In situ X-ray imaging of defect and molten pool dynamics in laser additive manufacturing

TLDR

Laser–matter interaction and solidification phenomena in laser additive manufacturing remain unclear, hindering process development and optimisation. The study employs in situ, high‑speed synchrotron X‑ray imaging to reveal the physical phenomena occurring during deposition of the first and second layer melt tracks. A mechanism map is developed that predicts melt feature evolution, showing that decreasing linear energy density transforms continuous hemi‑cylindrical tracks into disconnected beads, while increasing laser power improves molten pool wetting. Results demonstrate that a laser‑induced gas/vapour jet spats melt tracks and denuded zones at ~1 m s⁻¹, Marangoni‑driven flow migrates pores at ~0.4 m s⁻¹, and laser re‑melting dissolves and disperses pores, clarifying key physics essential for LAM development.

Abstract

Abstract The laser–matter interaction and solidification phenomena associated with laser additive manufacturing (LAM) remain unclear, slowing its process development and optimisation. Here, through in situ and operando high-speed synchrotron X-ray imaging, we reveal the underlying physical phenomena during the deposition of the first and second layer melt tracks. We show that the laser-induced gas/vapour jet promotes the formation of melt tracks and denuded zones via spattering (at a velocity of 1 m s −1 ). We also uncover mechanisms of pore migration by Marangoni-driven flow (recirculating at a velocity of 0.4 m s −1 ), pore dissolution and dispersion by laser re-melting. We develop a mechanism map for predicting the evolution of melt features, changes in melt track morphology from a continuous hemi-cylindrical track to disconnected beads with decreasing linear energy density and improved molten pool wetting with increasing laser power. Our results clarify aspects of the physics behind LAM, which are critical for its development.