The Effect of Blue and Infrared Laser Melting Frequency on Oxide Morphology in 304L

Continuous Wave Laser Beam (LB) melting offers control over the localized heating and cooling of melt pools for welding, brazing, additive manufacturing, and solidification. Research into laser-liquid metal interactions have primarily focused on the heat and mass transport under large thermal gradients imposed by the localized melting conditions. However, little research has been conducted into varying input laser frequency and scan rate at fixed absorption to understand the effects of laser-light on surface oxide formation. This article conducts laser melting of 304L under Blue (450 nm) and Infrared (IR, 1064 nm) laser frequencies and examines their impact on laser oxide thickness, chemistry, and coloration. We find that laser frequencies induce changes in the oxide layer thickness and chemistry that cannot be explained using conventional thermal absorption shifts and fluid dynamics. We suggest that light coupling may have thermodynamic implications for the chemical potential of the liquid metal which may drive the observed phase behavior.