Comparative Study on Oxidation Behavior of Fe-5wt% Cr Alloy in Various Mixed Atmospheres at 900–1 000 °C

Abstract

The high-temperature oxidation behavior of Fe-5wt% Cr alloys was investigated in both N₂+5vol% H₂O and N₂+21vol% O₂+5vol% H₂O atmospheres at 900–1000 °C for 120 min by the thermogravimetric analysis (TGA). The oxidation kinetics, phase composition and cross-sectional microstructure of the oxide scale were contrastively analyzed in both environments. Also, the phase composition of oxide scale was measured by X-ray diffraction (XRD). The cross-sectional microstructure and the interface elements distribution were studied by electron probe microanalysis (EPMA). The experimental results demonstrated that the growth rate and the mass gain of the oxide scale in the N₂+5vol% H₂O atmosphere were both significantly lower than the growth rate and the mass gain in the N₂+21vol% O₂+5vol% H₂O atmosphere. The apparent layer structure of the oxide scale could be observed in an oxygen-enriched environment and did not appear in a pure water vapor without oxygen. In addition, the inner oxide layer growth mechanisms and the outward diffusion of the metal cations were introduced in the atmosphere of N₂+5vol% H₂O. Consequently, the effects of temperature and humid atmosphere on the Fe-Cr spinal scale evolution were also discussed.

Keywords

Fe-5wt% Cr alloy / humid environment / oxidation kinetics / oxide scale / ionic diffusion