An integrated Eulerian-Lagrangian-Eulerian investigation of coaxial gas-powder flow and intensified particle-melt interaction in directed energy deposition process

Abstract In this work, a comprehensive framework consisting of coaxial gas-powder flow and melt-flow dynamics models is developed for the laser-assisted directed energy deposition process. Firstly, by using the coupled Eulerian-Lagrangian models, the dynamics of the carrier-shielding gases, the particle-stream trajectory, and the in-flight temperature rise of the powder-particles are predicted. This is done by solving the momentum transfer equations, the k-e turbulence equations, the discrete phase equation and the energy equation. Thereafter, using the particle-stream characteristics above the melt-pool free-surface, an interface-tracking melt thermo-hydrodynamics model is developed in an open-source environment to track the incident powder-particles in the melt-pool. Using the developed framework, the spatial and temporal variation of the melt-pool morphology due to the powder-particle impingement is analyzed. The computational results of particles-melt interaction show an erratic flow pattern with an oscillatory behavior of the melt-pool free-surface. The incident powder-particle creates a crater on the free-surface of the melt-pool and generates a radially outward strong ripple-wave. The velocity field of the melt-pool shows a highly non-linear behavior which is extremely sensitive to the particle impact. It was found that the thermo-capillary stresses dominate only at the instances when there is no particle insertion and the flow is stabilized. Using the solidification parameters obtained from the melt-pool dynamics model, the influence of the fluctuating thermo-fluidic field on the resultant columnar dendritic microstructure is studied. The comparison of the numerically predicted deposition dimensions and the dendritic arm spacings shows a good correlation with the corresponding experimentally measured values from the in-house controlled experiments.