Effect of NaCl‐Na ₂ SO ₄ on the Hot Corrosion Behavior of Nickel‐Based Alloys at 800°C Under Simulated High‐Chlorine Coal Combustion Condition

ABSTRACT The hot corrosion behavior of nickel‐based alloys was investigated under conditions simulating high‐chlorine coal combustion, using a high‐temperature molten NaCl–Na 2 SO 4 (15/85 wt.%) environment at 800°C for 400 h. Severe degradation occurred due to the synergistic effects of chloride‐ and sulfate‐induced corrosion. Chloride species promoted selective chlorination and volatilization of reactive alloying elements, while sulfate decomposition supplied oxygen and sulfur, driving concurrent oxidation and sulfidation. As a result, a characteristic three‐layer corrosion product film developed, consisting of an outer porous oxide layer rich in Ni, Cr, and Ti, an intermediate dense Al 2 O 3 ‐rich layer, and an internal oxidation zone at the substrate interface. The Al 2 O 3 inner layer exhibited strong adhesion and initially provided effective protection against scale spallation; however, defects and discontinuities enabled the inward diffusion of corrosive ions, leading to internal oxidation and localized sulfidation of the substrate.