Modelling particle impact on the melt pool and wettability effects in laser directed energy deposition additive manufacturing

In powder based Laser-Directed Energy Deposition (L-DED), an incident laser melts a millimeter scale pool of metal, into which feedstock powder is sprayed. Previous high speed video reveals that powders are trapped by surface tension and float for a brief residence time before melting, directly contributing to surface roughness and loss of mass capture efficiency. In this work, influencing factors on this behavior are investigated with numerical models through coupling a three phase (gas, liquid, solid) Computational Fluid Dynamics (CFD) model with applied surface tension to a heat transfer model and observing the melting dynamics of an individual powder particle of stainless steel 316 L. Sensitivity of residence time to particle size, impact velocity, melt pool and particle temperature, surface tension, and material thermophysical properties are investigated. It is found that simulations can be condensed into a simplified analytic equation, providing a rapid, explicit estimation of residence time. The demonstrated sensitivity of L-DED to powder scale surface wettability phenomena highlights a fundamental mechanistic reason why control of feedstock powder properties is essential for reliable system behavior.