Corrosion mechanisms of nickel-based alloys in chloride-containing hydrofluoric acid solution

In this study, the corrosion mechanisms of three nickel -based alloys in chloride-containing hydrofluoric acid solution are studied to elucidate the effects of Cu, Cr and Mo on the surface chemistry behavior. Results show that the addition of chloride ion accelerates corrosion of Monel 400 and Inconel 600, while inhibits corrosion of Hastelloy C-276. Such a discrepancy in corrosion resistances of three nickel-based alloys is ascribed to the competitive adsorption between fluoride and chloride ions as well as their interaction with passivation. Particularly, the preferentially adsorbed chloride ion hinders the oxidation of Cu and Cr, and the oxide-dominant passive film turns into fluoride-dominant corrosion product film that accelerates corrosion of Monel 400 and Inconel 600. While for Hastelloy C-276, Mo enriches as stable MoO2 in the passive film, which prevents the incorporation of chloride and fluoride ions into the passive film, leading to increased corrosion resistance in chloride-containing HF solution.