Microstructural and electrochemical properties of TiAlN(Ag,Cu) nanocomposite coatings for medical applications deposited by DC magnetron sputtering

AISI 420 stainless steel is currently used in the manufacture of surgical and dental instrumentation due to its hardenability, acceptable biocompatibility and resistance to corrosion. However, its resistance to wear is relatively low, and therefore multiple strategies of surface modification are used in order to overcome these drawbacks in the properties of this material when envisaging its use for biomedical applications. In this work, TiAlN coatings doped with Ag and Cu nanoparticles in four different quantities (11 at.% to 20 at.%) were deposited onto 420 steel by DC magnetron sputtering technique. The microstructure, and chemical and phase composition were analyzed by scanning and transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction, while roughness was determined using atomic force microscopy (AFM). The electrochemical behavior of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The analysis of the microstructures of the different coatings revealed that the typical columnar structure of the TiAlN matrix is densified as the content of silver and copper increases. The Ag and Cu doping materials are placed in the free spaces between the grain limits of the TiAlN structure due to their insolubility in the ceramic matrix. Additionally, a concomitant increase in the amount and size of the Ag and Cu nanoparticles present on the coating surface was evidenced as the power applied to the target was raised. A reduction in the corrosion current density of the steel substrate was evident once it was superficially modified with the TiAlN matrix coating, which formed a protective barrier to the corrosive medium. The TiAlN(Ag,Cu) coatings developed superior electrochemical activity with respect to the TiAlN matrix, and consequently exhibited higher corrosion current densities. This behavior was accentuated with increased Ag/Cu content in the coating, and it was correlated mainly with the increase in the dissolution rates of silver and copper to the surrounding medium. This suggests a potential bactericidal effect of this kind of coating, which might be considered for potential application in surgical and dental instrumentation. © 2020