Zirconium Effect on the Corrosion Behavior of 316L Stainless Steel Alloy and Hastelloy-N Superalloy in Molten Fluoride Salt

A corrosion test was performed on 316L stainless steel alloy (316L) and Hastelloy-N superalloy (Hastelloy-N) at 850°C for 1000 h in static molten fluoride salt, 46.5LiF-11.5NaF-42KF (mol %) with Zr additions. The interactions between the graphite sample and the tested alloys in the molten salt were also analyzed. The results show that Zr addition to the salt caused the deposition of a pure Zr coating on 316L and Hastelloy-N. The formation of this coating was followed by interdiffusion between the Zr deposit and the substrates. A thicker Zr deposit was observed on Hastelloy-N samples compared to 316L due to the larger electromotive potential difference between Ni/Zr than that between Fe/Zr. The interdiffusion subsequent to Zr deposition led to the formation of a coating composed of a Ni/Zr intermetallic phase even on the iron-based 316L. This intermetallic coating on the two alloys acted as a barrier layer for Fe and Cr outward diffusion. Zr₃NiO and ZrO₂ phases were also observed on the coating surfaces and in the coatings, respectively. The graphite sample, on the other hand, had no direct and significant effect on the corrosion behavior of the alloys and the coating formation on the alloys.