Tailoring dendritic structure to improve hydrogen embrittlement resistance in selective laser-melted inconel 718

The unique dendritic structure produced by selective laser melting of Inconel 718 offers distinct advantages in controlling the alloy's resistance to hydrogen embrittlement (HE). This study tailored dendritic structures to enhance the HE resistance of Inconel 718 and analyzed the differences in HE resistance among various dendritic structures. Increasing laser power from 250 W to 430 W deepened melt pools, reducing the width-to-depth ratio from 2.09 to 1.43. This lowered the heat dissipation, thereby decreasing the cooling rate. The increased melt pool depth favored epitaxial growth of columnar dendrites along the build direction, while the extended solidification time facilitated competitive growth and coarsening. This ultimately increased columnar dendrite spacing by 24%, cellular dendrite size by 38%, and columnar proportion by about 20%. Concurrently, the intensified Marangoni convection at higher laser power enhanced mass transfer and Nb homogenization, reducing the volume fractions of long-chain and granular Laves phase by 4.1% and 8.4%, respectively, while the HE sensitivity decreased by 27.1%. The hydrogen microprint technique revealed that hydrogen was preferentially trapped in Laves phases at dendrite walls. During deformation, dislocations accumulated around Laves phases, inducing stacking faults that fractured in the presence of hydrogen, generating microvoids. Long-chain Laves phases exhibited more severe strain concentration than granular Laves phases, facilitating crack initiation. The enhanced HE resistance originated from competing effects: although cracks propagated preferentially along columnar dendrite boundaries, the enlarged dendrite spacing reduced the areal density of Laves phase particles, which disrupted the continuity of hydrogen-assisted crack paths.