Abstract
This study examined both theoretically and experimentally the oxidation behavior of AlCoCr0.5Fe2.5Ni2.5 and Al0.25CoCrFeNi alloys in the time for 10 h and 180 h at 800 °C in air atmosphere. The results showed that the weight gain of the dual-phase AlCoCr0.5Fe2.5Ni2.5 alloy followed the parabolic rate law, while this value persisted almost unchanged for the single-phase Al0.25CoCrFeNi alloy at the same oxidizing condition. Surface analysis of the oxide scale confirmed the formation of Al2O3, Cr2O3 and Fe3O4 oxides. Comparing the experimental results with thermodynamic models and Density functional theory (DFT) calculations suggests that Al and Cr are first oxidized in the AlCoCr0.5Fe2.5Ni2.5 and Al0.25CoCrFeNi alloys, respectively, then outer Fe3O4 scale appeared in the two alloys. The weak resistance to high temperature oxidation of AlCoCr0.5Fe2.5Ni2.5 alloy was mainly ascribed to its high fraction of grain and phase boundaries, as well as the fragmented oxide layer formed due to enhanced element diffusion at the FCC/BCC phase boundaries. The element migration and oxidation process of oxide layers in the two alloys were declared based on thermodynamic and DFT calculations.
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