The corrosion behavior of the corrosion-resistant alloy Hastelloy G-35 (manufactured by Haynes International, Inc.), corrosion and heat resistant alloy VDM Alloy 600 or Nicrofer 7216 and corrosion-resistant alloys VDM Alloy C-4 or Nicrofer 6616 and VDM Alloy 625 or Nicrofer 6020 (all produced by VDM Metals) was studied at 450-650 °C in fused KCl-AlCl3 mixture with the initial AlCl3-to-KCl ratio of 1.1. Time of exposure varied from 6 to over 1000 h. The corrosion rates of all the nickel-based alloys studied were determined by the red-ox processes resulting in dissolving the most electronegative alloy components (Cr, Fe and Mn) indicating that the processes taking place had electrochemical nature. Increasing temperature led to a noticeable increase of corrosion rates and a change of the corrosion process nature. Transmission electron microscopy revealed that intermetallic phases (such as sigma-phase in case of Hastelloy G-35 and Alloy 625 or Ni2(Cr,Mo) secondary phase in VDM Alloy C-4) can be formed during prolonged high-temperature exposure. These phenomena can accelerate the processes of intergranular corrosion and stress corrosion cracking of studied materials in industrial conditions. The results obtained agreed well with thermodynamic analysis, mechanical and thermophysical properties of the alloys and constructed "time-temperature-precipitation" diagrams.

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The corrosion resistance of Haynes 230, Hastelloy S and X hightemperature alloys and Hastelloy N, B-3, G-35, C-2000 corrosionresistant alloys was investigated in a wide temperature range (450-650 °C) in fused KCl-AlCl 3 mixtures. It was found that the mechanisms of corrosion of high-temperature alloys and corrosionresistant alloys in KCl-AlCl 3 based melts are different. At a critical temperature phase structure of the high-temperature alloys changes after contact with chloroaluminate melts resulting in formation of intermetallic or carbon-containing phases along the grain boundaries that result in increasing strength of the alloys but initiate intense intergranular corrosion. The structural changes in most of the corrosion-resistant alloys take place at higher temperatures but they also can cause structural changes in the materials. It was shown that both types of alloys undergo intergranular corrosion up to the critical conditions. Formation of different secondary phases was detected and their influence on the corrosion processes mechanism is analyzed.

The corrosion of KhN65MVU alloy was studied in chloride melts contained vanadium, zirconium, niobium and uranium ions and the rates of corrosion were determined for different electrolytes and temperatures. It was shown that interaction between the studied alloy and chloride melts containing transition metal ions occurs due to the oxidation of more electronegative components of the alloy by different cations from the molten salt environment. The process of oxidation is intensified at the grain boundaries where the microgalvanic pairs are formed as a result of excessive phase segregation. Anodic elements of the galvanic pairs are represented by depletion in molybdenum zones contacted with the excessive phases. It was also found that contacting KhN65MVU with niobium-containing melts results in the formation of diffusion coating on the substrate. This coating can protect the material from further oxidation by molten chloride electrolyte.