| NiTi alloy has been widely used in numerous engineering field due to their unique shape memory effect,superelasticity and low elastic modulus.However,when used as biomedical materials,it can trigger adverse reactions to human system because of its lower hardness and the toxicity of nickel ions.In addition,as the implant material,excessive corrosion and wear at the implant surfaces exacerbate the release of Ni ions,reducing the use of NiTi alloy safety.Therefore,in order to improve the wear resistance and corrosion resistance of NiTi alloy and reduce the release of nickel element,the Ti alloyed layer was prepared on the surface of NiTi alloy by double glow plasma alloying technique.The effects of different holding temperature and different working pressure on the alloyed layer were studied by SEM,EDS,GDOES,XRD and other methods.The mechanical properties of the alloyed layer were analyzed.On this basis,the porous Al2O3 ceramic film was prepared by micro-arc oxidation on the surface of the Ti alloyed layer.The surface morphology,composition and structure of the Al2O3 ceramic film were systematically studied.The corrosion resistance and the wear resistance in the dry friction and simulated body fluids of the Ti alloyed layer and the Al2O3 ceramic film was studied by electrochemical test technique and sliding friction test,which lays a theoretical foundation for the application of NiTi alloy in engineering and biomedical field.Uniform and dense Ti alloyed layer was prepared on the surface of NiTi alloy by double glow plasma alloying technique.The Ti alloyed layer was composed of two layers,namely,the deposited layer and the diffusion layer.The process parameters were optimized,which were insulation temperature 875-900 ?,working pressure 35-40 Pa,pole spacing 18-19 mm,holding time 3h,alloying time 3 h,voltage difference 250 V.The mechanical properties of the Ti alloy layer were obviously improved.The hardness of the sample was more than 1400 HV0.025 at 900 and 40 Pa,and the hardness of the other process were more than 700 HV0.025.The Ti alloy layer was metallurgically bonded to the substrate,and the critical load of the alloyed layer peeling was more than 180 N.The electrochemical properties of the Ti alloyed layer were analyzed by the potentiodynamic polarization curve and the impedance spectrum.The corrosion current density of the Ti alloyed layer at different temperatures and different pressures was significantly decreased and the polarization resistance was significantly improved.The impedance and the phase angle of the Ti alloyed layer were higher than that of the substrate.The infiltration of Ti alloy layer improves the corrosion resistance of Ni Ti alloy.The Ti alloyed layer obviously improve the corrosion resistance of NiTi alloy.The wear resistance of NiTi alloy was improved obviously.Under the condition of dry friction,the specific wear rate of the Ti alloyed layer at 900 ? and 35 Pa was the lowest,which was only 15.8% of the wear rate of the substrate.The wear mechanism of the Ti alloyed layer under dry friction was mainly abrasive wear,adhesive wear and oxidation wear.In the simulated body fluid,the wear rate of the Ti alloyed layer was the lowest at 875 ? and 35 Pa.The wear mechanism of the Ti alloy layer in the simulated body fluid was mainly abrasive wear and slight oxidation wear.The porous ceramic film was prepared by micro-arc oxidation on the surface of the Ni Ti substrate and the Ti alloyed layer.The film was mainly composed of ?-Al2O3 phase.Polarization curve analysis shows that the corrosion potential of the ceramic layer of the Ti alloy layer was increased by 62.87% and the corrosion current density is 24.03% lower than that of the NiTi ceramic layer.Compared with the substrate,the corrosion potential of the ceramic layer of the Ti alloyed layer was increased by 44.34% and the corrosion current density was reduced by 99.01%.The micro-arc oxidation film can improve the corrosion resistance of NiTi,and the ceramic film prepared on the surface of the Ti alloyed layer sample has better corrosion performance.The preparation of the ceramic film on the surface of the Ti alloyed layer by micro-arc oxidation can significantly improve the wear resistance of the material under dry friction conditions and simulated body fluids.The wear mechanism was mainly adhesive wear. |
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