Effect of the addition of carbon on phase formations in Al

x

CoCrFeNiCu (

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)

23

C

6

phase in all HEAs. No other metal-carbide phase was detected. The formation of (Cr

Fe)

23

C

6

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)

23

C

6

phase in HEAs. The hardness of matrix phases and the overall hardness of HEAs increased with an increase in the amount of Al.

Impact statement

The detailed phase analysis reveals that C addition to Al

x

CoCrFeNiCu HEAs leads to the formation of the (Cr

Fe)

23

C

6

phase. The overall hardness can be controlled by the amount of C and/or Al.