Compositional modulation through galvanic displacement in electrochemically deposited FeCoNiCuZn high entropy alloy thin films

After completing the aqueous electrodeposition of FeCoNiCuZn nanocrystalline high entropy (HEA) alloy system consisting of elements with significant differences in melting points and reduction potentials, unwanted galvanic displacement reactions (GDR) were observed on the alloy system when the film was held back in the electrolyte. This phenomenon, observed in alloys electroplated from aqueous baths containing a noble metal (currently Cu), leads to preferential deposition of the noble elements and changes the composition progressively at open circuit potential. A change in composition occurs in the electrodeposited alloy where Cu (from similar to 13 to 58 at. %) was deposited on the alloy due to its nobler reduction potential causing displacement of Zn > Fe similar to Co > Ni (order of displacement) from the deposited alloy with the Cu2+ ions present in the electrolyte. This work is the first observational report of galvanic displacement in HEAs composed of five elements. We categorically state that this GDR is crucial when designing/synthesizing HEAs alloys through electrodeposition.

Automated summary

After electrodeposition, galvanic displacement reactions were observed on the FeCoNiCuZn nanocrystalline HEA alloy system, which consisted of elements with significant differences in melting points and reduction potentials, when the film was held back in the electrolyte. This phenomenon leads to preferential deposition of the noble elements and gradual change in composition at open circuit potential. The deposition of Cu from the electrolyte caused displacement of Zn > Fe similar to Co > Ni from the electrodeposited alloy. This is the first observational report of galvanic displacement in HEAs composed of five elements.