Comparing the corrosion resistance of Cu–Ni alloys and electroless Ni-B and Ni-P coatings in seawater

Given the widespread use of cupronickel alloys in the marine industry, despite their higher cost than pure copper, this work explores the application of Ni-B and Ni-P coatings on pure copper as a potential alternative. Ni-6 wt-% B (Ni-B) and Ni-11 wt-% P (Ni-P) coatings were applied to a pure copper substrate using an electroless process. The microstructure and morphology of the coatings were analysed using X-ray diffraction and field emission scanning electron microscopy. The corrosion behaviour of the coatings, along with Cu–10 wt-% Ni (Cu–10Ni), Cu-20 wt-% Ni (Cu–20Ni), and pure copper, was investigated in simulated seawater using electrochemical impedance spectroscopy and potentiodynamic polarisation methods. The results showed that the Ni-P coating exhibited the highest corrosion resistance (4.5 × 10 −7 A·cm −2 ), followed by the Ni-B coating (5.5 × 10 −7 A·cm −2 ). The corrosion resistance of Cu–10Ni (1.2 × 10 −6 A·cm −2 ) and Cu–20Ni (1.1 × 10 −6 A·cm −2 ) was superior to that of pure copper (2.5 × 10 −6 A·cm −2 ). The corrosion mechanism of the alloys is influenced by both the charge transfer process and diffusion. Significant higher hardness of the Ni-B (930 ± 10 HV 100 ) and Ni-P (605 ± 5 HV 100 ) coatings compared to the bare alloys suggests improved tribological performance.