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Hydrogen embrittlement evaluation of wire arc additive manufactured 316 L stainless steel: Evidence of hydrogen induced hardening, enhanced decohesion, and assisted localized deformation
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DOI：10.1016/j.addma.2026.105237.png)
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Abstract
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Hydrogen embrittlement poses a significant challenge for the safe deployment of hydrogen technologies, especially in additive manufactured materials intended for storage and transport infrastructure. This study investigates the interaction between hydrogen and the dual-phase microstructure of wire arc additive manufactured 316 L stainless steel. The as-built material consists of δ-ferrite phase embedded within a γ-austenite matrix, with pronounced strain incompatibility across γ/δ interfaces. Electrochemical hydrogen charging combined with melt extraction and thermal desorption spectroscopy are employed to quantify hydrogen uptake and diffusion behavior, while tensile, nanoindentation, and load–unload–reload (LUR) tests are used to evaluate mechanical response. Tensile testing results reveal that hydrogen increases yield strength and work-hardening rates while significantly reducing ductility, which indicates concurrent hardening and embrittlement. LUR tests reveal that back-stress is the dominant strengthening mechanism, which is further amplified by hydrogen enhanced slip planarity and dislocation pile-ups at γ/δ interfaces. Nanoindentation shows a more pronounced hardening effect in the γ-austenite phase compared to the δ-ferrite phase, attributed to higher hydrogen solubility in the FCC lattice. Fractography confirms a transition from ductile microvoid coalescence to mixed brittle–ductile fracture, governed by hydrogen concentration gradients across the specimen thickness. Electron backscatter diffraction and electron channeling contrast imaging demonstrate that hydrogen-assisted cracks preferentially initiate both along the γ/δ interfaces and within the δ-ferrite phase via hydrogen-enhanced decohesion. Crack propagation, however, occurs through the γ-austenite matrix via hydrogen-enhanced localized plasticity and shear localization. These findings provide a mechanism-based understanding of how microstructural heterogeneity in WAAM 316 L components governs their susceptibility to hydrogen degradation.
Keywords:
Hydrogen embrittlement
Wire arc additive manufacturing
316 L stainless steel
Microstructural heterogeneity
Hydrogen-induced hardening
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