Abstract: Carbonate molten salts exhibit higher operating temperatures and greater thermodynamic efficiency than nitrates; however, they also possess stronger oxidizing capacity, which exacerbates corrosion and compromises material durability. Heat-resistant Cu-Ni-Al alloys are promising candidates for sealing and drivetrain components in molten salt systems due to their good microstructural stability and oxidation resistance. This study presents the first application of the Cu₇₅Ni_18.75Al_6.25 (at.%) alloy in high-temperature carbonate salt environments. Furthermore, two novel alloys, Cu_71.86Ni_12.5Al_4.69Co_4.69Fe_3.29Ti_1.56Cr_0.94Zn_0.47 and Cu₇₅Ni_12.5Al_4.69Co_3.125Fe_2.1875Ti_1.56 Cr_0.625Zn_0.3125, were developed and fabricated using a cluster formula compositional design approach. All three alloys exhibited surface-limited oxidation with intact oxide scales after 504 h of continuous exposure at 650 °C. The multicomponent alloys demonstrated significantly lower mass losses (12.96 and 21.18 mg/cm²) and corrosion rates (0.27 and 0.44 mm/year) compared to the Cu₇₅Ni_18.75Al_6.25 (42.46mg/cm² and 0.88 mm/year), indicating the considerable potential of these alloys for use in corrosive molten salt environments. Mechanistic analyses reveal that three primary mechanisms contribute to the superior performance: (i) a high volume fraction of finely dispersed γ' phase, which promotes early and stable Al₂O₃ formation; (ii) multielement segregation at grain boundaries that suppresses intergranular oxidation; and (iii) enhanced solute interactions within the γ/γ' phases, which reduce elemental diffusion. These findings provide clear insights into the corrosion behavior of Cu-Ni-Al-based alloys in carbonate molten salts and offer valuable guidance for the development of high-performance materials suitable for demanding environments.

Key words: Heat-resistant copper alloys, Molten carbonate corrosion, High temperature oxidation, Multicomponent composition design, Corrosion resistance mechanism