Growth of a W/TiN-bilayer coating: an alternative to diffusion barrier keeping the hard coating condition of the system

An evaluation of the improvement provided by a W thin film, when incorporated into a TiN bilayer coating system on 304 stainless steel, is reported after determining its electrochemical behaviour and mechanical properties. The TiN-bilayer and W/TiN-bilayer coatings were prepared by balanced magnetron sputtering. Coating structure, morphology, interphase, and chemical composition were determined by scanning electron microscopy, Auger electron spectroscopy and X-ray diffraction. Mechanical properties were determined by the nanoindentation technique. The electrochemical behavior was investigated by electrochemical impedance spectroscopy (EIS) using 6 wt.% NaCl solution as electrolyte. The electrochemical results showed an increase in overall corrosion resistance (Rp) when the W thin film is incorporated into the TiN-bilayer coating system. The Rp for the initial measurement is 187.6 and 347.9 kΩ cm2 for the TiN-bilayer coating system and W/TiN-bilayer coating system, respectively. The results obtained from the EIS study over time indicate that the Rp after 7 weeks of immersion are 53.2 and 119.8 kΩ cm2 for the TiN-bilayer coating system and W/TiN-bilayer coating system, respectively. Nanoindentation hardness measurements showed a slight difference between the two coating systems. The TiN-bilayer hardness showed a value of approximately 24 GPa, while the W/TiN-bilayer hardness showed a value of approximately 22 GPa. Considering other beneficial properties associated with W, the results showed that a W/TiN-bilayer coating system can be used as an alternative hard and protective coating system on steel substrates to mitigate corrosion damage.