Abstract: Background: Corrosion of the structural materials of Molten Salt Reactor (MSR) has been recognized as a challenge that prevents the MSR from long term operation. Oak Ridge National Laboratory (ORNL) has revealed that corrosion occurs predominantly through dealloying of Cr from the candidate nickel-based high temperature alloys. Therefore, a systematic study on the corrosion characteristics of candidate structural materials is needed to ensure their applications in MSR. Purpose: The present work is to evaluate the corrosion behaviors of some nickel-based alloys with different Cr content as well as to supply more corrosion data of materials in molten fluoride salts for reliable selection of structural materials. Methods: Static corrosion tests of five kinds of nickel-based high temperature alloys (Hastelloy B-2, Haynes 242, Hastelloy S, GH 3030 and Hastelloy X) were performed in purified molten FLiNaK salt at 700 °C for 400 h. The microstructural morphology and chemical composition of the samples were examined by Scanning Electron Microscope (SEM) and Electron Probe Microanalysis (EPMA). Results: Hastelloy B-2 and Haynes 242 with low Cr content exhibited better corrosion resistance, while the high Cr-content alloys, GH 3030 and Hastelloy X, exhibited severe corrosion after the corrosion tests. Conclusion: It was found that the corrosion was correlated with the original Cr-content of the alloys, and the weight-loss/area due to corrosion increased with the Cr-content of alloys. When the Cr content of alloys is higher than 20 wt.%, these alloys would suffer severe corrosion in molten fluoride salt environments.

Key words: Nickel-based alloys, FLiNaK salt, Corrosion, Cr