Microstructure and Mechanical Properties of a CoFeNi₂V_0.5Nb_0.75 Eutectic High Entropy Alloy in As-cast and Heat-treated Conditions

Li Jiang¹，Yiping Lu^1,2，Wei Wu¹，Zhiqiang Cao¹，Tingju Li¹

1. School of Materials Science and Engineering, Dalian University of Technology2. State Key Laboratory of Metastable Materials Science and Technology, Yanshan University

摘 要：The eutectic CoFeNi₂V_0.5Nb_0.75 high entropy alloys（HEAs） were heated at 500, 600, 700, 800 and 1000 ℃,respectively for 6 h and subsequently quenched in the water to investigate their thermal stability and phase transformation at high temperature. The microstructure and mechanical properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, compressive and hardness tests. It was found that the as-cast CoFeNi₂V_0.5Nb_0.75 HEAs showed a eutectic microstructure with alternating fcc solid solution phase and Fe₂Nb-type Laves phase. The NbNi₄-type intermetallic phase appeared when the heat-treated temperature was higher than 600 ℃. With increasing quenching temperature, the volume fraction of the NbNi₄-type intermetallic phase increased while that of the eutectic regions decreased.The sample quenched at 800 ℃ showed the most excellent comprehensive mechanical properties; its fracture strength, yield strength and plastic strain were as high as 2586.76 MPa, 2075.18 MPa and 16.73%,respectively. Moreover, the eutectic CoFeNi₂V_0.5Nb_0.75 HEAs exhibited apparent age hardening, especially quenched at 700 ℃, the hardness reached up to the maximum value of HV 727.52.

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