  This study demonstrates the significant effect of the recoil pressure and
Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless
steel. A three-dimensional high fidelity powder-scale model reveals how the
strong dynamical melt flow generates pore defects, material spattering
(sparking), and denudation zones. The melt track is divided into three
sections: a topological depression, a transition and a tail region, each being
the location of specific physical effects. The inclusion of laser ray-tracing
energy deposition in the powder-scale model improves over traditional
volumetric energy deposition. It enables partial particle melting, which
impacts pore defects in the denudation zone. Different pore formation
mechanisms are observed at the edge of a scan track, at the melt pool bottom
(during collapse of the pool depression), and at the end of the melt track
(during laser power ramp down). Remedies to these undesirable pores are
discussed. The results are validated against the experiments and the
sensitivity to laser absorptivity is discussed.
