Characterization of the structure and electrochemical behavior of Ag-TaN nanostructured composite coating for biomedical applications

This work presents the development of a new Ta/TaN/TaN-Ag/TaN (hereinafter referred as Ag-TaN) multilayer coating system deposited by unbalanced magnetron sputtering technique on AISI 316L steel. The microstructure and electrochemical behavior of the coating in relation to the bias voltage (−30 V and −120 V) applied during the formation of the upper layer of TaN were studied. It was found that the structure, mechanical properties and silver release depend on the bias voltage applied, as this affects the degree of densification of the TaN diffusion layer. The multilayer coating exhibited high values for mechanical properties due, among other factors, to the obtained nanometric structure obtained and to the stress relief caused by the minimization of the defects, whereas doping with silver nanoclusters reduced the hardness of the coating. The Ag-TaN coatings presented superior electrochemical activity to the steel substrate and the TaN matrix coating, and consequently exhibited greater corrosion current densities. This behavior is correlated mainly with the dissolution of silver to the surrounding medium. The Ag-TaN(−30 V) composite coating provided the best mechanical properties and highest electrochemical activity and silver release, the last of these with maximum values of 0.23 μg/mL, lower than those reported as cytotoxic, making this multilayer useful for biomedical applications.