Exploring the efficiency of powder reusing as a sustainable approach for powder bed additive manufacturing of 316L stainless steel

The efficiency and sustainability of Laser Powder Bed Fusion (L-PBF) greatly depends on the ability to recycle the used powder since a large portion of the feedstock remains unsolidified surrounding the printed part. To assess the impact of reusing iterations on the properties of the feedstock and printed part, we employed thermodynamic simulation to study oxidation in the building chamber. We then compared the 5 times reused powder of austenitic steel 316L (SS316L) and the printed part with its virgin counterpart. Our findings revealed that minor residual oxygen in the building atmosphere reacts with the molten pool and hot spatters, leading to the formation of Rhodonite (MnSiO3) inclusions. As sieving cannot remove oxides smaller than steel particles, the repetition of feeding the used powder into the printing process directly increases the fraction of oxides in the printed parts. The increase in inoculated oxygen by reusing, coupled with the dissolution of oxides into the molten pool, facilitates the formation of Spinel (MnCr2O4) and Tridymite (SiO2) oxides, as well as clustered inclusions. While small oxides anchor cellular structures, stress concentration on the coarse fragile inclusions leads to sudden rupture and weaker tensile strength of the printed part with reused SS316L powder.