Corrosion Behavior of Ni-Based Superalloys in LiCl-KCl Molten Salt
Molten salt electrorefining is the core process unit of spent nuclear fuel dry post-processing,and its reaction vessel needs to be used for a long time in a high-temperature,LiCl-KCl molten salt environment.The selective dissolution of the active alloying element Cr makes it difficult to form a passivation Cr2O3 protective film,and the structural material faces serious corrosion problems,which seriously hinders the engineering application of dry post-treatment technology.so the structural materials face serious corrosion problems.Ni-based superalloys have stable thermodynamic properties in high-temperature chloride molten salts and are potential candidate materials for electrolytic refining reaction vessels.Ni-based superalloys are potential candidates for electrorefining reaction vessels.But the effect of key alloying elements such as Mo and W on the corrosion resistance of Ni-based superalloys in LiCl-KCl molten salt is not clear.The corrosion behavior of five Ni-based superalloys,Haynes 230,Inconel 625,GH 3535,Inconel 690 and GH 4169,in LiCl-KCl molten salt at 550℃under argon atmosphere was studied by immersion corrosion.The composition and morphology of the corrosion products were analyzed by X-ray diffraction,scanning electron microscopy and energy spectrum analysis.The results show that the corrosion loss of the five Ni-based superalloys is Inconel 625>GH 3535>Haynes 230>Inconel 690>GH 4169.Inconel 625 and GH 4169 alloys have a Mo-rich oxide film on the near surface of the matrix,resulting in poor thermal compatibility between the outer(Cr,Fe)2O3 and the matrix.Compared with Inconel 690 alloy,GH 3535 alloy with low Cr content inhibits the selective dissolution of Cr element,but also reduces the oxidation resistance.Haynes 230 alloy has the best corrosion resistance among the five Ni-based superalloys with W-rich oxides formed on the outer surface,which effectively blocks the erosion of Cl-.
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