Nanocrystalline structure remarkably enhances oxidation resistance of Fe-20Cr-5Al alloy

The present study investigates the oxidation behavior of nanocrystalline (NC) and microcrystalline (MC) Fe-20Cr-5Al alloys at 900 ºC. A protective layer of Al2O3 layer is formed at a relatively lower Al content in the case of microcrystalline Fe-Cr-Al alloys containing sufficient amounts of Cr (i.e. third element effect). The required critical content of Al for the formation of a full-fledged Al2O3 layer can further be reduced by the nanocrystalline structure. We demonstrate here that nanocrystalline Fe-20Cr-5Al alloy becomes capable of developing a protective layer of Al2O3. The results show that nanocrystallization presumably reduces the Al requirement below that is necessary for the “third element effect” of Cr. Consequently, the nanocrystalline Fe-20Cr-5Al alloy oxidized at an insignificant rate (c.f., its microcrystalline counterpart). Accordingly, the NC Fe-20Cr-5Al alloy follows logarithmic oxide growth kinetics, whereas the MC Fe-20Cr-5Al alloy follows parabolic kinetics. Additionally, the MC alloy exhibits four times higher weight gain than the NC alloy after 60 h of oxidation.