Microstructural, Mechanical, And Corrosion Behaviour of Ni–Fe‑Cr‑Al and Ni–Fe‑Cr‑Al‑Co Alloys

High entropy alloys (HEAs) with excellent strength-ductility combinations are considered potential candidates for various structural and aerospace applications. Despite its promising mechanical properties, there have been contradictory observations related to the corrosion behaviour of HEAs. Therefore, the present study aimed to design low-density cost-effective medium entropy alloys exhibiting the popular γ-γʹ microstructures of super alloys and to evaluate their mechanical properties and corrosion behaviour. The CALPHAD-based approach was used to design two alloy systems, Ni–Fe-Cr-Al (0Co) and Ni–Fe-Cr-Al-Co (14Co). These alloys were produced through induction melting and casting route. The microstructure and room-temperature mechanical properties of the alloys were thoroughly investigated employing various characterization tools. Further, the corrosion behaviour of the developed alloys was investigated through electrochemical and gravimetric techniques, followed by surface topography studies. Both the alloys exhibited excellent strength-ductility synergy and the addition of Co significantly improved the mechanical properties. It is interesting to note that 0Co alloy exhibited better corrosion resistance compared to 14Co alloy in an electrochemical test using 3.5wt.% NaCl solution. Moreover, no significant influence of Co could be confirmed during the immersion test in 6wt.% FeCl3 solution. Further, the potentiodynamic results obtained for both the studied alloys exhibited corrosion rates comparable to SS304 as well as other studied HEAs while possessing better room-temperature mechanical properties.