Selective Cr dissolution and redistribution in Fe-Cr during localized FLiNaK salt exposure

Abstract

Understanding the atomic-scale origins of corrosion in molten fluoride salt environments is essential for developing resilient materials for advanced nuclear and energy systems. Here, we investigate the response of an epitaxially grown Fe-8Cr alloy film to localized FLiNaK salt exposure to elucidate early-stage degradation mechanisms. High-resolution scanning transmission electron microscopy (STEM) and atom probe tomography (APT) reveal localized salt ingress, selective Cr depletion from the alloy, and Cr enrichment near the salt-affected region. APT further shows salt-metal intermixing and enhanced Cr-F chemical association, consistent with the greater thermodynamic stability of Cr fluorides relative to Fe fluorides. These observations suggest that Cr redistribution modifies local salt-metal interfacial chemistry during early-stage corrosion. Atomic-scale observations further show lattice rotation and partial coherency between solidified salt and metallic lattice. This approach provides new insight into atomic-scale corrosion phenomena and establishes a foundation for understanding how evolving interfacial chemistry governs corrosion progression in structural alloys.