Investigation of Particle-Melt Pool Impact Dynamics and In-Flight Laser-Powder Stream Coupling in Laser Directed Energy Deposition

This study aims to advance the fundamental understanding of key phenomena in the Laser Directed Energy Deposition (L-DED) process, with a focus on laser beam shadowing, attenuation, and particle–melt pool interactions. Using in-house high-speed visible imaging and photodiode systems, we investigated laser, powder stream, and melt pool interactions. High-speed in-situ synchrotron X-ray radiography was performed at the P61A Beamline at PETRA III, DESY Hamburg, with a custom L-DED setup to investigate particle impingement and dissolution dynamics. Systems studied included metal–metal combinations (Ti6Al4V in Ti6Al4V, 316L SS in Ti6Al4V, and Cu in Ti6Al4V) and a ceramic–metal case (WC in Ti6Al4V). Additionally, multiphysics modeling with a coupled CFD-DEM framework and photon discretization was performed. Our integrated in-situ experiments and modeling provided unprecedented insights into: (1) particle-melt pool surface penetration dynamics and the influence of Marangoni convection-driven motion within the melt pool, (2) highly oscillatory and chaotic melt flow from high-speed particle impacts, (3) increased velocities of partially vaporized particles due to recoil pressure, leading to deep craters in the melt pool, and (4) inflight laser-particle interactions significantly altering the laser beam, introducing stochasticity and randomness. These findings advance fundamental understanding of the L-DED process and offer pathways for optimization and control.