Synthesis and electrochemical characterization of multilayer ceramic metal coatings of W/WN, Ti/TiN and WTiN

Corrosion causes great losses and catastrophic damages in industrial plants and infrastructure, among the methods to reduce it are the coatings. The use of metal-ceramic multilayer coatings to reduce corrosion in steels is a viable option, since they offer several advantages over single-layer coatings, among which, they can be deposited with relatively high thicknesses and are able to dissipate the residual stresses that form during the growth of the thin films, which maintains its adhesion to the substrate. The coatings were deposited by magnetron sputtering, using Ti and W targets. Two multilayer architectures were designed and deposited, including tungsten nitride (WN) and titanium tungsten nitride (WTiN) coatings with alternated bilayers of Ti/TiN and W/WN, those two deposition sequences of layer were identified as A with more Ti and B layers with higher W content; both consist of a nine-layer deposit process. The structure was studied by X-ray diffraction and the morphology and composition by Sem and EDS respectively. The surface was studied with profilometry and atomic force microscopy. The electrochemical behavior was analyzed in a sodium chloride solution by means of potentiodynamic polarizations and electrochemical impedance spectroscopy (EIS). X-ray diffraction results show the presence of two phases of WN. The grain size of coating A is similar to that obtained in coating B. The morphology of the multilayers showed a mostly smooth surface but with the presence of spherical domes, as well as cracks in both coatings, being more abundant in the coating B. In its cross sections, the sequence of multilayers composed of layers of Ti, W, TiN, WTiN and WN is observed, however in some cases the change between the individual layers is not observed and two layers remain as one in the images of Sem. The electrochemical results obtained by potentiodynamic polarization curves showed a shift of the corrosion potential towards more noble values. The corrosion current in coating A with more layers of Ti is lower than coating B and both improve the corrosion resistance of the substrate. This behavior was confirmed in the Nyquist diagram obtained by EIS. (author)