Oxidation behaviour of PM-C26M FeCrAl alloy in low-temperature steam 400 – 900 °C

Abstract

Iron-chromium-aluminum (FeCrAl) alloys are the primary candidate for serving as an accident tolerant fuel cladding, replacing zirconium (Zr)-based cladding. This preference stems from the high corrosion resistance under both operating and accident conditions in light water reactors (LWRs). To successfully implement this alloy as a cladding material in LWRs, the corrosion behavior under various conditions needs to be understood. While recent studies have focused on high-temperature steam conditions (>1000 °C) and operating conditions (∼300 °C), there is a notable gap in research exploring the steam temperature range above 300 °C and below 1000 °C. This study specifically investigated the formation of oxide layers on powder metallurgy (PM)-C26M FeCrAl in steam at temperatures ranging from 400 °C – 900 °C. It was found that within the temperature range of 400 °C – 600 °C, a duplex oxide layer emerges, with Fe-oxide in the outer layer and Cr/Al-oxide in the inner layer. At 500 °C, the outer layer consists of α-Fe₂O₃ crystals with Cr/Al-oxides in the inner layer. The initial occurrence of a single oxide layer mostly comprised of alumina (Al₂O₃) is observed at 700 °C, remaining consistent from the 700 °C – 900 °C range. The Al₂O₃ layer is nanocrystalline, but not as thick or as uniform in composition as that observed in high-temperature steam environments. Notably, the Al₂O₃ layer has Fe, Cr, and molybdenum (Mo) precipitates dispersed throughout. Increasing the temperature decreases the presence of these precipitates in the oxide layer, and an increase in either temperature or time results in an increase in the thickness of Al₂O₃ layer.