Abstract
Face centered cubic (FCC) high-entropy alloys (HEA) exhibit excellent ductility while body centered cubic (BCC) HEAs are characterized by high strength. Development of fine two-phase eutectic microstructure (consisting of a tough phase such as fcc and a hard phase such as bcc/intermetallic) can help in obtaining an extraordinary combination of strength and ductility in HEAs. Designing eutectic high entropy alloys is an extremely difficult task for which different empirical and non-empirical methods have been previously tried. In the present study, the possibility of developing a eutectic microstructure by the addition of Mo to CoCrFeNi was evaluated by calculation of the pseudo-binary phase diagram. Experimental results validated the presence of eutectic reaction in the calculated phase diagrams; however, small changes in the calculated phase diagrams were proposed. It has been shown that calculated pseudo-binary phase diagrams can provide a very good starting point for the development of eutectic HEAs and help in exponentially reducing the amount of experimental effort that may be required otherwise. Eutectic mixture consisting of FCC (A2) phase and intermetallic phases (σ and μ) was successfully obtained by the addition of Mo to the CoCrFeNi system. The development of the eutectic microstructure showed a profound effect on the mechanical properties. Hardness of the samples increased from 150 HV for CoCrFeNiMo0.1 to 425.5 HV for CoCrFeNiMo1.0, whereas yield strength increased from around 218 MPa for CoCrFeNiMo0.1 to around 1100 MPa for CoCrFeNiMo1.0.
Highlights
Conventional alloys are currently used for the majority of structural applications
The present study was aimed at the development of a eutectic high-entropy alloys (HEA) consisting of finely distributed fcc and intermetallic phases in order to obtain an extraordinary combination of strength and ductility
A pseudo-binary phase diagram of the CoCrFeNi-Mo system was successfully calculated with the help of the Thermo-Calc software package using the TCHEA database
Summary
Conventional alloys are currently used for the majority of structural applications. Some of the common examples include the use of aluminum alloys and titanium alloys for applications requiring high strength/weight ratios (aerospace industry) [1], steels as a loadbearing material for applications requiring high strength and ductility at low cost [2,3,4,5,6,7], cobalt-based alloys for biomedical applications [8,9,10], and nickel-based superalloys for applications requiring high resistance to mechanical degradation at elevated temperatures [11,12]. Some of the outstanding mechanical properties of high-entropy alloys include high wear resistance [25,26], high strength even at high temperatures [18,27,28], tremendous thermal stability [27,28,29], and good corrosion resistance [30,31,32,33]. The first eutectic high-entropy alloy (AlCoCrFeNi2.1) consisting of a ductile FCC and hard BCC phase was designed and synthesized [47] in 2014 and exhibited an excellent combination of ductility and strength. The present study was aimed at the development of a eutectic HEA consisting of finely distributed fcc and intermetallic phases in order to obtain an extraordinary combination of strength and ductility. Eutectic HEAs consisting of FCC and intermetallic phases have been successfully developed, and the effect of the developed eutectic mixture on the mechanical properties of the studied alloys has been evaluated
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