Effect of electroless Ni plating on the properties of cold-sprayed Ni-Al2O3 coatings

This study investigated the effect of electroless nickel (Ni) plating (N-p) on the properties of cold-sprayed nickel-alumina (Al2O3) coatings. To develop this two-layered coating system, nickel-alumina powder coating was first deposited by the cold spraying method on a mild steel substrate. Then, electroless Np was deposited on the as-sprayed nickel-alumina coating. The coating properties of the as-sprayed nickel-alumina coating and of the two-layered Np/nickel-alumina system were critically examined. The microstructural evolution was analysed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In order to study possible changes in the mechanical properties of the system, Vickers microhardness experiments on the coatings and on the cross-sections were conducted. A possible improvement in the microhardness (14%) of the system was found after Np. Further, the corrosion behavior of the coating system was also studied critically. It was observed that the corrosion resistance of the Np/nickel-alumina coating system significantly improved and no corrosion effects and crack generation were observed at the substrate-coating interface.