Abstract: The effects of the Laves-decorated dendrite structure on the hydrogen-assisted cracking behavior of the SLM-718 alloy were investigated. The Laves phase exhibits a hydrogen desorption activation energy of 47.67 ± 7.85 kJ mol^-1. The results of in situ scanning Kelvin probe force microscopy and hydrogen microprint technique provide direct evidence of the hydrogen trapping by the Laves phase. The high-density dendrite walls consisting of entangled dislocations exhibit an inhibitory effect on hydrogen diffusion. Atomic-scale characterization reveals that dislocation stacking at the Laves/γ-matrix interface induces the formation of dislocation defects and a high-stress concentration in the Laves phase. The presence of hydrogen further promotes the formation of micropore defects and the embrittlement of the Laves phase. Hydrogen-promoted dislocation slip localization and hydrogen-induced reduction of interatomic bonding are the primary reasons for the Laves phase fracture and debonding at the Laves/γ-matrix interface. The coalescence of micropore defects ultimately leads to hydrogen-induced crack formation.

Key words: Selective laser melting, Nickel-based alloy, Hydrogen embrittlement, Laves phase, Dendrite structure