Structural, mechanical and tribological behavior of different DLC films deposited on plasma nitrided CF170 steel

In order to improve the surface hardness and tribological properties of CF170 steel, a duplex treatment including plasma nitriding and deposition of different diamond-like carbon (DLC) films was carried out on CF170 steel. The structural, mechanical and tribological properties of untreated, plasma nitrided and duplex-treated samples were investigated by methods of XRD, SEM, AFM, Raman spectroscopy, XPS, hardness tester, scratch tester and ballon-disc tribometer, respectively. Raman spectroscopy and XPS revealed that the Ti/a-C/(ta-C) film had the highest amount of sp3 content, followed by Cr/WC/(a-C:H) and Cr/WC/(a-C:H:W) films. The hardness of duplextreated samples was significantly higher than that of single plasma nitrided sample and the highest value was obtained from the Ti/a-C/(ta-C) film deposited on the plasma nitrided sample. The critical adhesion load (Lc3) of the Cr/WC/(a-C:H) film deposited on the plasma nitrided sample was obviously higher than that of the Ti/a-C/ (ta-C) film deposited on the plasma nitrided sample. The duplex-treated samples showed a low friction coefficient. Both Cr/WC/(a-C:H) and Ti/a-C/(ta-C) films deposited on plasma nitrided samples had a low wear rate. The wear rate of the Cr/WC/(a-C:H) film deposited on the plasma nitrided sample was reduced by one (five) orders of magnitude compared to the plasma nitride (untreated) sample.