High Phosphorus Nickel Alloy Deposition by Brush Plating Process

Nickel (Ni) alloy coating with high phosphorus (P), P > 10wt.%, is usually deposited by electroless and electrolytic plating processes and has been widely used for corrosion and wear resistance applications. However, the deposition rate is low and plating tanks with temperature control are required, and not viable for on-site coating and coating repair. The tank-free brush plating is usually controlled by constant voltage and featured with high deposition rate due to high current density (>100 A/dm²), while the current density of conventional tank plating is usually lower than 10 A/dm². However, the high current density of brush plating leads to a challenge to deposit a high phosphorus (Hi-P) Ni alloy, as the P content in the nickel phosphorus (NiP) alloy coating is inversely proportional to the operating current density based on the tank plating practices. In this paper, we report a brush plating process to deposit high phosphorous nickel thin film on carbon steel coupons. Design of experiments (DOE) was used to optimize the brush plating process, including plating bath formation, and plating parameters. It is found that low pH value and high phosphorous acid (H₃PO₃) concentration in the plating bath are beneficial for high P content in the NiP deposit. High pH value and low 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) concentration are beneficial for high current efficiency. By using the optimized bath chemistry and plating parameters, NiP coating with P content of 13.7 wt% was deposited on carbon steel coupons with a current efficiency as high as 19.4%.