Unraveling high-temperature corrosion mechanisms of eutectic high-entropy alloys in molten MgCl2-NaCl-KCl

• A systematic comparison of eutectic HEAs in molten salts was investigated. • CoCrFeNiMo 0.8 exhibits markedly superior long-term corrosion resistance. • Mo-enriched dendritic barriers impede molten salt infiltration and Cr migration. • Preferential dissolution of Al in AlCrFeNiMo 0.2 accelerated Cr depletion. • Alloy design strategy in HEAs enhances corrosion resistance for CSP applications. In concentrated solar power (CSP) systems, molten chloride salts present substantial corrosion challenges for structural materials, where high-entropy alloys (HEAs) show promise due to their unique properties. Two eutectic high-entropy alloys, AlCrFeNiMo 0.2 and CoCrFeNiMo 0.8 , were designed based on the Fe-Cr-Ni system by substituting Al with Co to improve thermal stability while increasing Mo content for enhanced corrosion resistance. The corrosion mechanisms of two alloys were comparatively investigated in molten MgCl 2 -NaCl-KCl (60-20-20 mol.%) at 700 °C. Results show that the corrosion rate of AlCrFeNiMo 0.2 is 4809.92 μm/a, whereas that of CoCrFeNiMo 0.8 is only 73.03 μm/a, indicating a remarkable improvement in corrosion resistance. In AlCrFeNiMo 0.2 , the high electrochemical activity of Al causes intense dissolution of the Al-rich B2 phase, triggering the synergistic dissolution of Cr and the formation of corrosion pits. In contrast, CoCrFeNiMo 0.8 exhibits excellent long-term corrosion resistance, attributed to its homogenous microstructure and elemental distribution. A dense dendritic barrier forms through the enrichment of Mo in CoCrFeNiMo 0.8 , effectively preventing the infiltration of molten salt and the migration of Cr. These findings provide a theoretical basis for designing HEAs with improved corrosion resistance in molten salt environments.