Design and development of CoCrFeNiTa eutectic high entropy alloys

Abstract

High entropy alloys (HEA) are an emerging class of metallic materials that have shown the potential to outsmart conventional alloy systems in terms of different physical and mechanical properties. Development of eutectic microstructure in high entropy alloys can help in obtaining even better combination of mechanical properties due to fine distribution of phases. Eutectic high entropy alloys have been developed in the present study by addition of tantalum to the CoCrFeNi system. Pseudo binary phase diagram of CoCrFeNi–Ta was calculated with the help of Thermocalc software. Different alloy compositions were prepared by arc melting under argon atmosphere. Development of lamellar microstructure consisting of FCC and Laves phase was confirmed by the microstructural and crystal structure characterization carried out with the help of SEM and XRD. Necessary changes in the calculated phase diagram, in the light of microstructure and crystal structure characterization results, has been proposed. To evaluate the effect of eutectic microstructure on the mechanical properties of developed alloys, mechanical characterization was carried out with the help of compression tests and hardness tests. Development of eutectic microstructure consisting of FCC and Laves has helped in significantly improving the yield strength of developed alloys without causing drastic decrease in ductility. Completely eutectic alloys have shown better combination of mechanical properties in comparison to the respective hypoeutectic and hypereutectic high entropy alloys. It is believed that development of complete eutectic microstructure in high entropy alloys can help in obtaining alloys with significantly improved combination of strength and ductility.