Oxidation and hot corrosion behaviors of Nb−Si based ultrahigh temperature alloys at 900 °C

Abstract Oxidation and hot corrosion behaviors at 900 °C of Nb−Si based ultrahigh temperature alloys were investigated. Both oxidation and hot corrosion kinetics curves of the alloy involve an initial parabolic stage and a later rapid linear stage. In the initial oxidation stage (1−50 h), a thin and continuous scale is formed on the alloy surface, while severe pest degradation phenomenon is observed in the linear oxidation stage. Compared with oxidation of the alloy in static air, a linear hot corrosion stage happens earlier and catastrophic scale disintegration occurs after hot corrosion for 20−100 h, demonstrating that molten salts (Na2SO4 and NaCl) could significantly accelerate the oxidation process of the alloy. STEM results indicate that the corroded scale consists mainly of TiO2, Nb2O5, TiNb2O7, amorphous silicate and NaNbO3.