Effect of carbon content on microstructure, hardness and wear resistance of CoCrFeMnNiCx high-entropy alloys

A set of CoCrFeMnNiCx (x = 0, 0.3, 0.6, 0.9, 1.2) high-entropy alloys (HEAs) were prepared using mechanical alloying and spark plasma sintering. The influence of carbon content on the microstructure, hardness, scratch resistance and wear resistance of the CoCrFeMnNiCx HEAs was systematically investigated. The results show that the CoCrFeMnNiCx HEAs have a dual-phase structure comprised of FCC and M7C3 phases. The M7C3 phase content and porosity are found to increase with increasing the carbon content. The hardness of the HEAs is significantly enhanced by carbon alloying from 327.8 HV for CoCrFeMnNi to 566.4 HV for CoCrFeMnNiC0.6. The M7C3 phase content and porosity are two competing factors that affect the hardness. The CoCrFeMnNiCa6 exhibits the highest scratch and wear resistances of the prepared samples. The wear rate of CoCrFeMnNiC0.6 (0.47 x 10(-5) mm(3)/N.m) is more than an order magnitude lower than that of the CoCrFeMnNi (6.5 x 10(-5) mm(3)/N.m) and is of the same magnitude with the mating material Si3N4. This is due to the precipitation of hard M7C3 carbides and low porosity. The scratch and wear resistances are positively correlated with the hardness. Both delamination wear and abrasive wear contribute to the wear of CoCrFeMnNiCx HEAs. (C) 2020 Elsevier B.V. All rights reserved.