Corrosion Behavior of Cast Ti-Al and Ti-Al-Cu Alloys

Objective: This study examined the corrosion behavior of a series of Ti-Al and Ti-Al-Cu alloys. Methods: Five binary Ti-Al (5-9 mass%) alloys and six ternary Ti-Al (5 and 6 mass%)-Cu (1, 3 and 5.0 mass%) alloys were prepared in an argon-arc melting furnace. Each alloy specimen (10 mm x 10 mm x 2 mm) was cast using a centrifugal casting system (Ticast Super R, Selec, Osaka, Japan) with a MgO-based investment (Selevest CB, Selec). Specimens with ground surfaces (approximately 30 µm removed from the surface) were used for electrochemical evaluation (n=4). Sixteen-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated (air + 10% CO₂) modified Tani-Zucchi synthetic saliva at 37°C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N₂ + 10% CO₂) two hours before and during testing. Polarization resistance (R_p), Tafel slopes and passivation current density (I_pass) were determined. Corrosion current density (I_corr) was calculated for each specimen. Cast pure Ti, commercially pure Ti (CPTi) and Ti-6Al-4V were used as controls. Numerical results were statistically analyzed by nonparametric methods (a=0.05). Results: OCP measurements showed that all the alloys stabilized after the 16-hour immersion. On the anodic polarization diagram, a reduced passivation range compared to that of CPTi was seen in all the alloys. The Kruskal-Wallis test showed significant differences among all metals tested for OCP, R_p, and I_pass (p<0.05). The R_p and I_pass of Ti-6Al-4V tended to be lower and higher values compared to that of others, respectively. Conclusion: The results from the present study showed those the Ti-Al and Ti-Al-Cu alloys in the present composition ranges have acceptable corrosion resistance within the intraoral potentials. This study was partially funded by NIH/NIDCR grant DE 11787.