Influence of the Composition of Nickel Alloys on the Mechanism of Their Corrosion in NaCl–KCl-Based Chloride Melts

Abstract—The influence of the composition of nickel alloys on the mechanism of their corrosion in NaCl–KCl-based chloride melts has been analyzed. Nickel alloys NIMONIC 80A alloy, VDM Alloy 718, INCONEL alloy C-276 with different compositions of the matrix and alloying additives have been selected as the investigated materials. The corrosion rates of these alloys in NaCl–KCl and NaCl–KCl + UCl₄ salt systems after exposure for 100 h at 750°C has been found. It has been shown that NIMONIC 80A alloy containing high-chromium excess phases is subjected to intergranular corrosion after only 30 hours of contact with NaCl–KCl. It has been demonstrated that continuous nonuniform corrosion is the main reason for damage of VDM 718 alloy (which also has excess phases in the microstructure) after 100 h of exposure in NaCl–KCl. Although prominent secondary-phase grain-boundary chainlike precipitates arise in INCONEL C-276 alloy at 750°C, its surface exhibits continuous uniform damage. From data obtained it was concluded that secondary phases arising in VDM 718 alloy and INCONEL C-276 alloy serve as cathodes of galvanic microcouples. Therfore intergranular corrosion (IGC) on the surface of these alloys has not been observed. It has been shown in a series of special experiments that in uranium-containing chloride melt, the corrosion rate rises by many times and the type of surface damage becomes basically the same—continuous nonuniform.