| TiNi alloy not only has unique shape memory effect and hyperelasticity,but also shows excellent biocompatibility,corrosion resistance and wear resistance,and is widely used in biomedical fields.TiNi alloy shows excellent adaptability and high resilience when used as orthodontic arch wire,and releases sustained force on teeth during orthodontic treatment.In the process of tooth correction,friction and resistance will inevitably occur between the arch wire and the brackets.The friction between the arch wire and the brackets will reduce the movement efficiency of the teeth,and the teeth will not be able to move.Therefore,it is necessary to reduce the friction coefficient of the orthodontic archwire in order to obtain better correction effect.In this paper,plasma immersion ion implantation was used to reduce the friction coefficient of TiNi alloy by injecting nitrogen ions on the surface of TiNi alloy,so as to obtain a better therapeutic effect.At present,high temperature and long time nitrogen ion implantation are used on TiNi alloys to meet the needs of industrial applications.After high temperature and long time nitrogen ion implantation,TiNi alloy will produce golden titanium nitride.The golden archwire is not beautiful.In addition,there is no strong friction and wear in the oral cavity of the archwire,so it is uneconomical and unsuitable to inject at high temperature and for a long time.Small dose of nitrogen ion injection at low temperature can reduce the cost and does not affect the appearance.In this study,different nitrogen ion implantation process parameters will be adopted to reduce the friction coefficient of TiNi arch wire while ensuring the color of TiNi arch wire remains unchanged.The effects of nitrogen ion implantation on the microstructure,mechanical properties and tribological properties of TiNi alloy were investigated by X-ray photoelectron spectroscopy,atomic force microscopy,nano-indentation,tensile test,balldisc friction and wear test and scanning electron microscopy.The experimental results show that titanium oxides,nitrogen oxides of titanium and titanium nitride are generated at the same injection dose and different injection frequency.The surface roughness of the samples decreased and the lowest value was 1.89 nm at the injection frequency of 150 Hz.The nanometer hardness decreased with the increase of injection frequency.The elastic modulus of the samples increased.After nitrogen ion implantation,the sample still maintains good superelasticity.When the injection frequency is 150 Hz,the friction coefficient of the sample decreases to 0.15 and the wear resistance is the best.With the injection frequency of 150 Hz unchanged and the injection dose increased,the surface phase composition remained titanium oxides,nitrogen oxides of titanium and titanium nitride.The roughness of the sample increased gradually with the increase of injection time,and the roughness of the sample was 3.1 nm when the injection time was 30 min,which was still lower than that of the sample without injection.After nitrogen ion implantation,the nano hardness of the sample increased gradually and the sample still maintained good superelasticity.With the increase of injection time,the wear resistance also gradually improved,and the sample with injection time of 30 min had the best wear resistance.In this paper,the optimal process parameters for nitrogen ion implantation of TiNi alloy were determined based on various analysis and test results: injection voltage-25 k V,pulse frequency 150 Hz,pulse width 15 ?s,nitrogen pressure 0.2 Pa,injection time 30 min.Under these parameters,the friction coefficient of TiNi alloy in artificial saliva was0.3 lower than that of the uninjected sample.The surface color of TiNi alloy did not change,and it was still metallic luster. |
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