Oxidation Characteristics and Oxide Layer Evolution of Alloy 617 and Haynes 230 at 900 A°C and 1100 A°C

To evaluate the oxidation resistance of Alloy 617 and Haynes 230, oxidation tests were performed at 900 A degrees C and 1100 A degrees C in air and helium environments. Scale characterizations were assessed on specimens exposed to air using thin-film XRD, XPS, SEM and EDX. Oxidation resistance was dependent on the stability of the surface oxide layer, which can be affected by minor alloying elements such as Ti and Mn. At 900 A degrees C, for Alloy 617, a mixture of the extensive NiO-Cr2O3 double layer and isolated NiO-NiCr2O4-Cr2O3 triple layer were observed at a steady-state condition. For Haynes 230, a MnCr2O4 layer was formed on top of the Cr2O3 layer, resulting in a lower oxidation rate. At 1100 A degrees C, both alloys showed a double layer consisting of an inner Cr2O3 and outer MnCr2O4 or TiO2. The spallation of outer layer and subsequent volatilization of the Cr2O3 layer produced a rugged surface and interface as well as internal oxidation.