The Influence of Ni Incorporation on the Surface Porosity and Corrosion Resistance of CrBN Coatings on 45 Steel in Seawater

By adjusting NiCr target power, five CrNiBN coatings with different Ni contents were fabricated on 45 steel by magnetron sputtering with the aim of improving corrosion resistance of CrBN coatings in seawater. The structure and morphology of CrNiBN coatings were characterized by X-ray diffraction and scanning electron microscope, while its electrochemical properties were evaluated by open circuit potential, electrochemical impedance spectroscopy, and potential dynamic polarization. The results demonstrated that Ni incorporation could reduce the surface porosity of CrBN coatings from 16.8% to 7.7% as Ni content increased from 4.35 at% to 19.62 at%. On this basis, when Ni increased from 4.35 at% to 7.28 at%, self-corrosion potential gradually increased, which prompted the CrNiBN coating with 7.28 at% Ni to present the highest charge transfer resistance Rct of 1.965 × 104 Ω·cm2 and the highest polarization resistance Rp of 74.9 kΩ·cm2. However, more Ni doping from 12.54 at% to 19.62 at% would decrease self-corrosion potential and trigger oxidation. Consequently, the CrNiBN coatings with Ni content from 12.54 at% to 19.62 at% presented decreasing Rct and Rp. Even so, the corrosion resistance of the CrNiBN coating was still better than that of CrBN coating indicating an improved corrosion inhibition efficiency by 12.53 times.