Abstract
Electrodeposition of nanocrystalline nickel on aluminium alloy AA 6061 substrate was carried out using cathodic square wave pulse with an on-time of 0·1 ms and an off-time of 0·9 ms from a modified Watt’s bath containing saccharin as an additive. The influences of concentration of saccharin, pH of the plating bath and average current density on the surface morphology, crystal orientation, average grain size and lattice strain were investigated. The study confirms that increase in concentration of saccharin in the plating bath as well as increase in the average current density results in a decrease in the average grain size of the deposit. pH appears to have no significant effect on the grain size of the deposit. The crystal orientation progressively changes from a strong (200) fibre structure to a (111) (200) double fibre structure as the concentration of saccharin is increased in the plating bath. It was also observed that as the grain size decreases the lattice strain of the coating increases. The space worthiness of the coating has been evaluated by humidity, thermal cycling, thermovacuum performance tests and measurement of optical properties. The coatings were characterised by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy analysis, microhardness evaluation, adhesion, thermal stability and corrosion resistance tests.
Published Version
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