Influence of powder recycling protocol on powder, microstructure and mechanical properties of Inconel 718 manufactured by laser powder bed fusion

To reduce the manufacturing costs as well as the environment footprint of laser powder bed fusion additive manufacturing, powder is generally recycled from a production to the next one which may affect the manufacturing and further properties of the final part. This study investigates the influence of powder recycling on Inconel 718 fabricated by Laser Powder Bed Fusion (LPBF), comparing two industrial protocols: with and without addition of virgin powder, over up to 54 recycling cycles. Powder characteristics (composition, size, circularity, flowability), sample microstructures (including porosity), and mechanical properties (tensile and fatigue) were evaluated with or without precipitation heat treatment. A slight increase in oxygen content and a reduction in particle circularity were observed with recycling, more pronounced for the accelerated protocol without virgin powder addition. However, all powders remained within industrial specifications. Powder flowability improved with recycling, and porosity evolution was found to depend on the protocol: fewer critical-sized pores were found with the refreshment approach with virgin powder addition. Mechanical properties in tension remained unaffected, while fatigue life showed no significant degradation across protocols and conditions. These results demonstrate that, when properly managed, powder recycling regardless of powder addition has limited impact on IN718 part quality in LPBF, supporting its implementation for cost and sustainability reasons.