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

Abstract

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 high-temperature 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 -Al 2 O 3 formed from beginning of oxidation on the alloy with higher Fe ratio, but metastable Al 2 O 3 formed on the alloy with lower Fe ratio, and it remained longer when alloy Fe ratio was decreased. The effect of Fe on promoting -Al 2 O 3 formation is explained due to initial formation of -Fe 2 O 3 , which has isomorphous structure with -Al 2 O 3 . The additional effect of Fe on the growth rate ofAl 2 O 3 was also discussed.

CHAPTER 4 High Temperature Oxidation of Stainless Steels

“…Fig. 4.9 shows the phase transformation behaviour of Al2O3 scale which formed on Fe-41.5Al (at.%), Ni-41Al-41Fe (at.%) and Ni-41.5Al (at.%) [44]. It was found that high iron content is beneficial and promotes the rapid transformation to α-Al2O3.…”

“…From the previous studies, the template effect is interpreted as a precipitation of α-Al2O3 from the transient Fe2O3 with Al2O3 saturation [35,[40][41][42][43]. Hayashi et al [44] studied the meta-stable phase transformation behaviour of Al2O3 scale on Fe-Ni-Al alloys. They found that the oxidation mass gain tended to be reduced with the increased iron content in the alloy.…”