| NiTi alloy has been widely used in implantable and interventional medical field for its excellent corrosion resistance, shape memory properties and biological properties. However, Ni Ti alloy contains about50at% of the nicke, which will induce toxicity, cell distortion, even carcinogenic once dissoved into the biological environment. Therefore,surface modification treatment is necessary to reduce the harm of the overflow of nickel ions to the human body, and improve the mechanical and biological properties.In this paper, dealloying technology was used to prepare a Ni-free layer with a certain depth on the surface of Ni Ti alloy. Anodic oxidation technology was used to prepare Ti O2 films on the surface of Ni Ti alloy in different electrolyte solutions, and this technique was used on the Ni-free layer of Ni Ti alloy. Ultrasonic phosphating technology was used to prepare phosphating films on the surface of Ni Ti alloy.The surface morphology, structure, film thickness, wear resistance,corrosion resistance and biological properties of Ni Ti alloy treated by different surface treatments were studied using scanning electron microscope(SEM), X-ray diffraction(XRD), inverted optical microscope,friction and wear tester, electrochemical workstation, X-ray photoelectron spectroscopy(XPS) and other equipments.The results show that, the optimal formula and technological parameters of dealloying treatment is: H2O2 10%+ Na Cl 0.5mol/L, p H=4.5,T=70℃, t=3h. A Ni-free layer of porous nano grid structure with a certain thickness is formed on the surface of the dealloyed Ni Ti alloy. The optimal formula and technological parameters of anodic oxidation treatment is:Na2SO4 0.02mol/L+Na Cl 0.10mol/L+Citric acid 4.2g/L, p H=3, t=25min,room temperature, constant current of 0.1A, and the thickness is about4.5μm. The structure of Ni-free layer and anodic oxidation Ti O2 film are both single rutile-Ti O2 after annealing treatment at 800 ℃. The optimal process parameters of ultrasonic phosphating treatment is: activation time of 30 s, UI power of 180 W, phosphating temperature of 80℃, phosphating time of 1h. The phosphating film, with a small and short rod, is uniform,compact and complete, and the thickness is about 17.5μm.Compared with Ni Ti alloy substrate, the self-corrosion potential of composite films(Ni-free layer+anodic oxidation Ti O2 film) and phosphating film is improved significantly, and the self-corrosion current density reduced by 2 orders of magnitude, showing good corrosion resistance. Phosphating film prepared by ultrasonic phosphating treatment has a stable and low coefficient of friction, about 0.12, compared to 0.50 of the Ni Ti alloy substrate, showing excellent wear resistance. Apatite can be induced on the surface of different modified samples, the adsorption of apatite on the surface of the composite films is dense, the Ca/P atom ratio(1.52) is closest to 1.67, which shows good biological activity. The anticoagulant property of Ni Ti alloy can be improved after different modification treatments, the clotting time of the composite films lengthens to more than 60 minutes, the O.D. value decreases slowly, and the release of Ni ions socked in SBF for 14 day is reduced by 1.161μg/m L, which shows good anticoagulant property and biocompatibility. |
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