This study aims to investigate the impact of Al content (x = 0.1, 0.3, 0.5) on microstructure evolution and hot corrosion resistance of CoCrFeNiAlx high-entropy alloys (HEAs) in molten Na2SO4 + 25 Wt.% NaCl salt at 900°C, and to identify composition-optimized alloys for high-temperature marine applications.
CoCrFeNiAlx alloys with varying Al contents (x = 0.1, 0.3, 0.5) were exposed to hot corrosion in Na2SO4 + 25 Wt.% NaCl at 900 °C for 100 h. Microstructural characterization and corrosion kinetics (weight gain measurement) were coupled with corrosion product analysis via X-ray diffraction and scanning electron microscopy-EDS.
An Alx = 0.5 composition triggered a dual-phase transition from FCC to FCC + BCC with dendritic BCC grains, resulting in an ultra-low weight gain of 9.9 mg/cm2 after 100 h at 900 °C in a Na2SO4-NaCl solution, compared to 31.2 mg/cm2 for Al0.1 and 24.6 mg/cm2 for Al0.3. Corrosion scales showed dual-layer structure: outer (Al2O3 + Cr2O3 + spinel) and continuous inner a-Al2O3 barrier. This dense Al2O3 layer blocked Cl-induced cyclic sulfidation/chlorination by halting molten salt penetration.
This study offers significant insights into the combined effects of Al content on the hot corrosion behavior of HEAs, which is helpful for further study of CoCrFeNiAl HEAs system.
