Study On High Temperature Oxidation Resistance Of Fe-Al Intermetallic Compounds

The development of combination property of modern advanced superalloys in service is becoming more and more important, such as high temperature strength and chemical stability. In this paper, in order to select the suitable materials of carbonization furnace used in garbage cremation, the high temperature oxidation behavior of Fe-Al intermetallics with different composition is investigated. Moreover, the effect of the addition of minute rare earth element yttrium on oxidation is also investigated. The result is of great importance for establishing the basic high temperature oxidation theory of Fe-Al intermetallics and for the development of promising candidates for carbonization furnace.The isothermal oxidation behavior of Fe-30A1, Fe-35A1 and Fe-40A1 were investigated at 700,800 and 900 ℃. Fe-40Al presents the smallest mass gain at 700 and 900 ℃, corresponding to the value of 0.0776 mg/cm2 and 0.335 mg/cm2 respectively, while Fe-35A1 presents the smallest mass gain at 800 ℃, corresponding to the value of 0.162 mg/cm2. In the case of cyclic oxidation, Fe-35A1 presents the smallest mass gain at 700 ℃, corresponding to the value of 0.0732 mg/cm2, while Fe-40A1 presents the smallest mass gain at 800 ℃, corresponding to the value of 0.127 mg/cm2. The scales formed on Fe-Al intermetallics are composed of an outer protective layer of Al2O3 and an inner layer of Al2O3 and Fe2O3.The isothermal oxidation behavior of Fe-40Al containing about 0.05,0.1 and 0.3 at.% Y was investigated at 700,800 and 900 ℃ respectively. Moreover, the cyclic oxidation behavior of Fe-40Al at 700 and 800 ℃ was also investigated. The addition of rare earth element yttrium in the range of 0.05-0.3 at.% Y can reduce the oxidation rate of the alloy to some extent. In the case of isothermal oxidation, the oxidation resistance improved most obviously for Fe-40Al-0.3Y at 900 ℃, with the value of 0.147mg/cm2, which was about only half of that without the addition of Y. While in the case of cyclic oxidation, the oxidation resistance improved most obviously at 800 ℃, with the value of 0.0623mg/cm2, which was also about half of that without the addition of Y. The addition of Y promotes the formation of the protective Al2O3 layer, and at the same time enhances the adhesiveness of the scale.The isothermal oxidation of Fe-40Al containing about 0.5 at.% Y was investigated at 700,800 and 900 ℃ respectively. Moreover, the cyclic oxidation of that alloy at 700 and 800 ℃ was also investigated. The results showed that the Fe-40Al oxidized more quickly than the alloy without the addition of Y. The addition of rare earth element yttrium in excess is harmful to the formation of a protective layer.