An investigation of the composition, structure, and electrochemical properties of carbon-nitrogen coatings on the surface of the carbon steel
Chemical composition of the surface layers on the carbon steel produced by the magnetron sputtering of carbon with subsequent ion implantation with nitrogen ions was investigated bwith the help of X-ray photoelectron spectroscopy. Electrochemical investigations were carried out in neutral borate-buffer solution, in decimolar solutions of alkali and acid in conditions of natural aeration. Decrease in the density of anode currents in the region of conditionally active dissolution as well as in the passive region of potentials has been ascertained. The protective property of the surface layers in an acidic environment can be attributed to the blocking of the active centers of the original surface. Electrochemical properties of the implanted surface with carbon and carbon-nitrogen coatings along with the properties of the carbon containing films and transition layers of nonstoichiometric Fe-C-N-O composition at the coating-metal interface is found to be play a significant part. In acidic media, the films formed do not exhibit a high cathode activity during hydrogen evolution whereas in alkaline media the synthesis of coatings with reduced overvoltage of hydrogen evolution is possible. It is established that the passive state of the steel with carbon-nitrogen coatings is associated not only with the presence of a dense surface layer based on disordered carbon but also with the formation of nonstoichiometric carbides, carbonitrides, or oxycarbonitrides of iron at the coating-metal interface. Surface layers formed in neutral and alkaline media contribute to the transition of the steel surface to the passive state.