powder particles under a moving selective laser was studied numerically. A laser power of 175 W and scanning speeds of 850, 1250, and 1650 mm/s were used. An effective laser source term with a time-varying maximum intensity was applied to a representative cross section to simplify the three-dimensional problem into a two-dimensional computational domain. The numerical results were validated using experimental observations. The effects of surface tension, Marangoni, and recoil forces on the interfacial morphology were investigated numerically. For a scanning speed of 1250 mm/s, the Marangoni effect initially begins to pull the interfacial melting flow from the laser focus region to the lateral powder. Meanwhile, the accumulated laser energy leads to evaporation, producing a corresponding recoil force. The transport phenomena caused by the Marangoni effect and the inward recoil force contribute to the local suppression of the melt pool. The Marangoni flow conveys the laser energy to the lateral powder, which significantly enhances the wetting phenomenon. In the next stage, the surface tension force gradually becomes dominant, eliminating the local suppression and concave curvature. The interfacial curvatures in this stage overshoot when they change signs. This tendency results in a periodic sloshing motion and oscillation of the melt pool. This study provides a thorough understanding of the wetting and morphology of the melt pool from a microscopic viewpoint, which could result in detailed design guidelines.