Corrosion Resistance of Thermal Spray Coatings in an FLiNaK Melt

A protective coating deposited by high-velocity oxygen fuel (HVOF) spraying is used to improve the corrosion resistance of structural materials in molten salts. Austenitic 12Kh18N10T stainless steel and a KhN62M-VI nickel alloy are studied. A self-fluxing nickel-based PG-12N-01 powder is a base material for an HVOF coating, which was subjected to additional remelting with an acetylene torch to decrease porosity. Corrosion studies are conducted under static conditions in an FLiNaK melt at 650°C for 100 h. The corrosion rates were calculated using gravimetric and chemical methods. The results of corrosion tests demonstrate that the coating significantly decreases the corrosion rate of 12Kh18N10T steel, from 288–294 to 85–93 μm/year, and the effect for the KhN62M-VI alloy is less pronounced, from 85–91 to 76–79 μm/year. Microstructural analysis demonstrates that the coatings are dense and homogeneous, through porosity is absent, and defects are rare; however, local signs of selective dissolution of individual phases are detected. The obtained results confirm the feasibility of using nickel-based HVOF coatings for protecting materials in the FLiNaK melt, and further investigations should be aimed at optimizing the phase composition of the resulting composite material and at reducing the susceptibility of the coating to selective corrosion.