Detailed study of the electrochemical behavior of low-reflectivity TiAlN coatings

Titanium aluminum nitride (TiAlN) is proposed as a coating to decrease the reflectivity of surgical instrumentation, thereby improving the field of vision of surgeons during procedures, although the corrosion resistance of the material against repeated sterilization processes must be guaranteed. The influence of aluminum (Al) on the microstructural and electrochemical properties of low-reflectivity titanium aluminum nitride coatings deposited by direct-current unbalanced magnetron sputtering was evaluated. The optical properties, chemical phases and composition were determined using the ultraviolet–visible spectroscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques. The microstructures were analyzed by atomic force microscopy, scanning electron microscopy and transmission electron microscopy–selected area electron diffraction. The corrosion resistance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization. It was found that an increase in the aluminum content reduced the coating reflectivity by 60%, showing a dense columnar crystalline structure with a grain size of 200–100 nm and roughness of 6.7–4.0 nm and the coexistence of titanium nitride (TiN), aluminum nitride (AlN), titanium aluminum nitride and aluminum oxide (Al₂O₃) phases. In comparison with AISI 420 steel, the TiAlN-1300W aluminum coating showed a more positive corrosion potential, as well as a current density two orders of magnitude lower, thus guaranteeing corrosion resistance.