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), AlCoCrFeNi2.1 can achieve the fair matching of strength and ductility, which has attracted wide attention. However, the engineering applications of as-cast AlCoCrFeNi2.1 EHEAs 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 AlCoCrFeNi2.1 EHEA 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 AlCoCrFeNi2.1 EHEA 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 similar to 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. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.

Automated summary

In this study, the selective laser melting (SLM) technique was used to prepare AlCoCrFeNi2.1 EHEA, achieving a good balance between strength and ductility. The SLM-ed samples exhibited a complete eutectic microstructure consisting of ultra-fine FCC and ordered B2 phases. The eutectic morphology transformed from lamellar structure to cellular structure as the laser energy input decreased. The SLM-ed AlCoCrFeNi2.1 EHEA demonstrated excellent mechanical properties, including high tensile strength, yield strength, and good ductility, which can be attributed to the ultra-fine grains and heterogeneous structure.