Gaseous hydrogen embrittlement of 3D-printed Inconel 718 manufactured from sustainable feedstock
N.K. Mohandas (TU Delft - Mechanical Engineering)
Popovich Vera – Mentor (TU Delft - Team Vera Popovich)
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Abstract
Laser powder bed fusion (L-PBF) is an additive manufacturing (AM) technology that has been gaining a lot of interest as it allows to produce parts with complex geometries and eliminate expensive tooling. Unlike the conventional manufacturing processes where material is removed to make the final component; AM part is manufactured layer-wise as per the required geometry. Due to this, the material wastage in the AM process is minimal. In addition, powder feedstock produced from recycled materials can promote a more sustainable L-PBF. It is however known that properties of L-PBF material are influenced by numerous variables, among which is the powder feedstock. It is thus important to investigate mechanical and other functional properties of AM components produced from recycled feedstock.
Inconel 718 is a Nickel-based superalloy that is often used in turbine blades and heat exchangers where high performance in extreme environments is required. Good mechanical properties of Inconel 718 and high design flexibility enabled by L-PBF process allow to expend applications of this alloy to fuel injection nozzles used for liquid hydrogen fuel engines or tubing for fuel transport in the engine. Although Inconel 718 shows good performance in high temperature applications, in the presence of hydrogen the material is found to lose ductility.
This study investigated the in-situ gaseous (under 150 Bar) hydrogen embrittlement behaviour of L-PBF Inconel 718 manufactured from sustainable feedstock. It was found that despite its higher yield strength, heat treated L-PBF samples demonstrate 64% lower degree of hydrogen embrittlement compared to the wrought counterpart. This was linked to anisotropic microstructure induced by L-PBF process, which was found to cause directional embrittlement unlike the wrought samples showing isotropic embrittlement.
In conclusion, this study shows that L-PBF Inconel 718 produced from recycled feedstock shows better hydrogen embrittlement resistance compared to the wrought sample. Furthermore, the unique anisotropic properties, seen in this study for L-PBF Inconel, could be considered further in component design to help minimise the degree of hydrogen embrittlement.