Electrochemical corrosion of titanium and titanium-based alloys

Statement of problem. Two varieties of unalloyed titanium, Ti-6Al-4V and Ni Ti, commonly are used in medical and dental fields. Several other types of alloys for potential use in these fields have been developed, including Ti- 4.5Al-3V-2Mo-2Fe and vanadium-free alloys (Ti-5Al-2.5Fe and Ti-5Al-3Mo-4Zr) . The corrosion of these alloys under simulated physiologic conditions is n ot known. Purpose. This study compared the corrosion behaviors of 6 titanium material s through electrochemical polarization tests in 37 degreesC Ringer's soluti on. Material and methods. The applied voltage was potentiostatically scanned fr om -0.6 to 1.0 V. From polarization curves, the corrosion rate (averaged ov er 3 samples) for each alloy was calculated and compared with that of other alloys. Analysis of variance (ANOVA) and the Student-Newman-Keuls multiple range test were performed at a 95% overall confidence level to identify st atistically significance differences in corrosion rates. Surface oxide film s were identified by electron diffraction, and the electrolyte medium was a nalyzed by atomic absorption spectrophotometry after each alloy was tested. Results. Commercially pure titanium and Ti-5Al-2.5Fe were the most resistan t to corrosion; Ti-5Al-3Mo-4Zr, Ti-6Al-4V, and NiTi were the least resistan t to corrosion. NiTi exhibited pitting corrosion along with transpassivatio n. Conclusion. Electron diffraction patterns indicated that all titanium alloy s were covered mainly with rutile-type oxide (TiO2) after corrosion tests. The oxides that formed on Ti-5Al-2.5Fe were identified as a mixture of TiO2 and Ti9O17, and those that formed on NiTi were identified as a mixture of TiO2 and Ni2Ti4O.