Correlation between the duty cycle and the surface characteristics for the nanostructured titanium aluminum nitride coating deposited by pulsed-DC PACVD technique

The purpose of this paper is to investigate the relation between duty cycle, microstructure and surface properties of the nanostructured titanium-aluminum nitride (TiAlN) coatings produced by using pulsed-DC plasma-assisted chemical vapor deposition (PACVD). In order to evaluate the effects of duty cycle, TiAlN coatings were applied for 150 min in the 30, 40, and 50% of duty cycle at 470 °C substrate temperature, 10 kHz frequency, and 3 mbar working pressure. Field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and Energy-dispersive X-ray spectroscopy (EDS) were used for the coatings characterization. To evaluate the coatings surface properties, Nano-indentation, residual stress tester, Tafel polarization, and electrochemical impedance spectroscopy (EIS) were also utilized. The results implied that microstructure and mechanical properties of the coating have a significant correlation with duty cycle. Due to the fact that nucleation and growth occurs in the off-time, with decrease in duty cycle, the number of nuclei significantly increases. So, when duty cycle declined from 50 to 30%, coating nano-hardness increased from 26 to 31 GPa. Furthermore, corrosion behavior showed that the polarization resistance of the coating deposited at 30% duty cycle, is the highest value in complete accordance with the obtained results from tafel polarization curves (the least corrosion current density).