The Study And Evaluation Of Multi-layer Films Preparation On Surface Of Nickel Titanium Alloy

The NiTi shape memory alloys (SMA) are already gradually used to implant into the human body as one part of people's hard organization. As implanted materials, The NiTi shape memory alloys mainly face two problems, one is unsatisfactory mechanicl performance and biocompatibility resulting from the big difference between their elastic modulus and the bone's which would cause stresses concentration and effects bone absorbing capacity. The other is the NiTi SMA are of biological inertia in that ingredient and organizational structure of the NiTi SMA differ from the human bone. So implanting in vivo is just interpreted to link the bones together by machinery inlays. Therefore it is extremely essential to make surface modification of the Titanium and its alloys.Research on the diamond like-carbon film develops rapidly in recent years. The performance of DLC film cannot satisfy the implanting need only prepared by the physical gas phase deposition or chemistry gas phase deposition technology for the medical metallic material. The binding force between the thin film and the medical metal material is weak owing to high internal stress between the thin filem and the substrate whereas thin film and the substrate ia various in heat expansion performance, concequencely the thin film could appear flaking off, corrugating phenomenon and so on in the their applications. In this experiment the author adopted graded films technology and prepared graded Diamond-like Carbon (DLC) film utilizing the twinned microwave-ECR plasma source combing compound Physical Vapor Deposition (PVD) methods. So far, the Si/(Si/ α -C:H) transitional layer has deposited successively in the NiTi substrate, then the graded DLC film is prepared subsequently, a reasonable technologic parameter is expected to advice graded diamond preparation. The test results showed that the Si graded layer deposited in 60 min provided the best adhesion strength between the graded DLC film and NiTi alloy substrate. There existed poor adhesion between graded DLC films and NiTi alloy substrate once the deposition time was above or under the value.At precent the hydroxyapatite was considered one of the best biologic ceramics which possesses good biologic compatibility, however the domestic and foreign researchers mainly concern the sole HA coating. When metal substrate and the coating are heated or cooled there would cause remanent stress to weaken the adhesive strength between them on account of their various expansion coefficients. Hence, it is desiderated to improve the adhesive strengthof the coatings and ensure its stable existing in in the body in order to enable the material to satisfying the clinical practical needs. For instance, Titamium oxide films formed on the nickel titanium alloy surface could effectively improve the corrosive nature and the attrition performance, and further forms a barrier between the human body and the nickel ion of alloy which prevents the nickel ion entering into the human body. In this paper the titamium oxide and hydroxyapatite films has been prepared successively with the sol-gel method, then TiO2/HA biological activity film is prepared after the author integrates the respective strongpoints of titamium oxide and hydroxyapatite. The test results showed that the HA/TiO2/NiTi system has better corrosion behavior and bonding strength than puer HA/NiTi system.The results of this research indicate that it is necessary to introduce transitional and buffer layer between the thin film and the substrate to reduces stress regardless of preparation the hydroxyapatite film or grated diamond like-carbon film.