Investigation on corrosion resistance of Hastelloy N alloy after He⁺ ion irradiation

Background: The invalidation problems of irradiated Hastelloy N alloy caused by high temperature, intense irradiation and severe corrosion are the key factors to the service life of structural materials of molten salt reactor (MSR). Purpose: The aim is to investigate the effect of absorbed dose on the corrosion resistance of Hastelloy N alloy. Methods: Hastelloy N alloy was irradiated by 4.5-MeV He⁺ ions, and the absorbed doses were 0 He⁺·cm^-2, 1x10¹⁵ He⁺·cm^-2, 5×10¹⁵ He⁺·cm^-2 and 1×10¹⁶ He⁺·cm^-2 respectively. The virgin and irradiated specimens were immersed into molten fluoride salts at 700℃ for 300 h. Then the corroded specimens were imaged by scanning electron microscopy and analyzed by synchrotron radiation microbeam X-ray fluorescence (μ-XRF). Results: The weight-loss results showed that the corrosion generally correlated with the absorbed dose of the alloy. The μ-XRF results indicated that the corrosion was mainly due to the dealloying of alloying element Cr in the matrix. Conclusion: The density of dislocations of Hastelloy N alloy increased with the absorbed dose, which acted as quick paths for Cr element diffusion, and the diffusion of element Cr out of matrix became easier. Finally became weak of the corrosion resistance of Hastelloy N alloy. (authors)