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 AlCoCrFeNiCx (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 AlCoCrFeNiCx HEAs. The corrosion resistance of AlCoCrFeNiC0.4 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. •Microstructure and corrosion behaviour of AlCoCrFeNiCx high-entropy alloys studied.•The corrosion resistance of the alloys improved with increasing carbon content.•The inert carbon remaining on the surface of the passive film inhibits corrosion.•Majority of the carbon dissolved the solid solution, which refined the grains.•The carbide Cr23C6 gradually increased with increasing carbon content.