High-temperature corrosion behavior of Inconel 625 alloy in a ternary molten salt of NaCl-CaCl2-MgCl2 in air and N2

Abstract

Chloride molten salt is a promising material for heat transfer and storage under high-temperature conditions. However, the metal materials in pipes and vessels may corrode when exposed to high-temperature molten salts. Corrosion causes serious safety accidents in commercial concentrating solar power systems. In this paper, the corrosion behavior of Inconel 625 (In625) alloy was investigated by immersing In625 alloy in a ternary molten salt of NaCl-CaCl2-MgCl2 with varying contents of MgCl2 and under various atmospheres at 600 °C for up to 21 days. The results show that chromium dissolution is the main corrosion process of In625 when immersed in the ternary molten salt. The corrosion rate was higher at the beginning of the corrosion process but gradually decreased with increasing corrosion time. This study found that MgO and MgCr2O4 were produced in the corrosion layer. MgO and MgCr2O4 play a key role in preventing corrosion in air. However, the corrosion layer cracks in N2. Thus, MgO and MgCr2O4 cannot play an acceptable protective role. Additionally, this study found that O2, H2O and MgOH+ significantly affect the corrosion behavior of In625 in different atmospheric conditions.