SURFACE STRUCTURE OF TIN/TI MULTI-LAYERED THIN FILMS DEPOSITED ONTO Ti-6Al-4V ALLOY BY MAGNETRON SPUTTERING

Ti-6Al-4V alloy attracting attention as a biomaterial features excellent mechanical properties and corrosion resistance, and super plasticity, so enables the forming of denture bases of complicated shapes. However, this alloy contains aluminum and vanadium liable to do serious harm to human bodies [1,2], so actual use will require prevention of direct contact with biological tissues. In our previous study, a method of coating the alloy surface with pure titanium film of excellent biocompatibility as a barrier layer was developed by DC sputtering in argon atmosphere, to improve the dental applicability of the alloy [3]. The pure titanium barrier layer prevents such harmful substances from leaching out to biological tissues. The alloy coated with titanium layer is, however, not suitable for the medical materials exposed to the blood stream such as artificial heart valves, because titanium is not only poor in the blood compatibility but also soft and easily damaged [4]. Hence, it is necessary to improve both the hardness and the blood compatibility of the barrier layer. Y.Mitamura, et al. reported the good blood compatibility of titanium nitride films [5]. Therefore, the deposition of TiN/Ti multilayered thin films onto Ti-6Al-4V alloy substrates by magnetron sputtering in Ar gas atmosphere was examined, aiming at the application of pure titanium to the material for totally implantable artificial hearts, in order to improve not only the adhesion between the deposited film and the alloy but also the surface smoothness of titanium nitride coatings and thereby the blood compatibility of the alloy coated with the titanium nitride film. The effects of the thickness of the TiN(titanium nitride) layer on the surface structure of the multi-layered film were investigated, in order to develop TiN coatings with higher blood compatibility [6].