Study On Biomedical Film By The Technique Of Plasma Surface Modification On NiTi Alloy

The purpose of the present study is to improve the hardness, wear resistance, anticorrosion and hemocompatibility by treating the surface of NiTi alloy using microwave plasma modification technique. The relationship between the surface modification treatment parmeters and the resulted perforeance of the film were studied by AFM, XPS, XRD, Raman spectrum, TEM, nano-indentation tests, adhesion tests, friction coefficient tests, electrochemical measurement and hemocompatibility experiments.Zr films were prepared by plasma immersion ion implantation and deposition (PIIID) technique. AFM results indicate that the Zr films have columnar structure. With the increase of the implantation voltage, the root-mean-square roughness (RMS) of Zr films almost don't change. The electrochemical measurement tests show that the implantation voltage and sputtering current have decisive influence on the corrosion resistance of Zr films. The higher the implantation voltage and the sputtering current, the better of corrosion resistance.Using plasma immersion ion implantation (PIIID) and deposition combining with plasma-enhanced chemical vapor deposition (PECVD) method, the gradient nano-composite Zr-ZrC-ZrC/DLC films and Ti-TiC-TiC/DLC gradient nano-composite films were prepared on NiTi alloy. Raman spectra and XPS results indicate that the doped carbon films still have the amorphous DLC structure. XRD and TEM detected nano-carbide which is enchased by the amorphous DLC in the deposited layer. AFM results indicate that the Zr-ZrC-ZrC/DLC films have the columnar structure, but the Ti-TiC-TiC/DLC films have the layer structure and the lower RMS value. It indicates that the doped element is the decisive factor for the film structure. From the adhesion tests and friction coefficient tests we can find that the Zr-ZrC-ZrC/DLC films have the better bond strength than Ti-TiC-TiC/DLC films, but the Ti-TiC-TiC/DLC films have the lower friction coefficient. The nano-indentation results show through changing the deposited voltage and C₂H₂ gas flux rate could increase the hardness and elastic modulus of the films. Electrochemical measurement show that the corrosion resistance of Zr-ZrC-ZrC/DLC films were determined by the deposited voltage and C₂H₂ gas flux rate and all the Ti-TiC-TiC/DLC films have a remarkable corrosion resistance due to the layer structure of the films.The platelet adsorption tests show that the modification films improve the hemocompatiblity of NiTi alloy.