Oxidation Behavior of Nanocrystalline and Coarse-grain Fe-0.5Si Alloys

The oxidation behavior of nanocrystalline (NC) Fe-0.5Si alloy prepared by mechanical alloying was investigated at 900 ℃ and 1 000 ℃ in flowing pure oxygen of 1 atm,and was compared to the oxidation behavior of coarse-grain (CG) Fe-0.5Si alloy prepared by conventional casting under the same treatment condition.At the two temperatures,both Fe-0.5Si samples formed similar complex external scales composed of Fe2O3,Fe3O4,FeO and SiO2.Compared to CG Fe-0.5Si,NC Fe-0.5Si had more grain boundaries,which acted as high-diffusivity paths and promoted the outward diffusion of Fe and the inward diffusion of oxygen,so the oxidation rate was increased significantly.Although the volume percent of SiO2 in the mixed oxides of FeO+SiO2 of NC Fe-0.5Si was higher than that of CG Fe-0.5Si,the absolute diffusion rates of Fe and oxygen still increased.Nanocrystallization decreased the high-temperature oxidation resistance of Fe-0.5Si alloy.