Accelerated corrosion of Ni-based alloys in molten chloride salts, due to Ni2Cr phase formation

Abstract

To understand how the precipitation of long-range ordering (LRO) in alloys affects molten salt corrosion, two Ni-Cr model alloys—one in as-received (AR) condition, the other isothermally aged to contain MoPt2-type Ni2Cr-ordered precipitates, and both featuring the same Ni-33at%Cr composition—were tested for 500 hours in molten NaCl–MgCl2 salt at 550°C. Post-corrosion weight loss analysis and advanced microstructural characterization of the corroded alloys revealed (through comparison with the AR specimens) that the ordered phase significantly accelerated the corrosion process. This suggests that the loss of Cr atoms in the corroded Ni2Cr-ordered superlattice structure, which creates extra weakness for molten salt corrosion. In terms of high-temperature corrosion resistance, the results of this study emphasize the importance of phase stability when designing alloys for molten-salt applications.