Mechanisms of molten fluoride salt corrosion of laser powder bed fused 316L stainless steels

Additively manufactured (AM) stainless steels (SS) are under consideration for molten salt reactors. However, molten salt corrosion of AM SS remains poorly understood. Here we present the mechanisms of corrosion of laser-based powder bed fused (LPBF) 316L SS in FLiNaK + 5 wt. % EuF 3 molten salt at 650 °C. Microstructural features of dislocation cells, low-angle grain boundaries, and carbides appear to be the major underlying features influencing corrosion behavior. Corrosion-induced, salt-filled voids follow {100} crystallographic planes rather than AM-induced microstructural features. Dislocation cell structures retain Cr, and yet they appear to slow molten salt corrosion in the long run, with limited grain boundary migration observed. Larger Cr carbides disappear in the salt penetration regions, leaving only Mo carbides. Smaller carbides and remaining high Ni-enrichment layer slow down Cr depletion and molten salt penetration.