Insights into the oxidation behavior of Ni–25Cr–10Fe–xSi (x = 1, 2, 3, 4 wt%) alloys at 1000°C in ambient air

Abstract

The isothermal oxidation behavior of Ni-25Cr-10Fe-xSi (x = 1, 2, 3, 4 wt%) alloys at 1000°C in ambient air was investigated. The thermodynamics and kinetics of the oxidation behavior were analyzed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, Raman spectroscopy, and the Thermo-Calc software with the TTNI8 database. The weight gain per unit area of the four alloys showed a parabolic relationship with the oxidation time. The weight gain of the oxides decreased with the addition of larger amounts of Si from 1 to 3 wt%; however, this trend was lost when excessive addition of Si (4 wt% Si) was added. A sufficient amount of discontinuously distributed SiO 2 precipitates resulted in better oxidation resistance and adhesion properties than continuous SiO 2 layers. The spallation resistance of the oxide scales is believed to be mainly dependent on the distribution of the SiO 2 layer rather than the content of SiO 2 ; 3 wt% is a reasonable reference value for Si addition for improving the oxidation resistance of Ni-25Cr-10Fe alloys.