Unique strength-ductility balance of AlCoCrFeNi2.1 eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting

As a typical dual-phase eutectic high entropy alloy(EHEA), AlCoCrFeNican achieve the fair matching of strength and ductility, which has attracted wide attention. However, the engineering applications of as-cast AlCoCrFeNiEHEAs still face challenges, such as coarse grain and low yield strength resulting from low solidification rate and temperature gradient. In this study, selective laser melting(SLM)was introduced into the preparation of AlCoCrFeNiEHEA to realize unique strength-ductility balance,with emphasis on investigating the effects of processing parameters on its eutectic microstructure and properties. The results show that the SLM-ed samples exhibit a completely eutectic structure consisting of ultra-fine face-centered cubic(FCC) and ordered body-centered cubic(B2) phases, and the duplex microstructure undergoes a morphological evolution from lamellar structure to cellular structure as laser energy input reducing. The SLM-ed AlCoCrFeNiEHEA presents an excellent match of high tensile strength(1271 MPa), yield strength(966 MPa), and good ductility(22.5%) at room temperature, which are significantly enhanced by the ultra-fine grains and heterogeneous structure due to rapid solidification rate and high temperature gradient during SLM. Especially, the yield strength increment of ～50% is realized with no loss in ductility as compared with the as-cast samples with the same composition. On this basis, the precise complex component with excellent mechanical properties is well achieved. This work paves the way for the performance improvement and complex parts preparation of EHEA by microstructural design using laser additive manufacturing.