Development of CoCrFeNi based EHEAs by Individual Addition of Mo, Ta and W

Abstract

Single FCC solid solutions are known to exhibits greater ductility but relatively poor strength. On the other hand single BCC solid solution and intermetallic provide good strength but poor ductility. A mixture of both provides a better trade off of the two properties. Conventional alloys pose restriction to this method because of their compositional limitation. Recently study on the High Entropy Alloys (HEAs) has shown to overcome this limitation. In order to achieve even better of the two properties, Eutectic HEAs (EHEAs) were created of the three systems mentioned above using vacuum arc furnace. In this study, three systems of CoCrFeNiTax, (CoCrFeNiWx and CoCrFeNiMox (x value in molar ratio, x=0.1, 0.25, 0.5, 0.75, and 1) high entropy alloys were prepared to study the effect of Ta, Mo and W addition on the microstructure and mechanical properties. Microstructure was studied through SEM and optical microscope while phase identification through XRD characterization. Compression and hardness test where further carried out to evaluate mechanical properties. Ultrafine lamellar eutectic microstructure (CoCrFeNiTa0.75) proved to be able to achieve very high yield strength. In CoCrFeNiTax system microstructure started from FCC, progressed through hypoeutectic x=0.25 and 0.5, achieved eutectic composition at x=0.75 and finally entered hypereutectic region at x=1. In case of CoCrFeNiWx FCC phase remained dominant for x=0.1, 0.25 and showed an increase of eutectic region with increase in x=0.5, 0.75 and 1. Finally CoCrFeNiMox showed eutectic microstructure at x=1 which exhibited high strength and ductility.