Effect of C content and annealing on dendrite structure evolution and corrosion resistance of CoCrFeMnNi alloys

In this study, a series of CoCrFeMnNiCx (0–0.8 at% C) high-entropy alloys (HEAs) were prepared by vacuum arc melting and subsequently vacuum annealed at 800°C or 1000°C for 120 h. The aim was to investigate the microstructure evolution and corrosion behavior of the as-cast and annealed CoCrFeMnNiCx alloys in a neutral corrosion solution. Experimental results revealed that the addition of C can refine the as-cast dendrite structure, with an optimal C content of 0.4 at%. Annealing treatment led to a decrease in C solubility in the face-centered cubic (FCC) phase, resulting in the precipitation of carbides. In a 3.5 wt% NaCl neutral solution, the as-cast alloy containing 0.4 at% C exhibited the highest corrosion resistance. After annealing at 1000°C, the alloy's pitting potential and corrosion resistance were further improved. The corrosion behavior of both the as-cast and annealed CoCrFeMnNiCx alloys was primarily composed of pitting and intergranular corrosion, although the dominant mechanism varied among these alloys. This study establishes a correlation between microstructure evolution and corrosion behavior, providing insights for the design of high-entropy alloys with superior corrosion resistance.