Microstructure and electrochemical characteristics of CrMoN/Ag nanocomposite coatings in seawater

CrMoN/Ag nanocomposite coatings with various Ag contents are deposited on Ti6Al4V alloys using closed-field magnetron sputtering, and their microstructures are detected by XRD, XPS and TEM. The electrochemical characteristics of CrMoN/Ag nanocomposite coatings are investigated using a three-electrode electrochemical workstation. The results show that the phase structure of coating contains (Cr, Mo)N solid solution and Ag crystallites. As the Ag content rises from 0.21 at.% to 4.86 at.%, the amount and size of Ag nanoparticle increase on the coating surface, and the cross-section feature of coating first becomes dense and then sparse. The corrosion resistance of coating in seawater is mainly dominated by its cross-section compactness and the amount of electrochemical active Ag. When the Ag content is 0.59 at.%, the dense cross-section and low surface roughness of coating contribute to its maximum open circuit potential of 0.173 V and charge transfer resistance Rct of 6.497 × 107 Ω∙cm2. But as the Ag content rises beyond 1.87 at.%, the potential drift range and power spectral density of coating gradually increase. Due to the occurrences of nanogalvanic corrosion and pitting corrosion, the corrosion resistance of coating is deteriorated, and then the corrosion current density icorr of coating continuously raises.