The role of oxides in hydrogen trapping and hydrogen-assisted crack propagation in direct energy deposition nickel alloy 625

This study investigates the hydrogen-induced stress cracking (HISC) behaviour of additively manufactured Nickel Alloy 625 (NA625) produced by Laser-Based Direct Energy Deposition (DED-LB625), with particular emphasis on the role of oxide features within the microstructure. DED-LB625 exhibited reduced sensitivity to hydrogen exposure compared with wrought NA625 (W625), demonstrated by a smaller reduction in ultimate tensile strength and improved ductility under hydrogen-charging conditions. Hydrogen desorption measurements revealed a lower mobile hydrogen content in the additively manufactured material, which is indicated in ToF-SIMS and TDS analysis, with this effect attributed to hydrogen trapping at (Nb,Si) rich oxides. Crack propagation was found to preferentially follow subgrain cellular structures enriched with Laves phase, as demonstrated by TEM, whereas cracks interacting with oxide features showed evidence of blunting and local arrest. These findings highlight the potential for DED-based additive manufacturing to enhance hydrogen tolerance in NA625, supporting its application in hydrogen-containing Oil & Gas environments.