AlN Coatings on Hastelloy-N Alloy Offering Superior Corrosion Resistance in LiF-KF-NaF Molten Salt

High-temperature corrosion resistance is a big issue for structural materials in molten salt reactors. A simple but effective laser cladding technique has been utilized for producing a compact AlN coating on Hastelloy-N alloy. The results show that the laser-cladded AlN coating improves the compatibility of Hastelloy-N alloy in LiF-NaF-KF molten salt at 900 degrees C significantly. The uncoated Hastelloy-N alloy is composed of gamma-Ni and M6C phases, showing a typical intergranular corrosion with a precipitation of new Cr9Mo25Ni20 phase after corrosion. In contrast, the AlN coating exhibits a silghtly unifrom corrosion and protects the Hastelloy-N substrate effectively. The laser-cladded specimes are composed of gamma-Ni and AlN before and after corrosion. The possible reasons for the discrepancy in the corrosion behavior between uncoated and coated specimens are discussed in this job.