Pulse frequency and duty cycle effects on the electrodeposited Ni–Co reinforced with micro and nano-sized ZnO

Ni–Co/ZnO nano and micro composite coating were prepared by PC electrodeposition methods on the pure copper substrate. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, EDAX mapping and atomic force microscopy were employed for investigating of phase structure, surface morphology, elemental analysis, elemental distribution and surface roughness of coatings, respectively. The effects of pulse frequency and duty cycle on the microhardness of coating were investigated. Microhardness of nanocomposite coating was more than that of the microcomposite coating. There were optimum values for pulse frequency and duty cycle (20 Hz, 40% and 10 Hz, 60% for nanocomposite and microcomposite, respectively). Any detour from those optimum values led the microhardness to reduce. Actually pulse frequency and duty cycle influenced the T_ON (electrical current on time) and T_OFF (electrical current off time) values. Optimum T_ON is required to prepare enough electrical attraction force between the particles (surrounded by cationic cloud) and cathode surface. Optimum T_OFF prepared sufficient conditions for particles which be surrounded by cationic cloud and then reach to the cathode surface (using agitation of electrolyte) and reduce there. ZnO microparticles are so greater than ZnO nanoparticles, so more electrical attraction force (lower pulse frequency and higher duty cycle) is required to make them adhere to the cathode surface and prevent from dislodging them from cathode surface by hydrodynamic forces in the electrolyte. Corrosion and wear behaviors of nanocomposite were better than those of microcomposite.