The effect of the microstructure on the corrosion behavior of N5 superalloy in a molten (Li,Na,K)F eutectic salt

Abstract

The corrosion of structural materials in molten fluorides, influenced by the microstructure of the structural materials, is considered to be a great challenge for the development of molten salt reactors using fluorides as fuel carriers or coolants. In this paper, the corrosion behavior of the monocrystal and polycrystal N5 superalloy in molten (Li,Na,K)F eutectic salt at 700 °C is investigated. The results indicate that the mass loss of the polycrystal is much higher than that of the monocrystal after immersion in molten (Li,Na,K)F for 100 h. The corrosion of the monocrystal and the polycrystal N5 superalloys occurs mainly through the preferential dissolution of Cr and Al, which leads to an Al/Cr-depleted layer and some internal voids. Furthermore, the corrosion rate of the polycrystal N5 superalloy is obviously accelerated by the existence of grain boundaries, which results in a mass loss of about 16.995 mg cm⁻² and a Al/Cr-depleted layer of around 175 μm, compared to 11.373 mg cm⁻² and 125 μm, respectively, for the monocrystal N5 superalloy.