Sediment Co-Deposition of Nanostructured Ni-Al2O3 Composite Coatings

Nanostructured Ni-Al2O3 composite coatings incorporated with various contents of α-Al2O3 nano-particles were prepared on mild steel by using novel sediment co-deposition (SCD) technique. For the comparison reason, the pure Nickel coating and the Ni-Al2O3 composite coatings were fabricated by means of conventional electroplating (CEP) technique. The electroplating was carried out in Watt’s bath without any additives except for nano-α-Al2O3 suspension. The influence of the nano-particulates concentration, current density, and the mode of electroplating on the composite coatings were investigated. The results reveal that the weight percent of nano-Al2O3 increases with increasing nano-α-Al2O3 concentration in plating bath and some agglomeration occurs on the surface of composite coatings. The current density affects the alumina content in the composite coatings as well. The nano-α-Al2O3 incorporation by the SCD technique is higher than that of the CEP technique. The microhardness increases, while the wear rate decreases with increasing content of the nano-Al2O3 in the composite coatings. The incorporation of nano-α-Al2O3 particles changes the surface morphology of Ni matrix and modifies the texture of composite coating to exhibit a preferentially (111) growth orientation. Moreover, the co-deposited nano-sized α-Al2O3 particles are uniformly distributed in the Ni matrix and contributed to remarkably increase the microhardness, and tribological properties of the Ni base coating.