Minyi Zhang, Weiyue Zhou, Michael P. Short, Paul A. J. Bagot, Michael P. Moody, Felix Hofmann
Abstract Understanding corrosion mechanisms in liquid metal-cooled nuclear systems is essential for effective corrosion control. While much literature exists detailing corrosion rates and mechanisms of structural materials in liquid metals, much still remains to be discovered in new regimes of temperature, chemistry, and impurity content. We focus specifically on investigating how liquid lead-bismuth eutectic (LBE) corrodes ferritic/martensitic steels under high-temperature oxidizing conditions. We find that the corrosion is determined by whether a protective oxide layer is formed on the surface. The area without a continuous and dense protection layer experiences oxidation along martensite grain boundaries (GBs), transitioning from intergranular attack to a wider area corrosion, which contains not only GBs but also grains as it progresses. The area with a stable, coherent oxide scale will slow the corrosion process and then is oxidized along recrystallized grain boundaries. Both chromium and oxygen diffusion play vital roles in this process. A Fe-enriched body-centred cubic phase formed on the surface of LBE-corroded T91, contrasting with previous reports that identified oxide-based surface layers with structures closer to face-centred cubic.