Effect of non-metallic carbon content on the microstructure and corrosion behavior of AlCoCrFeNi high-entropy alloys

The addition of carbon has been reported to improve the corrosion resistance of various alloys. However, few studies have investigated the effect of non-metallic elements on the corrosion behaviour of AlCoCrFeNi high-entropy alloys (HEAs), which are among the most extensively developed alloys and potential alternatives to structural materials. Therefore, herein the microstructure and corrosion behaviour of AlCoCrFeNiC_x (x = 0, 0.1, 0.2, 0.3, and 0.4 in molar ratio) HEAs were studied in a 3.5 wt% NaCl solution. The results show that adding carbon increased the carbide (Cr₂₃C₆) content and reduced the mean grain size. Further, increasing the carbon content improved the stability of the passive film and corrosion resistance of the AlCoCrFeNiC_x HEAs. The corrosion resistance of AlCoCrFeNiC_0.4 HEAs is optimal, and the passive current density is 2.57 μA/cm², which is 0.16 times that of AlCoCrFeNi HEAs without carbon. The corrosion mechanisms of the AlCoCrFeNi HEAs with various carbon contents were also elucidated. The results of this study provide excellent theoretical guidance and experimental basis for the development and application of corrosion-resistant metallic materials.