Research On Electrochemical Corrosion Behavior And Corrosion Control Of Dental Ti-Zr Alloys

Titanium and titanium alloys have many advantages,such as low density,high specific strength,lower modulus of elasticity closer to bone,excellent corrosion resistance,good biocompatibility and technological properties.When pure titanium is used as dental implant material,it will break due to insufficient mechanical strength.Ti-6Al-4V alloy dissolves Al and V ions which are toxic to human body during corrosion.Therefore,the exploration and development of the implant materials with low cost,high corrosion resistance and high loading and effective corrosion protection method for the implant materials is the main research direction in recent years.The corrosion resistance of Ti50Zr alloy with better mechanical properties than Ti16Zr alloy which has been used in the clinic has been explored in this paper.The surface morphology composition and chemical bond of Ti16Zr and Ti50Zr alloy after electrochemical corrosion and immersion test were characterized by SEM EDS and XPS.In addition,(Ti,Zr)N films with different nitrogen flow rates were prepared on Ti-Zr alloy substrates by magnetron sputtering.The mechanical properties of(Ti,Zr)N films were measured by XRD SEM EDS,videometer and automatic scratch instrument for coating.Nanometer gradient(Ti,Zr)N films were prepared by nitrogen flow with the best comprehensive mechanical properties.(Ti,Zr)N film was characterized by electrochemical method and immersion test and SEM EDS XPS.The experimental results show that:In the artificial saliva with different pH value(7.4 5.2 3.9 and 2.5)and fluorine content(0.05%0.1%and 0.15%),the passivation film formed on the surface of Ti-Zr alloys has strong stability low corrosion tendency and good corrosion resistance.The corrosion tendency of Ti-Zr alloys increase with the decrease of pH value and the increase of fluoride ion especially for the mass fraction of NaF is more than 0.1%.Ti50Zr alloy is more suitable for oral environment than Ti16Zr alloy in artificial saliva with the same pH value and fluoride concentration.Zr is preferentially passivates than Ti makes the ratio of ZrO2 in the passivation film increases with the increase of Zr content in Ti-Zr alloy.The composite passivation film contains ZrO2 and TiO2 has enhanced chemical stability and corrosion protection.The passivation films on the surface of Ti-Zr alloys is partialy corroded by reductive acid HF in the fluorinated artificial saliva with the pH value is 3.9.The annual corrosion rate of Ti50Zr alloy which is 0.099 mm/year is much lower than that of Ti16Zr alloy of 0.195 mm/year in the fluorinated artificial saliva of 0.05%with the pH value is 3,9.Ti-Zr alloy can be used in this oral environment and Ti50Zr alloy is more suitable than Ti16Zr alloy.However,the annual corrosion rate of the two alloys is over 0.574 mm/year when the concentration of fluoride is over 0.1%in the artificial saliva with the pH value is 3.9.The results show that Ti-Zr alloys is not suitable for oral environment with acid environment pH value is 3.9 and fluorine content more than 0.1%.The hardness of the(Ti,Zr)N film prepared by 14 sccm nitrogen flow rate is 35.3 GPa and the adhesion is 53.4 N as well as the microstructure is the most uniform and compact which can meet the requirements of corrosion and wear resistance of dental materials.Corrosion rate of alloy was reduced by 62.6%in artificial saliva with pH value is 5.2 and 78.6%in artificial saliva with pH value is 2.5.Corrosion rate of alloy was reduced by 61.5%in artificial saliva with the concentration of fluoride is 0.1%and 62.4%in artificial saliva with the concentration of fluoride is 0.15%.The results show that(Ti,Zr)N film acts as a barrier between Ti-Zr alloy substrate and corrosion solution.The good passivation property of the film improves its chemical stability and effectively enhances its corrosion resistance.Reductive acid HF destroys the passive film contions TiO2 ZrO2 TiN and ZrN on the surface of the film in artificial saliva with low pH value of 3.9 and high fluoride concentration of 0.1%or 0.15%.Furthermore,Fluorine ion diffuses and penetrates through the defects such as micropores and pores in the film to the interface between the alloy substrate and the film,which leads to the corrosion of the alloy substrate and reducing the impedance of the alloy-film system.