Oxidation Characteristics of Two FeCrAl Alloys in Air and Steam from 800A°C to 1300A°C

Iron-chromium-aluminum (FeCrAl) alloys are being investigated as cladding material for urania nuclear fuel in light water power reactors. One extraordinary attribute of the FeCrAl alloys is their resistance to attack by air and steam up to their melting point. It was of interest to study the kinetics of oxidation of FeCrAl from 800A degrees C to 1300A degrees C in air and in steam to determine how the oxides evolve to provide protection to the alloys. The two investigated alloys were APMT (Fe-21Cr-5Al-3Mo) and C26M (Fe-12Cr-6Al-2Mo). Results show that both alloys had similar oxidation kinetics despite their different chemical compositions. For the testing times, the oxidation rate was higher in air than in steam at the higher temperatures (1100-1300A degrees C) and higher in steam than in air at the lower temperatures (800-1100A degrees C). In the lower temperature range, the surface oxide consisted of two layers, an internal layer rich in aluminum and an external layer containing Al, Cr, and Fe. In the higher temperature range, the oxide was a single layer of alumina (no Cr, no Fe, no Mo).