Unraveling Impurity-Dependent Morphological and Chemical Evolution of Ni-20Cr Alloy in Eutectic LiCl-KCl Molten Salt

Understanding the interfacial evolution of alloys in molten salt with different amounts of water (H₂O) and oxygen (O₂) impurities is significant for applications in many fields, including concentrated solar power, molten salt reactors, and applications in pyrochemical reprocessing and electrorefining. Additionally, the impurity-driven corrosion mechanisms that lead to various morphological and chemical evolution characteristics at the interfaces of structural alloys and molten salts are not fully understood. In the present work, the three-dimensional (3D) morphological evolution of Ni-20Cr microwires in LiCl-KCl was studied at 500 °C under different moisture and oxygen conditions using in situ synchrotron transmission X-ray microscopy (TXM) and scanning transmission electron microscopy (STEM) techniques. No significant morphological changes were observed in Ni-20Cr microwires under vacuum conditions. However, the wires exhibited distinct morphological evolutions when exposed to molten salt containing H₂O alone, as well as when both H₂O and O₂ were present. Furthermore, Cr₂O₃ precipitates were observed in the molten salt during corrosion with only H₂O present, while Cr⁶⁺ species were identified in the salt when O₂ was added. These findings are crucial for understanding the corrosion mechanisms of molten salt with different amounts of H₂O and O₂ contamination, providing insights for developing corrosion mitigation methods and improving the stability of containment alloys in molten salt applications.