J. Mater. Sci. Technol. ›› 2016, Vol. 32 ›› Issue (3): 245-250.DOI: 10.1016/j.jmst.2015.08.006

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Microstructure and Mechanical Properties of a CoFeNi2V0.5Nb0.75 Eutectic High Entropy Alloy in As-cast and Heat-treated Conditions

Li Jiang1, Yiping Lu1, 2, Wei Wu1, Zhiqiang Cao1, Tingju Li1   

  1. 1 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China;
    2 State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
  • Online:2016-03-10
  • Contact: Assoc. Prof., Ph.D.; Tel.: +86 411 84709400; Fax: +86 41184708940.
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (Nos. 51104029, 51134013, 51471044, 51104029 and 51375070), the Fundamental Research Funds for the Central Universities, and the Natural Science Foundation of Liaoning Province (No. 2014028013).

Abstract: The eutectic CoFeNi2V0.5Nb0.75 high entropy alloys (HEAs) were heated at 500, 600, 700, 800 and 1000 °C, 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 CoFeNi2V0.5Nb0.75 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 °C. 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 °C 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 CoFeNi2V0.5Nb0.75 HEAs exhibited apparent age hardening, especially quenched at 700 °C, the hardness reached up to the maximum value of HV 727.52.

Key words: High entropy alloy, Microstructure, Thermal stability, Age hardening