Recyclability of stainless steel (316 L) powder within the additive manufacturing process

Using recycled powder during the additive manufacturing processes has been a matter of debate by several research groups and industry worldwide. If not significantly different from the feedstock, the recycled powder can be reused many times without a detrimental impact on the mechanical properties of the final printed parts, which reduces the metallic powder waste and printing time. A detailed characterization and comparison of the feedstock and recycled powders is essential in order to understand the number of times a powder can be recycled. The recycled powders were sampled after 10 times reuse in the Powder Bed Fusion (PBF) process in the 3D printer. In this paper, we have performed a detailed characterization on morphology, microstructure, and the surface and bulk composition of virgin feedstock and recycled stainless steel 316 L powders (over 10 times reused), and correlated these measurements to topography, nanoindentation and hardness tests. We have also performed rarely reported synchrotron surface characterization of both powder sets in order to measure the level of oxidation of the individual metallic elements present in the virgin and recycled steel powder and the way such chemical composition changes following use in the manufacturing process. The results show more satellite and bonded particles in the recycled powder although the particle size is not broadly impacted. The atomic force microscopy results showed a smaller roughness on recycled powders measured on surfaces without satellites which might be due to less surface dendrites on recycled powder surface. Finally, a higher hardness was measured for the recycled powder resulted from the manufacturing process on grains and chemical composition. The results suggest no significant changes on the mechanical properties of the printed parts depending for a certain number of reusing cycles.