Metastable-stable phase transformation behavior of Al2O3 scale formed on Fe-Ni-Al alloys

Abstract

The oxidation behavior of Ni-Fe-41.5Al alloy with different Fe/Ni ratio was investigated in air at 1000°C using in-situ higherature X-ray diffraction study by means of Synchrotron radiation. The oxidation mass gain of alloys decreased with increasing Fe content, particularly initial oxidation mass gain significantly decreased with increasing alloy Fe content. In-situ X-ray diffraction study indicated that the stable α-Al2O3 formed from beginning of oxidation on the alloy with higher Fe ratio, but metastable Al2O3 formed on the alloy with lower Fe ratio, and it remained longer when alloy Fe ratio was decreased. The effect of Fe on promoting α-Al2O3 formation is explained due to initial formation of α-Fe2O3, which has isomorphous structure with α-Al2O3. The additional effect of Fe on the growth rate of α-Al2O3 was also discussed.