Self-healing behaviors of protective oxide films in liquid metal

Kawarai, Atsushi*; Obayashi, Hironari  ; Saito, Shigeru   ; Sasa, Toshinobu   ; Kondo, Masatoshi*

FeCrAl alloys are promising structural materials for liquid metal blankets of fusion reactor because they form a self-healing alumina film on the surface and exhibit excellent coexistence with liquid metal. The purpose of this study is to clarify the formation and repair behavior of the oxide film in liquid metal. The corrosion tests were performed using the high temperature lead-bismuth flow corrosion test loop (OLLOCHI) for accelerator-driven system research at JAEA. Test conditions were lead-bismuth temperature of 450/350C and oxygen concentration of 10wt%. The specimens were strips of APMT with and without pre-oxidation. Pre-oxidation treatment formed an alumina film of about 400 nm on the surface of the specimens, and no corrosion was observed after 2,000 hours of corrosion testing. On the other hand, the specimen without pre-oxidation formed an alumina film of about 37 nm on the surface after corrosion testing, and no corrosion was observed. To further evaluate the self-healing behavior of the oxide film, the specimens were artificially damaged by grinding to a width of 2 mm and subjected to 2,000-hour corrosion test. As a result, it was found that an oxide film of about 30 nm thickness was re-formed in the damaged area of the specimen. This is almost the same thickness as the undamaged area, and no corrosion was observed. It was found that APMT steel, with or without pre-oxidation, exhibited excellent coexistence in liquid LBE by self-forming and repairing a highly corrosion-resistant film.