Corrosion Resistance of Hastelloy G-35 Nickel-Based Superalloy in Various Aggressive Media

Abstract

Nickel-based superalloys are widely used in various fields of engineering and technology in contact with aggressive liquid media. High-temperature molten salts are one of the types of such corrosive liquids. Molten electrolytes are widely used in technologies for the electrowinning and refining non-ferrous and rare metals, in nuclear industry and solar storage systems. In the present study the corrosion resistance of Hastelloy G-35 Аlloy (UNS N06035) nickel-based alloy was investigated. Corrosion properties of the material were examined in NaCl–KCl melt at 750 °C under inert (Ar) and oxidizing (air) atmosphere, and in acidic KCl–AlCl3 melts under an inert atmosphere (Ar). KCl–AlCl3 melts were chosen in addition to NaCl–KCl as having higher oxidation ability. Samples were kept in contact with the melts for 30 h. Additional corrosion tests were performed in a boiling sulfuric acid solution in the presence of iron (III) sulfate (according to the ASTM G28-02A procedure) and these lasted for 120 h. The corrosion rates of the alloy samples in various molten media were calculated and are given in Table 1. The slowest corrosion was observed in NaCl–KCl melt under an inert atmosphere. The corrosion rate in NaCl–KCl melt increased noticeably in the presence of oxygen in the atmosphere, and the corrosion resistance of the alloy under these conditions was low. The rate of the alloy corrosion in KCl–AlCl3 melt at 750 °C was extremely high, and this alloy cannot, therefore, be recommended for application as a construction material in this melt under the conditions studied. The data obtained were compared with results of corrosion tests performed according to the ASTM G-28-02A standard. Samples of Hastelloy G-35 alloy were examined in the initial state and after preliminary aging in KCl–AlCl3 at 650 °C for 200 hours (Table 2). The corrosion rate of the alloy in boiling sulfuric acid solution in the presence of iron (III) sulfate was comparable to that in the NaCl–KCl melt under an inert atmosphere. Preliminary aging in the KCl–AlCl3 melt led to intensification of the corrosion processes in aqueous solutions. Figure 1