Fabrication of functionally gradient nanocomposite coatings by plasma electrolytic oxidation based on variable duty cycle

► Si3N4 content in the layer increases with the increase of its concentration in bath. ► Microhardness of layers increases with weight percentage of nanoparticulates. ► Coatings fabricated with lower rate of variable duty cycle has higher microhardness. ► Microhardness profile of the coatings showed different zones.