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

• The PM-C26M FeCrAl alloy was exposed to steam at temperatures ranging from 400 °C to 900 °C in isothermal tests. • The oxide layers that form from 400 °C to 600 °C follow a duplex layer structure with an outer layer of Fe-oxide that takes the form of α-Fe 2 O 3 starting at 500 °C and an inner layer of Cr/Al-oxide. • A single layer of Al 2 O 3 forms on the surface of the alloy starting at 700 °C and gets thicker at higher temperatures. • The weight change of the 400 °C steam exposed sample was greater than the 500 °C to 700 °C steam exposed samples, indicating that dissolution and spallation of the metal and oxides are drastically lower at 400 °C than higher temperatures. 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 to 900 °C. It was found that within the temperature range of 400 °C to 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-Fe 2 O 3 crystals with Cr/Al-oxides in the inner layer. The initial occurrence of a single oxide layer mostly comprised of alumina (Al 2 O 3 ) is observed at 700 °C, remaining consistent from the 700 °C to 900 °C range. The Al 2 O 3 layer is nanocrystalline, but not as thick or as uniform in composition as that observed in high-temperature steam environments. Notably, the Al 2 O 3 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 Al 2 O 3 layer.