| Nickel-titanium shape memory alloy (NiTi SMA) is one kind of new functional materials.And it has been widely used in biomedical field due to its shape memory effect, superelasticity,good corrosion resistance and biocompatibility. To avoid the possibility of biological incompatibility and cytotoxicity, the technology of surface modification has been employed to treat the surface of alloy, contributing to better biocompatibility,higher orrosion resistance and wear resistance than the matrix, at the same time of reducing nickel ion precipitation.In this study, a layer of oxide layer was firstly prepared by surface oxidation. Compared with the result of the chemical oxidation and high temperature oxidation, the high temperature oxidation was chosen due to the high oxygen content of its surface oxide layer. Then, the alloy was treated by silane coupling agent. Finally, the blend polymer coating of EP/PTFE was sprayed on the surface of the alloy by using air compressor connected with the high atomization pneumatic spray gun. It can ensure the adhesion of the coatings, improving various mechanical properties of the surface coating. The thickness of the coating sprayed can be up to a few microns, it greatly reduces the thickness of the coating.In this study, effects of the surface chemical composition, morphology, roughness and oxide thickness on adhesion between the NiTi SMA substrate and the coating were studied.The adhesion could be improved significantly comparing to unoxidized NiTi SMA substrates.A heating temperature of 600? was determined to be optimal in the range of 300-700? for preparing bioactive NiTi SMA substrates presenting the highest adhesion. Meanwhile, the isothermal oxidation behavior of the NiTi SMA substrates possesses the highest adhesion with a duration time of 30 min under 600?. Finally, it has been found that the adhesion is strongly related to the high surface oxygen content, uniform morphology, appropriate roughness and oxide thickness. |
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