A new blackening process for NiWP alloy deposits

Black coatings have been widely used in industries for their excellent decorative, physical and mechanical properties. In this paper, a new blackening process of the NiWP deposits was reported. Uniform black coatings can been obtained by simply immersing the NiWP deposits with less than 26.35% (by weight) of W content in the HCl–H2O2–HF solution. The influence of tungsten content on blacking was discussed by comparing morphology and chemical composition of the NiWP deposits. The formation mechanism studies of black film showed that the black color of the NiWP deposit was caused by both its unique dense meshwork morphology at the surface of the NiWP black layer as well to the formation of oxides (NiO, Ni2O3 and WO3) and phosphate products (Ni(H2PO4)2). Optical property, thermal stability and corrosion resistance of the black ternary NiWP coatings were also studied in detail.