Effect of carbon content on the structural, mechanical and corrosion properties of TiC films deposited using a HiPIMS discharge

TiCx thin films have been deposited on steel substrates using High Power Impulse Magnetron Sputtering (HiPIMS) under Ar-C2H2 atmosphere. The effect of varying the acetylene content on the deposition process, and on the structural, mechanical and corrosion resistance properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, scratch testing, potentiodynamic polarization, electrochemical impedance measurements (EIS), and salt spray. This study showed that an increase of the carbon ratio affected the deposited Ti-C coatings morphology and mechanical properties, with hardness values reaching up to 25 GPa. The near-stoichiometric coating exhibited the highest hardness while maintaining improved toughness, resistance to plastic deformation and resistance against crack propagation thanks to their nanocomposite structure. In contrast, corrosion tests showed that the understoichiometric coatings exhibited the best corrosion resistance in a 3.5 % wt NaCl medium. The drop of the corrosion performances of TiCx coatings deposited at higher acetylene flow rate was linked to a growth-related defects extending throughout the coating thickness, formed due to micro-droplet ejection from the target as evidenced by SEM analysis.