Long-term corrosion behavior of Al-based coatings in flowing Pb–15.7Li, produced by electrochemical ECX process

Abstract

RAFM-steels such as Eurofer are considered as structural materials for breeding blankets in future fusion power plants (DEMO). Some of these blankets e.g. HCLL, WCLL and DCLL, use flowing Pb–15.7Li as liquid breeding material. In these concepts, the breeding material will be in direct contact to the structural material at operational temperatures of up to 550 °C. However, bare RAFM steels suffer from strong corrosion attack with corrosion rates between 100 and 400 µm under these conditions. To protect bare RAFM steels from corrosion, Al-based coatings are considered as corrosion barriers. Different coating processes were developed in the past, with focus on electrochemical processes within the last decade. The currently most promising one is the so-called ECX process. Based on the electrodeposition of aluminum from an ionic liquid, it produces smooth and uniform Al enriched scales. These ECX coatings have already shown good short- to mid-term corrosion resistance in flowing Pb–15.7Li for up to 4000 h.In the current study, the long-term corrosion behavior of aluminum-based coatings on Eurofer made by ECX process was investigated. Exposure times of up to 10,000 h in flowing Pb–15.7Li were reached under fusion relevant conditions, i.e. 550 °C and a flow velocity of 0.1 m/s. In comparison to bare Eurofer the corrosion attack is drastically reduced while corrosion rates lay below 20 µm/a. Additionally, it was found that the corrosion behavior is also superior to the corrosion behavior of Al-based barriers produced by the ECA process after long-term exposure in Pb–15.7Li.