Hot corrosion of additively manufactured Inconel 718 in molten solar salt: Effects of heat treatment and long-term exposure

Additive manufacturing offers unprecedented opportunities to tailor alloy microstructures; however, the long-term corrosion behaviour of additively manufactured Ni-based superalloys in molten salt environments remains insufficiently understood. In this study, the hot corrosion behaviour of PBF-LB-produced Inconel 718 was investigated in molten Solar Salt with emphasis on the role of post-processing heat treatments and prolonged exposure. Specimens in the as-built, solution-annealed, and double-aged conditions were exposed for up to 900 h and characterized using mass loss measurements, X-ray diffraction, electron backscatter diffraction, transmission electron microscopy, and cross-sectional SEM–EDS analysis. The as-built condition exhibited predominantly surface-limited oxidation with extremely thin oxide layers and negligible inward corrosion penetration, which is attributed to the retained cellular substructure and associated microsegregation that disrupt continuous diffusion pathways for aggressive species. In contrast, solution annealing activated grain-boundary-assisted degradation, resulting in thick but chemically unstable oxide scales and significant inward corrosion propagation with increasing exposure time. Localized Cr-depleted, Ti/Al–O-enriched reaction zones and near-surface void formation further indicate the breakdown of protective oxide behaviour in the solution-annealed state. Double aging moderated the corrosion response through γ' and γ″ precipitation, as confirmed by TEM analysis, which stabilizes the microstructure and limits the development of continuous grain-boundary corrosion pathways. Quantitative analysis shows that oxide thickness alone is not a reliable indicator of corrosion resistance. Although the phase assemblage of corrosion products becomes increasingly similar with prolonged exposure, post-processing treatments strongly influence time-dependent corrosion response, morphology, and spatial distribution of degradation.