Deposition of Nickel-tungsten-phosphorus Coatings on Pure Copper in a Saline Water Environment

Corrosion of copper caused by chloride species restricts advances in the maritime industry. In the present study, ternary Ni-W-P alloys were electrodeposited on copper in DC current mode to improve the corrosion resistance of the matrix. Then, a SEM equipped with EDAX was employed to investigate the surface morphology and texture of the coating layer. These coatings demonstrated dense microstructures with nodular shapes and few defects in morphology. Potentiostatic polarization and open-circuit tests were employed to investigate the corrosion resistance of the copper matrix with and without coating in 3.5 wt% NaCl. Additionally, a high phosphorus content (ranging from 11-14 wt%) enhanced the corrosion resistance of the coated copper matrix. The corrosion currents (I-corr) of the copper without and with coating were 5.72E(-5) A/cm(2) and 7.01E(-7) A/cm(2), respectively. In the open-circuit test, the corrosive rate decreased when the passive film existed on the surface, while the ternary Ni-W-P coating was exposed to saline water. A slow-strain-rate test (SSRT) was performed in the atmosphere and saline water to evaluate the mechanical properties of the specimens. The strengths of the copper matrix with and without coating were 310 MPa and 240 MPa, respectively. The ternary Ni-W-P coating effectively increased the ultimate tensile strength (UTS) of the substrate during the slow-strain-rate test (SSRT). Furthermore, the specimen seriously deteriorated in the saline water, and it was accompanied by partial brittle fracture due to stress cracking on the adjacent failure surface.