Influence of negative voltage on the structure and properties of DLC films deposited on NiTi alloys by PBII

Diamond-like carbon (DLC) films have been successfully deposited on Ti-50.8 at.%Ni using plasma based ion implantation (PBII) technique. The influences of the pulsed negative bias voltage applied to the substrate from 12 kV to 40 kV on the structure, nano-indentation hardness and Young’s modulus are investigated by the X-ray photoelectron spectroscopy (XPS) and nano-indentation technique. The results show that C 1s peak depends heavily on the bias voltage. With the increase of bias voltage, the ratio of sp2/sp3 first decreases, reaching a minimum value at 20 kV, and then increases. The DLC coating deposited at 20 kV shows the highest hardness and elastic modulus values as a result of lower sp2/sp3 ratio. The corrosion resistance of specimen deposited under 20 kV is superior to uncoated NiTi alloy and slightly better than those of the other samples deposited at 12 kV, 30 kV and 40 kV.