Novel bilayer ZnNi/NiCoSiC nanocomposite coating with exceptional corrosion and wear properties by pulse electrodeposition

This work reports the development of a novel bilayered ZnNi/NiCoSiC nanocomposite coating on mild steel (MS) by electrodeposition. The top Ni-Co-SiC nanocomposite layer, when deposited directly on MS (monolayer) shows a hardness of 734 HV and a corrosion current density of ∼28μA/cm2 in 3.5 wt% NaCl. However, the lack of adherence of the coating with MS results in poor wear and scratch resistance. Mild steel is anodic to NiCoSiC nanocomposite and any kind of discontinuity in the coating may lead to severe galvanic corrosion. This problem has been successfully overcome with the incorporation of an anodic (with respect to mild steel)Zn12%Ni under-layerin between the electrodeposited NiCoSiC nanocomposite coating and MS, which is adherent to both the materials. This bilayer coating has a hardness of 760 HV and corrosion current density of ∼19μA/cm2 in 3.5 wt% NaCl which are slightly better than that of the monolayer. Further, the bilayer coating assembly exhibits exceptionally low volume loss under wear (∼350 mm3) compared to bare mild steel (∼1700 mm3). This ZnNi/NiCoSiC nanocomposite bilayercoating has the potential to emerge as hard, wear resistant and anti-corrosive coating which is essential in the field of heavy duty machines.