2002 Volume 51 Issue 3 Pages 115-122
The high-temperature oxidation behavior of the Fe-X (X=Al, Cr, or Si) alloys in atmospheres containing water vapor and oxygen was investigated using thermo-gravimetry, scanning electron microscopy, electron probe micro-analysis, and X-ray diffraction.
Oxidation amounts of all alloys increased remarkably by addition of the water vapor. The oxidation behavior of each alloys showed S-shaped curves that consisted of three stages: slow-incubation, rapid transition, and relatively slow steady state oxidation. There was a little effect of water vapor in the oxidation of Ni-Cr alloy which was investigated for comparison.
Without water vapor, the oxide scale was composed of a thin triplex structure of Fe2O3, Fe3O4, and Al, Cr, or Si rich protective oxide with internal oxides of the alloying elements. In atmospheres containing water vapor, the scale structure is similar at the incubation period, in the transition period a thick duplex outer scale of iron oxide and an inner porous scale was formed on all alloys. The inner scale was composed of a duplex phase of FeO and FeAl2O4, (Fe, Cr)3O4, or Fe2SiO4.
The results suggested that the change in protective oxide scale to the less protective FeO and complex oxide was caused by increases in oxygen partial pressure at the scale/alloy interface in the atmospheres containing water vapor.
