Assessing metal powder quality for additive manufacturing using diffuse light spectroscopy

The ability to maintain repeatable quality of metal powder is fundamental to a robust metal additive manufacturing (AM) process. The main powder degradation mechanisms in powder-based AM are the shift in the powder size distribution (PSD) and an oxygen pickup. In this study, we purposely oxidized and fractionated titanium-based and nickel-based alloy powders to evaluate the usefulness of diffuse light spectroscopy in detecting powder condition changes. For the experiment, six gas-atomized powders were used: Titanium grade 2, Ti-5Al-5Mo-5V-1Cr-1Fe, Ti-6Al-4V, Inconel 718, Inconel 625 and CM 247-LC. All powders were tested in terms of their morphology, chemical composition, and diffuse light reflectance. A strong linear correlation of the same character was observed between both PSD and reflectance, and between oxidation level and reflectance. With increasing particle sizes and oxygen levels, a decrease of reflectance is observed. We conclude that diffuse light spectroscopy is a promising measurement method for AM metal powders.