Effects of the anion in glycine-containing electrolytes on the mechanical properties of electrodeposited Co–Ni films

Tailoring of the mechanical properties (e.g., hardness, Young's modulus or wear characteristics) of Co–Ni electrodeposits has been accomplished by changing the anion (sulphate versus chloride ions) in glycine-containing solutions at 80 °C, while maintaining all the other electroplating conditions unaltered. Galvanostatic deposition on metalized silicon substrates at 5–40 mA cm−2 produced well adherent Co–Ni films with varying surface finish, chemical composition (50–83 wt% Co), morphology and structure. The deposition from chloride salts yielded matte grey, cobalt-rich Co–Ni films with hexagonal close-packed structure and crystallite sizes around 65–85 nm. Films obtained under the same electrodeposition conditions from sulphate salts were Ni-rich, displayed smoother surfaces and smaller crystallite sizes (30–40 nm) belonging mainly to the face-centered cubic phase. The crystallite size played a key role on the mechanical properties of the films, while the composition and the phase percentage had little effect. It is thus demonstrated that the nature of the anion induces a large tunability both in the microstructure and mechanical properties of the deposits. In particular, the nanoindentation hardness could be varied between 1.6 and 7.1 GPa, while the Young's modulus ranged between 122 and 181 GPa.

► Co–Ni films with varying microstructure and mechanical behavior were electroplated.
► Tailoring was achieved by changing the anion type in glycine-containing solutions.
► Chlorides/sulphates led to Co-rich films (hcp)/Ni-rich films (fcc), respectively.
► Crystallite size, rather than composition, determined the mechanical properties.
► Hardness values as high as 7.1 GPa were achieved for ∼50:50 Co/Ni weight ratios.