Effect of C additions to the microstructure and wear behaviour of CoCrFeNi high-entropy alloy

CoCrFeNi high entropy alloys (HEAs) suffer from inferior hardness and low wear resistance. The introduction of hard particles is a common strategy to improve the tribological properties of this kind of alloy. However, the influence of carbide type (M23C6, M7C3, and M3C2) and its volume fraction on wear resistance is still under debate. In this work, (CoCrFeNi)100-XCX (x = 0, 1.3, 1.7, 3.5, and 5.4 at. %) HEAs were prepared by vacuum arc melting. M23C6 precipitated in the FCC matrix through a subsequent heat treatment process. The effect of carbon additions on the microstructural evolution and wear behavior of (CoCrFeNi)100-XCX HEAs was investigated by dry sliding experiments with Al2O3 ceramic balls as counterparts. The results show that the C interstitials increased the lattice constant of the FCC matrix, on the other hand, the size and volume fraction of carbide precipitates increased with the carbon content. The Cr23C6 precipitates appeared at the grain boundaries and interdendritic regions, which is believed to help strengthen the alloy, leading to an increase in its hardness and wear resistance. However, when the C content is greater than 0.28 wt %, the wear rate went up due to the poor toughness and severe three-body abrasive wear.