Investigation On Corrosion Behavior Of Ultrafine-grained CP-Tiand CP-Zr Processed By ECAP+Rotary Swaging

The grain refinement of the materials can not only improve the material mechanical performance but also increase the corrosion resistance.Research on the corrosion behavior of ultra-fine grain（UFG）CP-Ti and CP-Zr in simulated oral saliva is important for expanding the scope of the oral implant materials.In the paper,CP-Ti,CP-Zr and UFG CP-Ti and CP-Zr processed by ECAP+Rotary Swaging were used as experimental materials.The main research content and results are as follows.Orthogonal experimental design was carried out on CP-Ti and CP-Zr in the simulated oral saliva with different pH and fluorine ion concentration.The corrosion rate of materials was used as the test evaluation index.The experimental data was analyzed by visual analysis,the effect of curve,variance analysis and potentiodynamic polarization curve.The orthogonal experimental results are as follows.（1）Fluorine ion concentration is the most obvious influence factor on the corrosion rate of materials,and the pH has the least influence.The main reason is that fluorine ion can form hydrofluoric acid in the acid solution which can destroy material surface passive film.（2）With the increase of fluorine ion concentration and the decrease of the pH,the corrosion rate of materials increases.The corrosion rates of ultrafine-grained materials are less than those of coarse grained counterparts and the corrosion rates of CP-Ti are less than that of the CP-Zr.The corrosion behaviors of research materials in simulated oral saliva at pH 6.8and fluoride concentration 0.3 g/L were analyzed by the open circuit potential,potentiodynamic polarization curve,electrochemical impedance spectroscopy and scanning electron microscopy（SEM）and X-ray pHotoelectron spectroscopy（XPS）on the corrosion morpHology.The main research results are as follows.（1）The corrosion resistance of CP-Ti and CP-Zr in simulated oral saliva is improved after ECAP+rotary swaging.Compared with the CP-Zr,the CP-Ti has more positive open circuit potential,the smaller corrosion current density,and the greater polarization resistance.It means that the corrosion resistance for CP-Ti is better than that of CP-Zr.（2）The corrosion morpHology indicates that CP-Ti surface is smooth and no obvious corrosion pits while corrosion surface of UFG CP-Zr appeared obvious corrosion pits and coarse grained CP-Zr occurs general corrosion.（3）The peak and unimodal analysis on corrosion surface of the material using XPS.The main component of passive films in CP-Ti and CP-Zr is TiO₂ and ZrO₂,respectively.NaF and ZrF₄ exit after corrosion in CP-Ti amd CP-Zr,respectively.The results show that fluorine ions have more influence on the corrosion properties of CP-Zr in simulated oral saliva.