Corrosion of Incoloy 800H alloys with nickel cladding in FLiNaK salts at 850 °C

Highlights: • The influence of Fe and Ni ion on molten FLiNaK salts corrosion was investigated. • Cr- depletion layer and Fe-rich layer form in the alloy surface. • The chemistry criterion of a good cladding is Fe + Cr ≤ 11 wt.%. • Cr element is found to be hardly depleted from Σ3 type grain boundaries. - Abstract: The corrosion of 800H alloy with and without Ni-cladding, as well as GH3535 alloy, in molten FLiNaK salts at 850 °C has been investigated. Results show that Cr and Fe are depleted from the alloys surface and grain boundaries, where "diffusion paths" are formed. The corrosion process is mainly controlled by the redox reaction of impurity metal ions with Fe and Cr at the alloy surface, and an alloy or cladding layer chemistry criterion is suggested as Fe + Cr ≤ 11 wt.%. Cr element is found to be hardly depleted from Σ3 type grain boundaries.