Abstract:C_xCoCr₃Fe₅Ni (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 C_0.2CoCr₃Fe₅Ni 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.

Key words: high entropy alloy; M₂₃C₆ carbide; eutectic structure; mechanical properties; strengthening mechanism