Effetti dell’assorbimento di idrogeno gassoso sul comportamento meccanico dell’Inconel 718 prodotto mediante Selective Laser Melting

Inconel 718 is widely used for components subjected to aggressive environments, often in presence of elevated temperatures, which can promote the absorption of hydrogen into the metal. The current energetic policies consider hydrogen a clean fuel, an energy carrier, and a storage solution, introducing new challenges in terms of storage, transport, and usage in elevated temperature environments. However, it is well-known that hydrogen absorption significantly affects the material's mechanical properties. Inconel 718 is increasingly employed to produce structural components through the Selective Laser Melting (SLM) technology, allowing the manufacturing of functionally optimized shapes and overcoming the traditional manufacturing limitations. However, the SLM process introduces a peculiar microstructure and severe residual stresses that can affect hydrogen migration and accumulation. While the mechanical properties were deeply investigated in recent years, the resistance of SLMed Inconel 718 to the Hydrogen Embrittlement (HE) produced by gaseous hydrogen is still an open issue. The present work deals with the assessment of the hydrogen susceptibility of the SLMed In718 in presence of gaseous hydrogen. The material was tested in the as-built and aged conditions. Hydrogen was introduced into the material by exposing a set of specimens to a hydrogen-rich environment at elevated temperatures, enhancing its diffusivity in the material and simulating possible operating conditions of In718 components. Slow strain rate tensile tests were carried out on plain specimens. The final hydrogen concentration was measured by Hot Extraction Method (HEM) for each specimen at the end of the test. Fractographic analysis was then carried out, to identify the damage nucleation and evolution as a function of the hydrogen intake, as well as the hydrogen penetration into the material. A correlation among the main material mechanical properties, in particular elongation at fracture, and the hydrogen content was finally derived.