Influence of Heat Treatment on the Hydrogen Embrittlement of Inconel 718 Fabricated by Laser Powder Bed Fusion

The influence of post-fabrication heat treatment on the hydrogen-assisted failure in Inconel 718 fabricated by laser powder-bed-fusion was investigated through a series of tensile experiments. Samples subjected to two different heat treatments, viz. direct aging (DA) and homogenization plus aging (HA), were examined. Detailed microstructural analysis revealed that the DA sample exhibited a solidification substructure decorated with a high density of dislocations and precipitates while such a substructure was absent in the HA sample. The DA sample exhibited a comparatively higher strength, but a lower resistance to hydrogen embrittlement. Through a statistical analysis of the hydrogen-assisted cracks, it was revealed that the severe hydrogen embrittlement of the DA sample was attributed to the significant hydrogen-assisted intergranular cracks that occurred without the aid of slip localization. These results are discussed in terms of the changes in microstructure upon heat treatments, and their influences on the hydrogen trapping sites.