Synergistic strengthening and toughening of eutectic CxCoCr3Fe5Ni high entropy alloy

CxCoCr3Fe5Ni (x=0, 0.1, 0.2 and 0.3, at.%) high entropy alloys (HEAs) were prepared via vacuum induction melting. The effects of carbon content on the microstructures and mechanical properties of the HEAs were intensively investigated. With the increase of the carbon content, the phase structure transforms from a dual-phase (FCC+BCC) to a eutectic mixture (FCC phase + M23C6 carbide). Compared to CoCr3Fe5Ni base alloy, the C0.2CoCr3Fe5Ni eutectic HEA exhibits a significantly improved yield strength (from 307.5 to 378.9 MPa), ultimate tensile strength (from 646.5 to 837.1 MPa), and ductility (from 55.4% to 56.1%). It is shown that these comprehensive enhancements of strength and ductility result from the effect of interstitial solid solution strengthening by carbon alloying and second phase strengthening via the eutectic structure.