Abstract
Selective oxidation of Fe–25Ni–20Cr–xAl-based alloys under low oxygen pressure was studied to improve oxidation and coking resistance. The morphology and oxidation kinetics of the oxide layer were analyzed using multi-scale techniques such as scanning electron microscopy, electron probe micro-analysis, and X-ray photoelectron spectroscopy. The results indicated that when the Al content exceeded 2.5 wt%, a duplex-structure oxide film, mainly consisting of M2O3 (M: Al and Cr) outer and Al2O3 inner layer, was formed on the surface of the alloy after pre-oxidation. When the Al content exceeded 8 wt%, a complete and dense Al2O3 external oxide film was formed through a two-step oxidation process. The decrease in oxygen partial pressure and surface enrichment of aluminum during the pre-oxidation process accelerated the formation of an external Al2O3 oxide film. Therefore, it isolated the catalytic coking reaction of Fe and Ni transition metals in the alloy with the pyrolysis atmosphere, significantly improving the anti-coking performance of the alloy.
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