Preparation And Mechanical Properties Of TiN Compositional Gradient Films By Reactive Sputtering

Titanium alloys are of excellent structural functional and biomedical material and have been wildly used as biomedical implantes. To date, more than80%biomedical implants are made of Ti6A14V (a-type) alloys. Due to low hardness and poor wear resistance of Ti6A14V alloys, surface modifications via nitriding are the prerequisites for the application of Ti6A14V as biomedical implants. Whereas, owing to the inhomogenity of TiN layer and Ti6A14V there will be a distinct interface between the two parts, which decreased the adhesion strength. The adhesion strength between the TiN layer and Ti6A14V alloys should be further improved. Therefore, the main movitation of this work is to find an effective approach that can further improve the adhesion strength between the TiN layer and Ti6A14V alloys.A series of TiN monolayed films, TiN compositioned gradient films and TiN/Ti multilayed films were prepared by reaction magention sputtering on Ti6A14V substrate. The crystal structures, surface morphology and cross-sectional microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microhardness of TiN film was measured by401MVDTM Microhardness tester. WS-2005scratch test apparatus was used to evaluate the adhesive strength between films and substrate. The main results are as follows:(1) For the single layer TiN films, the influence of sputtering parameters such as working pressure and nitrogen content on structural and mechanical properties were investigated. With increasement of the working pressure, the color of TiN thin films was deepened. The grain size of TiN thin films was also decreased. The results show the good crystallinity of TiN thin films was obtained at low pressures (0.05Pa).With the increasing of nitrogen flow rate, the color of TiN thin films was also deepened and the changed from silvery to black. The nitrogen content of the TiN thin films was increased too. With the thickness of films increased from600nm to3600rm, the hardness of TiN film was increased from636.5HV to2089HV, and the adhesion of TiN film was increased from32N to43N. The results show good crystallinity and compact density.It is beneficial for increasing crystallization and compact density of TiN thin film at high temperature environment. With the substrate temperature increased from Ambient temperature to340℃, TiN film adhesion on substrate was increased from10N to43N, TiN film hardness increased from1048HV to1360HV.TiN thin films mechanical properties were improved by suitable target-substrate distance.With the target-substrate distance decreased, adhesion of film on substrate was increased to60N, hardness of thin films was increased to1271.5HV. The results show that it is good crystallinity and compact density of TiN films, depositioned at100mm between target and substrate.(2) A series of TiN compositioned gradient films were prepared on the surface of Ti6A14V substrate, there are three kinds of phase appeared, namely Ti, TiN, Ti2N. with the gradient thickness increased, compact density is better. For the case of hardness and adhesion of TiN thin films, there is a clear increase with increasing gradient thickness up to1200nm, followed by a slight decrease for higher gradient thickness. Based on adhesion and hardness measurements on both TiN bilayered and compositional gradient films, it can be concluded that the compositional gradient films can significantly enhance the mechanical properties than bilayered films.(3) With the modulation ratio changed from1:9to1:2, there were Ti, TiN, and Ti2N three kinds of phase appeared. For the case of hardness and adhesion of TiN/Ti multilayered films, there is a clear increase with the modulation ratio changed from1:9to1:2. Compared with TiN monolayer films, hardness of TiN/Ti multilayered films is increased by about250HV and adhesion is increased by22N. The mechanical properties of TiN/Ti multilayered films are better than monolayer films. When modulation cycle is30layers, hardness of TiN/Ti multilayered films is1675.8HV and adhesion is60N. Compared with monolayer films, the hardness is increased by almost300HV and adhesion is increased by22N.