Study on corrosion behavior of Ni–P/Ni–Cu–P superhydrophobic composite coatings preparation on L360 steel by two-step method

The two-step process of electroless plating and electrodeposition was used to successfully prepare a bilayer composite film by electroplating a Ni–Cu–P film with hydrophobic properties on the Ni–P film. The histological features of the two membrane layers were compared. The L360 pipeline steel, Ni–P coating and Ni–Cu–P composite film were evaluated by electrochemical test and erosion corrosion method. Under simulated seawater conditions, the material properties changed before and after different periods of service. The experimental results show that the introduction of Cu can inhibit the growth of cellular structures on the surface of the coating, increase the number of nucleation points, and improve the microstructure of the coating during the deposition of Ni–Cu–P films. The Ni–P/Ni–Cu–P bilayer composite film has a pinecone-like convex structure, which can greatly reduce the surface energy of the film layer and endow the film layer with hydrophobicity. At the same time, it effectively resists the adsorption of water and other external impurities on its surface, and has good anti-fouling performance, thereby slowing down the surface corrosion and improving corrosion resistance. In addition, copper enables the composite coating to have passivation and a uniform and dense coating structure, which is the main reason for the improvement of the corrosion protection performance of the composite coating. The protective effect of the coating can effectively improve the electrochemical resistance and erosion resistance of L360. The Ni–P/Ni–Cu–P bilayer composite film reduces the electrochemical corrosion rate of the substrate from 0.417mmpY to 0.025mmpY, and the scouring weight loss rate of the film decreases to 0.05% of the substrate.