This study presents a novel in situ laser-induced breakdown spectroscopy system for monitoring metal vapors produced by the intense laser-metal interactions in laser powder bed fusion additive manufacturing and laser welding. The insights from this new technique reveal changes in alloy compositions and provide the first in situ validation of multi-physics vaporization simulations, alongside synchrotron X-ray radiography experiments.
Abstract
Understanding vaporization phenomena in laser powder bed fusion (LPBF) additive manufacturing has proven challenging; the links between laser-induced metal vaporization, rate of elemental loss, and composition irregularities remain unclear. Here, the vapor plume composition and preferential vaporization effect is quantified during LPBF, using in situ 1 kHz laser-induced breakdown spectroscopy with correlative X-ray synchrotron radiography, multi-physics simulations, and energy dispersive X-ray spectroscopy. It is demonstrated that vaporization increases under keyhole mode, and preferential vaporization causes elemental loss rates of Ni ≈ Fe > Cr > Mo in a Ni-based superalloy, IN625. It is found that the melt pool temperature (T ≈2300 K) can be approximated by cross-referencing vapor pressures, and Raoult’s law inadequately describes preferential vaporization. Three simulation approaches are compared to show that introducing temperature-dependent thermophysical properties improves model predictions. The insights into the vapor dynamics of laser-processed IN625 enhance the understanding of compositional changes and elucidate methods to optimize simulations.
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