Effects of Surface Treatment on Corrosion Resistance of Alloy 825 in Supercritical Water

The effects of three surface treatments including Cr-coating, TiN-coating and acid (wash) passivation on the corrosion resistance of nickel-based alloy Alloy 825 in supercritical water were studied by intermittent high temperature and high pressure reactor. The results show that the corrosion resistance of the alloy samples after surface treatments was better than that of the untreated alloy sample in the same corrosive media, and their corrosion resistance from high to low was ranked as Cr-coating, TiN-coating, acid passivation. In the most corrosive supercritical water containig both chloride and oxygen, the oxidation film on surface of TiN-coated, acid passivated and untreated alloy samples exfoliated seriously, and the oxide of Cr forming on the surface of the Cr-coated alloy sample was dense and stable, so the Cr-coated alloy had the best corrosion resistance. The oxides on the surface of the alloy were mainly composed of Cr₂O₃ and NiCr₂O₄.