Strategies to engineer FeCoNiCuZn high entropy alloy composition through aqueous electrochemical deposition

Low melting point elements are often incompatible with alloy synthesis methods that involve high temperatures, and thus, high entropy alloys containing zinc (Zn) have not been explored much to date, hindering the development of new alloy system investigations. In such cases, electrodeposition can be a useful alternative for the synthesis of multi-component (MCA)/high entropy alloys (HEA) which contain elements with large differences in their melting point and those that cannot be easily synthesized through established conventional/melting-casting routes. Though electrodeposition is an age-old technique, exploration of this synthesis route for fabricating HEAs is recently gaining attention, and more specifically, aqueous medium electrodeposition is still in its infancy. The current work reports a HEA containing Zn, namely, FeCoNiCuZn, through electrodeposition in an aqueous medium utilizing sulfate salts. Electrodeposition was carried out by varying different input parameters, namely, duty cycles (input pulse parameters), pH, and substrate roughness. Through these different input parameters, their effects on the composition, phase, and morphology of the deposited films are a matter of investigation. Observations revealed that the composition of the electrodeposited FeCoNiCuZn thin film is highly dependent on the input pulse parameters and the pH, whereas the substrate roughness played no observable significant role, probably owing to the use of pulsed waveform and the very low film thickness (∼ 500 nm). The compositional characterization of the electrodeposited FeCoNiCuZn showed the presence of a high percentage of Cu (> 50 at.%) at lower duty cycles (< 0.75), whereas higher duty cycle (> 0.75) resulted in FeCoNiCuZn HEAs with all five elements in almost equal proportion. Alternatively, lower pH (≤ 1.5) led to high Cu content in the thin film, whereas higher pH (≥ 2.5) resulted in a multi-elemental deposition.