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Description
In Laser Powder Bed Fusion (LPBF), a significant amount of metallic powder is not melted by the laser beam. Costs and material yield strongly depend on the ability to reuse metal powder efficiently. However, some of the unfused powder is exposed to high temperatures during the manufacturing process in an imperfectly controlled atmosphere. Therefore, there is a need to study and understand powder degradation during the process and its direct effects on the printed parts. One batch of gas-atomized 316L stainless steel powder was used, recovered, sieved and reused to produce 12 successive LPBF prints without adding any virgin powder. Both recycled powders and elaborated parts were characterized throughout each iteration. Particles analysis was carried out using laser granulometry, scanning electron microscopy, flowmeter funnels, inert gas fusion, and X-ray diffraction. Solidified specimens features were investigated by means of optical microscopy, scanning electron microscopy, electron backscattered diffraction, microhardness and uniaxial tensile testing. Powders morphology, rheology, microstructure and oxygen content display slight changes with recycling, along with parts density and mechanical properties. The effects of processing conditions, especially the chamber oxygen content were also studied, and strongly influence the kinetics of degradation.