Corrosion Behavior of Superalloys in a LiCl-Li₂O Molten Salt

Abstract

A study on the corrosion behavior of Inconel alloys and Incoloy 800H in a molten salt of LiCl-Li₂O was investigated at 650°C for 24–312 hours in an oxidation atmosphere. The order of the corrosion rate was Inconel 600 < Inconel 601 < Incoloy800H < Inconel 690. Inconel 600 showed the best performance suggesting that the content of Fe, Cr and Ni are the important factor for corrosion resistance in hot molten salt under an oxidation conditions. The corrosion products of Inconel 600 and Inconel 601 were Cr₂O₃ and NiFe₂O₄. In case of Inconel 690, a single layer of Cr₂O₃ was formed in the early stage of corrosion and an outer layer of NiFe₂O₄ and inner layer of Cr₂O₃ were formed with an increase of corrosion time. In case of Incoloy 800H, Cr₂O₃ and FeCr₂O₄ were observed. Most of the outer scale of the alloys was observed to be spalled from the results of the SEM analysis and the unspalled scale which adhered to the substrate was composed of three layers. The outer layer, the middle one, and the inner one were Fe, Cr, and Ni-rich, respectively. Inconel 600 showed localized corrosion behavior and Inconel 601, 690 and Incoloy 800H showed uniform corrosion behavior. Ni improves the corrosion resistance and too much Cr and/or Fe content deteriorates the corrosion resistance.