High‐Temperature Corrosion Behavior of Al _0.3 CoCrFeNi and AlCoCrFeNi High‐Entropy Alloys in Na ₂ SO ₄ ‐K ₂ SO ₄ Salt Films

ABSTRACT The high‐temperature corrosion behavior of Al 0.3 CoCrFeNi and AlCoCrFeNi high‐entropy alloys is evaluated at 900°C for 100 h in a Na 2 SO 4 ‐25 wt.% K 2 SO 4 molten salt environment. Corrosion kinetics are determined through mass change measurements, and the corrosion products are characterized using X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. Electrochemical impedance spectroscopy is employed to investigate corrosion mechanisms and the role of aluminum content. AlCoCrFeNi exhibits significantly lower mass loss, attributed to the formation of a dense, continuous Al 2 O 3 scale that inhibits internal oxidation and sulfidation. The presence of Warburg impedance in the EIS spectra indicates a diffusion‐controlled process, with Al 2 O 3 dissolution acting as the rate‐limiting step. In contrast, Al 0.3 CoCrFeNi undergoes severe degradation due to oxide layer disruption, driven by molten salt penetration and extensive scale spallation.