Nanocrystalline metals and alloys with grain sizes smaller than 100 nm have attracted
extensive interest due to their improved mechanical, physical and chemical properties.
Although electrodeposition has been one of the methods for synthesizing nanocrystalline
materials, properties of nanocrystalline electrodeposits are less evaluated, especially for
tribological applications or potential applications in nanoscale devices such as
MEMS and NEMS. In this work, nanocrystalline and microcrystalline copper
deposits were produced by pulse and direct current electrodeposition processes
respectively. Effects of deposition parameters, such as the peak density, frequency,
current-on time and current-off time of the pulse current (PC), on the grain size were
investigated for the purpose of process optimization. The grain size of nanocrystalline
coatings was determined using x-ray diffraction and atomic force microscopy (AFM).
Mechanical and tribological properties of the deposits were investigated using
nanoindentation, nanoscratch and microscratch techniques. It was demonstrated that the
nanocrystalline film was markedly superior to regularly grained film made by direct current
(DC) plating; the nanocrystalline deposit shows higher hardness, lower friction
coefficient and lower wear rate. The surface electron stability and chemical reactivity
of the deposits were also evaluated by measuring their electron work function
(EWF). Results indicate that the nanocrystalline surface is more electrochemically
stable than the DC-plated one. This increased stability result is attributed to the
formation of a stronger and more adherent passive film on the nanocrystalline
copper, confirmed by potentiodynamic polarization and electrical contact resistance
measurements.