Electrodeposition of silver-carbon coatings with low contact resistance and wear rate

Composite coatings of silver with self lubricating carbon nano particles were made by electrocodeposition. Ultrasonic disintegration during deposition was used to prevent coagulation of particles in the electrolyte in order to obtain a high and uniform particle incorporation. The effect of current density, particle concentration and rotation speed on particle incorporation was studied. Depending on the deposition parameters, a particle incorporation of 14 vol% could be obtained. The contact resistance of the coatings was measured during reciprocating fretting in order to study their behavior for electrical connector applications. It was found that there was a threshold value of 9 vol% carbon black particles in the coating above which the friction coefficient, the wear rate and the electrical properties drastically change. When there is less than 9 vol% of carbon black, the friction coefficient equals the friction coefficient of pure silver, the wear rate is large and the contact resistance shows spikes above 100 Ω during fretting. With more than 9 vol% of carbon black, a friction coefficient of 0.2 is obtained which is 4 times smaller than below the threshold value, the wear rate is lowered by a factor 14 and the contact resistance during fretting is below 1 mΩ without spikes.