Microstructure and Mechanical Properties of As-Cast and Laser Powder Bed Fused AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

Eutectic high-entropy alloys (EHEAs), as a typical kind of in situ composite, have become a potential alternative for conventional alloys because of their advantages in high-entropy alloys and eutectic alloys. Casting is the conventional preparation method of EHEAs, which is a well-established process with low production efficiency. Laser powder bed fusion (LPBF) is an economical and effective preparation technology that provides a novel way to directly form fine and complex EHEA components. In this study, considering the different application requirements and technical characteristics, AlCoCrFeNi2.1 EHEA was prepared by vacuum induction melting and LPBF, respectively. The effect of the preparation process on the microstructure of the alloy was investigated. In addition, tensile properties of the samples at 20, 500, and 700 degrees C were investigated. Results showed that as-cast and LPBF-formed AlCoCrFeNi2.1 exhibited a eutectic structure composed of alternating fcc and bcc/B2 phases. The high heating and cooling rates during the LPBF process were conducive to the formation of ultrafine and uniform eutectic lamellae, which significantly reduced element segregation. During tensile deformation at room temperature, considering the strong phase boundary strengthening and dual-phase synergistic deformation, the ultimate tensile strength of the LPBF-formed sample was enhanced by about 28% compared with that of the as-cast sample, and a satisfactory elongation of 10% was obtained. At 500 degrees C, the mechanical properties of the as- cast and LPBF-formed samples decreased probably because of the severe phase transformation in the alloy. When the testing temperature was increased to 700 degrees C, the mechanical properties of the as-cast sample continued to decrease. The LPBF-formed samples showed a low tensile strength and superior elongation that should be attributed to the eutectic lamellae sliding along the phase boundaries at high temperatures. Meanwhile, the fracture mechanism of the LPBF-formed sample was dominated by ductile fracture. This work could provide a theoretical basis for the optimization of the microstructure and mechanical properties of EHEAs, thereby promoting their industrial application.