Synthesis of a novel functionally graded coatings of Ni-Cr/Al2O3 nanocomposite coating by pulse electrodeposition

Ni-Cr/Al2O3 nanocomposite coating with functionally graded (FG) structure was deposited by successive changing of pulse duty cycle. The pulse duty cycle altered from 45% to 80% in 7 steps. The content of Cr was increased from 3 wt% for the first layer to 78% for the top layer. Also, the distribution of nanoparticles across the coating had a gradual form as the highest content of nanoparticles was entrapped in the top layer. This type of deposition induced a gradual variation of properties as the hardness increased across the coating towards the top surface. This behavior improved the wear resistance so that the wear rate decreased 39% comparing with monolayer coatings. The corrosion study of coating showed a 99.7% decrease in corrosion current density for FG nanocomposite that is attributed to the layered structure of coating and high content of Cr and nanoparticles on the outer surface.