Research On Electropolishing And Corrosion Behavior Of Anodized Titanium

Titanium and titanium alloy are widely used in biomedical materials due to their biocompatibility, excellent corrosion resistance, good mechanical properties and lightness. However, there are some problems need to be solved right now. Such as the corrosion resistance of titanium should be improved. The surface property of titanium is related to these problems. Electropolishing and anodizing are both important surface technologies for titanium, which are good ways to improve the corrosion resistence of titanium. In addition, titanium has a good prospect of application in aviation, military, chemical industry and oceamcs.In this paper, a new environmental friendly and non-toxic electropolishing technology was proposed. Surface brightness, roughness and surface modality were main standard used for study the condition. We used potentiodynamic polarization curve, roughness reader and SEM to study the influence of voltage, time, temperature and distance between electrodes. What's more, we compared electropolishing technology with the traditional mechanical polishing and chemical polishing. The results showed that titanium after electropolishing got more smooth surface and was mirror like. The roughness of surface was about 0.09μm, which also had lower icorr, thus showed better corrosion resistance. The optimal condition was 30V, 180s,50℃and 2cm.The corrosion behavior of titanium and after anodizing in H2SO4 and H3PO4 was studied by potentiodynamic polarization curve, EIS and Mott-Schottky plots in physiological saline solution. And the corrosion behavior of titanium after anodizing in (NH4)2SO4, H2SO4 and H3PO4 was investigated by potentiodynamic polarization curve, EIS in Br- containing acetic acid solution. The results indicated that titanium after anodizing showed higher self-corrosion potential, lower icorr. Compared with the blank sample, the corrosion resistance were improved largely when titanium after anodizing. EIS exhibited higher impedence values in the low frequency range for films anodized in phosphoric acid. Meanwhile the Mott-Schottky plots showed lower donor density and lower flat band potential for titanium anodized in H3PO4, which reflected better corrosion resistance than titanium anodized in H2SO4. The breakdown potential of the pitting is observed for blank sample in Br- containing acetic acid solution. But it was not found when titanium after anodizing in (NH4)2SO4, H2SO4 and H3PO4. It was also found that the color and thickness of the film were changed with the voltage except the corrosion behavior.The galvanic corrosion generated between titanium after anodizing and carbon steel pair in area ratio at 8:1 for 8 hours in simulate seawater was studied by CS300. Compared with the blank sample, the results showed that galvanic current densities were reduced largely after titanium anodizing. Galvanic current densities was 175μA for blank sample galvanic pair. Galvanic current densities was 40μA for titanium anodizing in H3PO4 for 40V and 80μA for titanium anodizing in H2SO4 for 40V. The anodic oxide films lead to an IR drop in the system.