Investigating Cr dealloying and Li ingress in Ni-Mo-Cr alloys with different Mo/Cr ratio exposed to FLiNaK salt

Abstract

Ni-Mo-Cr alloys (Hastelloy N and Hastelloy X) having different Mo/Cr ratio were exposed to FLiNaK salt at 973 K for 72 h in an in-house developed static corrosion test facility. Though both the alloys showed non-uniform attack and selective Cr dealloying, Hastelloy X showed enhanced localized corrosion owing to lower Mo/Cr ratio and pre-existing carbides. The carbides act as cathode in the alloy/precipitate micro-galvanic couple thereby accelerating the corrosion in the adjacent alloy surface. Furthermore, Li ingress into these alloys during corrosion was observed for the first time and in case of Hastelloy X, Li was found to form Li2CrO4.