Numerical and experimental studies on transport processes in laser-based direct energy deposition

Additive manufacturing techniques utilizing laser as melting source involve multi-physics phenomena comprising of heat transfer, fluid flow, melting of substrate and added powder, and alloy solidification. Adequate understanding of these interlinked phenomena is essential to relate the process parameters with the properties of deposited layers. In this work, the transient process involved in laser-based melting of a SS 316 substrate while simultaneously depositing Inconel 718 powder onto a single layer has been studied. Conservation equations of mass, energy, species, and momentum are solved numerically in a 3D domain having a reference frame moving with the laser beam. An enthalpy-based technique has been used to model the phase changing phenomenon as a single-domain problem. The different melting points and vaporization beyond corresponding boiling points of elements present in IN 718 as well as in the substrate material, the momentum from pressurized shielding gas, and the penetration of laser beam into the molten pool are integrated in the model. It also incorporates free surface deformation during melting of substrate and deposition of powder. Experiments involving laser-based direct energy deposition of IN 718 powders on SS 316 substrate have been carried out for a range of laser scanning speeds and power, keeping powder deposition rate and laser spot diameter unchanged. The results obtained from the computational model have been compared with the experimental results with respect to the shape and dimensions of the dilution zone, identification of melting isotherm and corresponding estimation of melt-pool width.