Mechanical Properties and Corrosion Behaviour of Nanostructured Cu-rich CuNi Electrodeposited Films

Abstract

Nanocrystalline Cu-rich CuNi alloy thin films (with copper content ranging from 22 to 97 at%) have been grown by electrodeposition, using galvanostatic conditions in an electrolytic bath containing Ni and Cu sulphates with a [Ni(II)]/[Cu(II)] molar ratio of 11. The Cu content is tuned by varying the applied current density during deposition. The nanoscrystalline nature of Cu-rich CuNi thin films has been achieved using saccharine as a grain refinement agent, although for high Cu content (> 90 at%) the refinement effect is less pronounced. Due to the nanocrystalline character of the films, low surface roughness, good compactness, and outstanding mechanical properties (e.g. nanoindentation hardness values off approximately 7 GPa) are obtained, particularly for Cu percentages below 70 at%. The presence of stacking faults also contributes to the observed high strength. The films show good corrosion protective behaviour in a 3.5 wt% NaCl medium, with corrosion potentials more positive than the bare substrate (pure-Cu) and lower corrosion current density values ranging from 1.8 to 5.4 [mi]A/square centimeters