Characterization on the Hydrogen Embrittlement in Inconel 625 Fabricated Via Laser Directed Energy Deposition

Abstract

This study investigates hydrogen embrittlement (HE) in Inconel 625 (IN625) fabricated via Directed Energy Deposition (DED), comparing its behavior to conventionally wrought material. The microstructure of DED IN625 revealed columnar grains, high dislocation density, and elemental segregation, distinguishing it from the wrought alloy’s fine equiaxed grains. Slow strain rate tensile tests (SSRT) were conducted on specimens with and without hydrogen charging, revealing reduced ductility and evidence of hydrogen-induced quasi-cleavage fractures in both materials. Thermal Desorption Spectroscopy (TDS) demonstrated differences in hydrogen trapping behavior, with wrought IN625 showing lattice-based hydrogen trapping, while DED specimens exhibited hydrogen desorption dominated by dislocation trap sites. Fractography revealed slip bands and quasi-cleavage fracture surfaces, suggesting that the Hydrogen-Enhanced Local Plasticity (HELP) mechanism predominated in both materials, with potential Hydrogen-Enhanced Decohesion (HEDE) effects observed in inter-dendritic regions of the DED specimens. These findings highlight the critical influence of microstructural characteristics on hydrogen embrittlement mechanisms, emphasizing the need for tailored manufacturing processes to optimize hydrogen resistance in additively manufactured nickel-based superalloys.

Keywords: Inconel 625, directed energy deposition, Thermal desorption spectroscopy, Hydrogen embrittlement, Hydrogen-enhanced local plasticity