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

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 degrees 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 degrees 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.