A comprehensive analytical-computational model of laser directed energy deposition to predict deposition geometry and integrity for sustainable repair

Abstract

Laser directed energy deposition (DED) is an innovative additive manufacturing technology with tremendous potential for remanufacturing and repairing critical components. For sustainable repair, it is necessary to control the deposition geometry and integrity in terms of residual stresses and dilution. Obtuse contact angles and inadequate dilution can lead to inter-track porosity and cracks at the edge of the deposition-substrate interface. In addition, the fatigue life of the restored part is compromised if tensile residual stresses are induced in the deposited layer. A comprehensive modeling approach presented in this paper integrates analytical formulations for the laser-powder interaction and the powder entrapment in the melt pool, with the finite element models for determining the melt pool characteristics and the residual stresses. This model captures the physics of the key phenomena in DED, namely, power attenuation due to laser-particle interaction, melt-pool formation, powder catchment in the melt pool, and the residual stress evolution due to differential thermal contraction and metallurgical transformations. The model predictions have been experimentally validated for residual stresses, dilutions, catchment efficiencies, powder flux, and deposition geometries for crucible particle metallurgy (CPM 9V) steel powder on H13 tool steel. CPM 9V is a preferred material for repairing H-13 molds. Extensive simulations have been carried out using the comprehensive analytical-computational model to develop data-driven expressions for deposition geometry, normalized dilution, and residual stress as a function of process parameters (laser power, scan speed, and powder feed rate). For identifying the preferred deposition regime, these relations are employed to bifurcate the entire operating space into obtuse and acute contact angle, insufficient and sufficient dilution, tensile and compressive residual stress. Higher Pv/m˙ values yield depositions with the desired acute contact angles and higher specific energies (P/vd) induce favorable compressive longitudinal residual stress in the depositions.