EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Additive manufacturing is used to build complex parts that are difficult to produce by conventional methods. Selective laser melting process is used to melt metallic powders layer-by-layer and form near net-shape parts. However, during the process, a large amount of powder remains unmelted. The powder is generally reused but its quality may decrease after tens of building cycles, which may have an impact on manufactured parts.
The aim of this study is to assess the effect of Inconel 718 powder recycling, by the use of multi-scale analysis of the microstructure. Samples are manufactured from virgin and reused (after 50 building cycles) powders and analyzed in their as build state and after heat treatment. Grain morphology, crystallographic texture, precipitation is discussed and compared between virgin and recycled powder made samples. Their mechanical behavior is also characterized by monotonous tensile tests and fatigue tests.
No significant changes are observed in the microstructure, both as-build and heat-treated, after 50 construction cycles. The as-build state samples are characterized by the same dendrite size and grain size, while the oxygen content is slightly higher for the reused powder samples. High cycle fatigue tests show a slight reduction in fatigue life. However, the influence of recycling is insignificant compared to the variation in process parameters observed on other studies. After solution heat treatment, followed by ageing, recrystallization and precipitation are examined. Observations are currently in progress. At this time however, no clear differences in grain morphology or precipitate density are evaluated, which is consistent with the similarity of the as-built samples. This should lead to a great similarity in their mechanical properties. In conclusion, this work shows that process parameters are more critical than the reuse of Inconel 718 powder on mechanical properties.