Influence of Rare-Earth Yttrium on High-Temperature Oxidation Behavior of Fe-Si Alloys

The high-temperature oxidation behavior of Fe-Si-Y alloys has been studied at 1173 and 1273 K in 0.1 MPa flowing pure O-2. Results show that as the content of rare-earth yttrium raises, the grain size of Fe-Si-Y alloys decreases obviously, which increases grain boundaries in the alloys. The grain size of the oxides formed on the grain-fined alloys is also decreased. These enhance the diffusion rate of the alloying elements through the alloy matrix and oxide scales, and promotes the formation of SiO2 and Y2O3. However, a single and continuous SiO2 or Y2O3 scale still does not form on yttrium-containing alloys when being oxidized at 1173 or 1273 K, but their rapid formation and partial lateral connection due to the grain refinement can restrain the element diffusion in the alloys to some extents, and thus the oxidation resistance of the alloys is improved. The mechanism related with the effect of the grain refinement resulting from the addition of rare-earth yttrium on high-temperature oxidation behavior of Fe-Si alloys is also discussed.