FLUORIDE CORROSION OF TI-GRADE 7: EFFECTS OF OTHER IONS

摘要

The effects of chloride, sulfate, and nitrate on the fluoride ion local attack of Ti-Grade 7 (Ti-7: UNS R52400) were investigated. It was observed that the most severe local attack on Ti-7 occurred at approximately 120 deg C, and at neutral pH. A large chloride: fluoride ratio (10: 1 by mole) was necessary to produce visible severe attack in immersion tests, but electrochemical studies detected a narrowing of the passive region at chloride: fluoride ratios as small as 1.1: 1 by mole. The addition of large amounts of sulfate slowed, but did not inhibit pitting and stress corrosion cracking of Ti-7 U-bends, but the addition of nitrate is suspected to act as an effective inhibitor. Polishing of the titanium surface to micron scale also decreased the likelihood of the initiation of local attack.