The Oxide Scales Formed on a Dispersion-Strengthened Powder Metallurgical FeCrAl Alloy at 900 °C in O2 and in O2 + H2O

Early oxide scale growth on an oxide dispersion strengthened rapidly solidified powder FeCrAl material, Kanthal(A (R)) APMT, was investigated at 900 A degrees C in an O-2 + N-2 and an O-2 + H2O + N-2 environment for up to 168 h. Gravimetry was used to follow oxide growth and the oxide scale was examined with XRD. Scale morphology was investigated in detail with SEM/EDX, TEM/EDX/CBED. The alloy rapidly formed a protective two-layered alpha-alumina scale containing oxide nodules. Between the top and bottom alumina layers there was a zone containing chromia-rich particles 5-20 nm in diameter, corresponding to the original sample surface. The alumina scale mainly grew inward after 1 h of oxidation. Alumina scale growth at 900 A degrees C was initially somewhat faster in an O-2 + H2O + N-2 environment than in an O-2 + N-2 environment.