Characterization of recycled Inconel 718 metal powder for assessing its reusability in the laser powder bed fusion process

Additive manufacturing technologies such as laser powder bed fusion (LPBF) provide unprecedented abilities to manufacture complex 3-D parts and structures; however, the process produces leftover metal powder that is often unused, resulting in significant cost and disposal overhead. Towards this end, to ensure the ability to recycle the unused powder that is typically found within the build volume and in the overflow compartments of LPBF systems, a thorough chemical and structural analysis is required. Such an analysis will help in determining the extent of recyclability and reusability of the unused powder. For these purposes, characterization of recycled powder for Inconel 718 was performed in this work as a function of build-cycle to compare and contrast the evolution in physical and chemical properties such as particle size distribution, morphology, and composition. We note that the analysis was carried out for 21 build-cycles. Characterization of the particle size distribution and circularity was performed using traditional scanning electron microscopy methods and that information was later compared to measurements of surface profile using coherent scanning interferometry. Reusability was assessed using these results in conjunction with chemical analysis of the powder that was carried out using energy dispersive X-ray spectroscopy. For the extent of build-cycles considered in this work, it was seen that the physical and chemical changes in the recycled powder were will within accepted limits for powder usage and that with appropriate measures, recycled powder can be re-incorporated for subsequent builds without compromise in the powder quality. This study provides a pathway for greatly reducing powder consumption and thus cost during the LPBF process.