A comparison between fine-grained and nanocrystalline electrodeposited Cu–Ni films. Insights on mechanical and corrosion performance

Abstract

Cu 1 − x –Ni x (0.43 ≤ x ≤ 1.0) films were electrodeposited from citrate–sulphate baths at different current densities onto Cu/Ti/Si (100) substrates with the addition of saccharine as a grain-refining agent. The Cu–Ni alloy films produced from saccharine-free baths were fine-grained (crystallite size of ~ 400 nm). The addition of saccharine to the electrolytic solution induced a dramatic decrease in crystal size (down to ~ 27 nm) along with a reduction in surface roughness. Although the effect of saccharine on pure Ni films was less obvious, significant changes were observed due to the presence of saccharine in the bath during the alloying of Cu with Ni. Compared to fine-grained Cu–Ni films, the nanocrystalline films exhibited lower microstrains and a larger amount of stacking faults as observed by X-ray diffraction. These features enhance the mechanical properties of the Cu–Ni alloys, making the nanocrystalline Cu–Ni films superior to both the corresponding fine-grained films and pure Ni films. In particular, hardness in fine-grained films varied from 4.2 ( x = 0.43) to 5.4 GPa ( x = 0.86), whereas hardness varied between 6.7 and 8.2 GPa for nanocrystalline films of similar composition. In addition, wear resistance and elastic recovery were enhanced. Nanostructuring did not significantly affect corrosion resistance of Cu–Ni alloys in chloride media. Although the corrosion potential shifted slightly towards more negative values, the corrosion current density decreased, thereby making the electrodeposition nanostructuring process an effective tool to improve the overall properties of the Cu–Ni system.