Formation of chromium-iron carbide by carbon diffusion in AlXCoCrFeNiCu high-entropy alloys

Effect of the addition of carbon on phase formations in AlxCoCrFeNiCu (x = 0.3, 1.5, 2.8) high-entropy alloys (HEAs) was studied. Free diffusion of carbon from graphite crucible resulted in the partitioning of the entire Cr from the matrix and the formation of the (Cr,Fe)23C6 phase in all HEAs. No other metal-carbide phase was detected. The formation of (Cr,Fe)23C6 enhanced the overall hardness of the HEAs. By increasing the amount of Al, the Cr amount decreased resulting in the reduction of carbon diffusion and volume fraction of the (Cr,Fe)23C6 phase in HEAs. The hardness of matrix phases and the overall hardness of HEAs increased with an increase in the amount of Al.Impact statementThe detailed phase analysis reveals that C addition to AlxCoCrFeNiCu HEAs leads to the formation of the (Cr,Fe)23C6 phase. The overall hardness can be controlled by the amount of C and/or Al.