Degradation, reuse and recycling of 316L powder in PBF-LB

Metal powder constitutes the most common feedstock used in metal additive manufacturing (AM), including powder bed fusion (laser beam PBF-LB, and electron beam - PBF-EB), binder jetting (BJT) and powder blown directed energy deposition (DED). Metal powder can be produced by a variety of methods, characterized by different productivity and cost, where variety of powder properties can be obtained for the same alloy system. Further on, metal powder is exposed to the processing conditions that are determined by process parameters and hardware solutions and hence differ significantly between different AM technologies. Understanding of the change in powder properties during AM processing and alloy composition and its impact on final properties of the component is required to assure successful industrial implementation of powder-based metal AM. Powder degradation in PBF-LB is strongly related to the spatter formation and its accumulation in the reused powder. Spatter formation on the other hand is strongly related to the component geometry and process parameters. However, what is important from powder degradation point of view is spatter oxidation, as it can be significantly affected by processing conditions, especially processing gas composition and oxygen potential. Hence, powder degradation is rather complex, and powder disqualification is typically determined by bulk oxygen content, that is not always representing real state of powder degradation as powder is continuously mixed with fresh virgin powder to keep bulk oxygen content below the requirements. Hence, presented work exploits possibility of powder recycling – namely, reatomization of disqualified powder and AM process waste into AM powder. Reatomization trials were performed in nitrogen and argon for 316L and enabled to obtain powder with chemical and physical properties as good or even better than virgin powder. PBF-LB processing of recycled powder showed excellent powder printability and mechanical properties showed significant improvement in comparison to the reused powder.