Effect of Pulse Current and Duty cycle on Nanostructure of Ni-Co coating by pulse electroplating

In this research Ni-Co coating is deposited by square wave and then the influence of pulse current and duty cycle on Co content and hardness of Ni-Co alloy coatings are respectively investigated by SEM and EDX. The results show that Co content of Ni-Co alloy coating increases when the current density decreases. When currentdensity is small, the coating crystalline grains size is tiny and the crystalline grains arrangement is relativelyclose. In the Ni-Co electrodepositing process, the combining of Ni2+ and Co2+ generates [CoNi (II)] intermediate products, then the decomposion of [CoNi (II)] generates Co2+ and Ni2+.This prevents the sedimentation of Ni2+ ions and increases the sedimentary speed of Co2+ ions. With the decrease of duty cycle in Ni-Co coating, anincrease in hardness of coating was observed which resulted in the grain refinement and then a decrease inhardness due mainly to reduction of cobalt content of coating was observed. the root cause of this phenomenon 2is that Ton is shorter and Co2+ ions have less opportunity for deposition. In addition with the increase in duty cycle, Ton and deposition rate increase and it causes an increase in the thickness of coating.

کلیدواژه ها:

Pulse electroplating ، Ni-Co coating ، Nanostructure ، Duty cycle ، Pulse current