Amorphous and partially-amorphous metal coatings for corrosion resistance in molten chloride salt

Abstract

Amorphous metal coatings were developed to improve the corrosion resistance of structural alloys in molten salts for use as salt-facing materials in concentrating solar power (CSP) and molten salt reactor (MSR) applications. Three coatings were tested. One Fe-based, fully amorphous coating, and two Ni-based partially amorphous coatings. The candidate coatings were applied to samples made from Ni-based alloy 230, and exposed to KCl–MgCl2 at 750 °C for 300 h in sealed Mo capsules. After exposure, uncoated alloy 230 samples were depleted in chromium near the surface, as measured by SEM-EDS. The attack had an average depth of 33 μm. All three coatings performed well, showing no observable degradation during exposure, despite chromium contents between 20% and 40%. XRD and TEM measurements showed the coatings were fully crystallized after exposure, so the excellent corrosion resistance can likely be attributed to the recrystallized microstructure of the coatings.