Nonthermal Hydrogen Plasma Process for the Reuse of Metal Additive Manufacturing Feedstock Powder

Abstract

Metal powder-based additive manufacturing (AM) processes face a significant challenge with an increasing oxygen concentration (predominantly as surface oxides) in metal powders during reuse cycles. This increased surface oxidation, occurring at the high temperatures encountered by powders during the printing process, ultimately surpasses industry-acceptable quality limits. Powder bed fusion (PBF) AM processes deposit metal powders layer by layer, resulting in wasted feedstock, which can increase unit costs and have adverse environmental impacts. It is therefore essential to develop and optimize processes to enable the recycling and reuse of metal feedstock powders to establish sustainable AM processes industry wide. To address this challenge, we report the application of a novel low-temperature nonequilibrium hydrogen (H₂) plasma- (HP-) based deoxidation process for efficient recycling and reuse of metal powder in AM processes. The technique involves the highly reactive species generated in a H₂-fed low-pressure radio frequency (RF) plasma discharge dynamically interacting with oxidized powder in a quartz tube reactor, thereby reducing oxide content without adversely affecting particle size or morphology. In this study using a bronze copper–tin alloy (CuSn10) powder, a >60% reduction in oxide content was achieved through the HP treatment of oxidized CuSn10 powder samples at the 10 g/batch scale as measured via inert gas fusion (IGF), which is a significant improvement and well below the measured oxygen content of the as-received virgin CuSn10 powder. HP-treated powder was further characterized to determine treatment effect on powder morphology, bulk particle structure, and surface chemical composition via laser diffraction and dynamic imaging analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. Initial demonstration of process scale-up showed a >50% reduction in oxide content at an increased batch size of 100 g/batch.