Developing a new type of directly casting AlxCr6.85Fe28Ni65.15-x eutectic or near-eutectic high-entropy alloys with a favorable strength-ductility synergy

Abstract

To address the poor casting performance and compositional inhomogeneity of conventional alloys, the proposal of eutectic high-entropy alloys (EHEAs) shows great promise for extensive practical applications. Here, a series of Al_xCr_6.85Fe₂₈Ni_65.15-x (x = 17, 18, 19 at%) HEAs with FCC/L1₂ and BCC/B2 phases were developed. With the Al content increasing from 17 at% to 19 at%, the microstructure of the studied HEAs undergoes a sequential transformation from hypoeutectic structure to eutectic structure and then to hypereutectic structure. And then, the yield strength (YS) and ultimate tensile strength (UTS) of the studied HEAs exhibit a trend of rising first and then declining, while the total elongation (TE) first decreases and then slightly increases. Among them, the Al₁₈Cr_6.85Fe₂₈Ni_47.15 EHEA shows the best strength-ductility balance, which outperforms most reported EHEAs. Specifically, its YS, UTS and TE are 725 MPa, 1417 MPa and 18.1%, respectively. Such outstanding strength of the EHEA is derived from the synergistic effects of the precipitation strengthening, friction stress strengthening and grain boundary strengthening. The L1₂ and B2 nanoprecipitates make the most significant contribution to the strengthening of the Al-18 EHEA. This design strategy paves a novel path for the development of high-performance alloys.