Optimization of DLC films on oxynitriding-treated Vanadis 10 tool steel through the various duty cycles of DC-pulsed plasma-enhanced CVD

In this study, DLC films were coated on oxynitriding-treated Vanadis 10 tool steel using the DC-pulsed plasma CVD technique. The experimental parameters included different duty cycles (9, 13, 17, and 21 %) with asymmetric bipolar-pulsed voltages of -3 kV, a gas flow of CH4 maintained at 15 sccm, and a deposition time of 90 min. Meanwhile, the properties of DLC films were measured by Raman spectroscopy, Rockwell indentation, wear tests, FT-IR, corrosion tests, water contact angle tests, and four-point probes analysis. The experimental results showed that the optimum properties of DLC films occurred at a duty cycle of 17 %. It had the lowest wear volume loss for loads 2 N and 5 N were 3.49 x 10(-3) mm(3) and 4.08 x 10(-3) mm(3), respectively. Moreover, the optimal DLC films possessed the lowest corrosion current (I-corr = 7.91 x 10(-5) A cm(-2)) and highest polarization resistance (R-p = 1185.21 Omega cm(2)) in 3.5 wt.% NaCl solutions. The FT-IR spectrum analysis also found that the characteristic peaks of DLC films were generated at positions of 2852 and 2921 cm(-1), and the water contact angle tests showed that the DLC films had great hydrophobicity (78.33 degrees). Consequently, the results confirmed that the duplex surface treatment effectively improved the coating properties of Vanadis 10 tool steel.