Microstructure and Mechanical Properties of As-Cast and Laser Powder Bed Fused AlCoCrFeNi2.1 Eutectic High-Entropy Alloy
TANG Xu1,2, ZHANG Hao1(), XUE Peng1, WU Lihui1, LIU Fengchao1, ZHU Zhengwang1, NI Dingrui1(), XIAO Bolv1, MA Zongyi1
1 Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
TANG Xu, ZHANG Hao, XUE Peng, WU Lihui, LIU Fengchao, ZHU Zhengwang, NI Dingrui, XIAO Bolv, MA Zongyi. Microstructure and Mechanical Properties of As-Cast and Laser Powder Bed Fused AlCoCrFeNi2.1 Eutectic High-Entropy Alloy. Acta Metall Sin, 2024, 60(11): 1461-1470.
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°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°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°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.
Fund: National Natural Science Foundation of China(U21A2043);Youth Innovation Promotion Association, CAS(2022191);Bintech-IMR Research and Development Program(GYY-JSBU-2022-010)
Corresponding Authors:
NI Dingrui, professor, Tel: (024)23971752, E-mail: drni@imr.ac.cn;
Fig.1 SEM image (a) and size distribution (b) of the AlCoCrFeNi2.1 powders
Fig.2 Schematic illustration of the tensile specimens (unit: mm)
Fig.3 OM images of microstructures of as-cast sample (a), Y-Z plane (b), and X-Y plane (c) of laser powder bed fusion (LPBF)-formed AlCoCrFeNi2.1 sample (X—horizontal direction, Y—scanning direction, Z—construction direction)
Fig.4 XRD spectra of as-cast and LPBF-formed AlCoCrFeNi2.1 samples
Fig.5 SEM images of as-cast sample (a), Y-Z plane (b), and X-Y plane (c) of LPBF-formed sample
Fig.6 STEM dark field images, selected area electron diffraction patterns, and EDS maps of as-cast (a) and LPBF-formed (b) AlCoCrFeNi2.1 samples
Fig.7 Tensile stress-strain curves of as-cast (a) and LPBF-formed (b) AlCoCrFeNi2.1 samples at different temperatures, and variations of ultimate tensile strength (c) and elongation (d) with temperature
Fig.8 Phase diagram of AlCoCrFeNi2.1 alloy (Thermo-Calc)
Fig.9 SEM images of fracture surfaces of as-cast (a-c) and LPBF-formed (d-f) AlCoCrFeNi2.1 samples after tensile fracture at 20℃ (a, d), 500℃ (b, e), and 700℃ (c, f)
Fig.10 SEM images of fracture longtudinal sections of as-cast (a, c, e) and LPBF-formed (b, d, f) AlCoCrFeNi2.1 samples after tensile fracture at 20oC (a, b), 500oC (c, d), and 700oC (e, f)
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