A superfine eutectic microstructure and the mechanical properties of CoCrFeNiMo x high-entropy alloys
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ARTICLE A superfine eutectic microstructure and the mechanical properties of CoCrFeNiMox high-entropy alloys Yong Guo, Liang Liu,a) Yue Zhang, Jingang Qi, Bing Wang, Zuofu Zhao, Jian Shang, and Jun Xiang Department of Materials Science and Engineering, Liaoning University of Technology, Jinzhou Liaoning 121001, China (Received 1 March 2018; accepted 14 May 2018)
A series of CoCrFeNiMox (x 5 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) high-entropy alloys were designed to develop a eutectic high-entropy alloy system and to acquire a superfine eutectic structure. The results show that for the CoCrFeNiMox alloys, with the increase of Mo content from 0.2 to 1.2, the microstructures shift from a typical dendrite structure to a hypoeutectic microstructure (x 5 0.6), and then to a fully eutectic microstructure (x 5 0.8) with a lamellar spacing only 110 nm, and finally culminate in the hypereutectic structure (x 5 1.0, x 5 1.2). The XRD results show that CoCrFeNiMox alloys have a single FCC phase when x is 0.2 or 0.4. When Mo content is over 0.6, it begins to separate Cr9Mo21Ni20 intermetallic compounds. The hardness of the CoCrFeNiMox alloys is increasing significantly from 172.8 to 763.7 HV with the increase of Mo content. Meanwhile, the fracture strength increased but the ductility decreases. Among these alloys, the CoCrFeNiMo0.6 alloy shows excellent integrated mechanical properties of compressive fracture strength and strain, which are 2051 Mpa and 23%, respectively.
I. INTRODUCTION
High-entropy alloys (HEAs), which lead us to a new stage in the study of material science, have been generated significant interest from the scientific community.1,2 The published literature studies reported that many HEA systems exhibit chemical, physical, mechanical, functional, and other exceptional properties, such as high-temperature oxidation-resistant,3 elevated-temperature strength, good wear resistance,4 low density,5,6 high phase stability against irradiation,7 cryogenic stability, low-temperature fracture resistance,8,9 formation of nanostructures,10,11 high yield and fracture strength,12 special near-zero thermal coefficient of electrical resistivity,13 and so on. These splendid characters prompt the research studies on utilizing HEAs in our daily life. Yet, a certain gap between research and actual industrial process still exists. As it is known that the HEAs can hold either high strength or high ductility. However, the simultaneous achievement of both high strength and ductility still confronts a tough challenge. Moreover, the inferior castability and compositional segregation of HEAs has also been another obstacle for their practical applications. From the traditional metallurgical theory, the eutectic alloys are known to be a good candidate to sweep out these issues because the eutectic solidification structure has the following features: (i) near-equilibrium microstructures, which can keep more stable at the high a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.177 J. Mater. Res., 2018
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