Effects of gas composition and pressure level on powder spattering and denudation in laser powder bed fusion

Powder spattering and denudation in laser powder bed fusion (LPBF) processes lead to defects in the final part, and these powder behaviors are significantly affected by the chemical composition and pressure level of the ambient gas. In this work, a three-dimensional multi-physics model for LPBF was developed to simulate the process dynamics and its effects on the powder behavior, and it was combined with in-situ imaging experiments to study the LPBF cases of different ambient gases (Argon vs. Helium) and pressure levels (1-bar vs. 5-bar). The evaporation kinetics, vapor plume behavior, and powder behavior as functions of the gas composition and pressure level were quantitatively analyzed based on the simulation results. Three different types (fusion, spattering, and denudation) of particle trajectories were identified, and their spatial distribution and driving mechanisms were discussed. The simulation showed reduced powder denudation and spattering in Argon (vs. Helium) or with 5-bar pressure (vs. 1-bar), which was consistent with the experimental observations. The Argon gas slowed down the entrainment flow with its higher density, and the 5-bar pressure suppressed the entrainment flow as it reduced the metal evaporation. The weaker entrainment flow drove fewer particles to move toward the laser (i.e., reduced entrainment) and thus fewer particles can interact with and be accelerated by the vapor plume (i.e., reduced spattering).