Effect of C<sub>2</sub>H<sub>2</sub> Flow Rate on the Deposition of Zr-ZrC-ZrC/DLC Gradient Nano-Composite Film on Biomedical NiTi Alloy

Abstract

Zr-ZrC-ZrC/DLC gradient nano-composite films have been prepared on the NiTi substrates by the technique of plasma immersion ion implantation and deposition (PIIID) combining with plasma-enhanced chemical vapor deposition (PECVD). The influence of C2H2 flow rate ranging from 30 sccm to 50 sccm on the chemical structure, microstructure, mechanical properties and corrosion resistance of resulting thin films are investigated by Raman spectrum, XPS, XRD, friction coefficient test, nano-indentation, electrochemical corrosion test and atomic absorption spectrometry. XPS and XRD results indicate that on the outmost layer, the Zr ions are mixed with the DLC film and form ZrC phase, the binding energy of C 1s and the composition concentration of ZrC depend heavily on the C2H2 flow rate. With the increase of C2H2 flow rate, the content of ZrC and the ratio of carbon sp3/sp2 decreases. The nano-indentation and friction experiments indicate that the gradient composite film at 30 sccm has a higher hardness and lower friction coefficient compared with that of the bare TiNi alloy. The microscratch curve tests indicate that Zr-ZrC-ZrC/DLC gradient composite films have an excellent bonding property with the substrate. Based on the electrochemical measurement and ion releasing tests, we have found that the Zr-ZrC-ZrC/DLC gradient composite films exhibit better corrosion resistance property and higher depression ability for the Ni ion releasing from the NiTi substrate in the Hank’s solution at 37°C.