Insights into oxidation and nitridation of alumina-forming FeCrAl alloy after supercritical water exposure: Effect of pre-corrosion on high-temperature damage behavior

This work investigated the corrosion characteristics of FeCrAl alloy in supercritical water (SCW), and focused on the effect of SCW pre-corrosion on the alloy oxidation and nitridation at 900 °C. FeCrAl alloy formed outer Fe-rich oxides (mainly Fe₂O₃) and inner Fe-Cr-Al oxides during SCW exposure. SCW pre-corrosion made FeCrAl alloy exhibit different morphologies and phase compositions in the same medium. SCW pre-corrosion promoted the deposition of Ni and Mo elements from the autoclave, filling the gaps in flaky oxides by forming Ni- and/or Mo-rich products in air and N₂. Moreover, SCW pre-corrosion avoided the appearance of accelerated nitridation zones in N₂. However, pre-corrosion caused the preferential diffusion of N₂ and air. Outward-diffused Cr ions during SCW exposure reacted with O impurities in N₂ to form Cr₂O₃ that easily dissociated N₂, leading to the development of nitridation towards the alloy interior.