Electrochemical behavior of superhard nanocomposite coatings of TiN/Si3N4 prepared by reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of TiN/Si3N4 are new generation superhard coatings having hardness greater than 40 GPa. Apart from high hardness, these coatings exhibit outstanding properties such as improved wear resistance and high oxidation resistance. These coatings also retain their hardness even after heating in air at higher temperatures. The present study reports electrochemical behavior of superhard nanocomposite coatings of TiN/Si3N4 in 3.5% NaCl solution. The nanocomposite coatings with varying silicon contents have been prepared on steel substrates by reactive direct current unbalanced magnetron sputtering. Single-component TiN and Si3N4 coatings have also been included in the investigation. The electrochemical measurements were performed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corroded samples were characterized using scanning electron microscopy and energy dispersive X-ray analysis. The nanocomposite coatings exhibited better corrosion resistance than single-phase TiN coatings. Nyquist and Bode plots obtained from the EIS measurements for bare steel substrate, single-component TiN and nanocomposite coatings were used for evaluating the corrosion behavior. The charge transfer resistance and the double layer capacitance were also calculated using EIS data.