Electrochemical Reaction of Cast Experimental Ti-Al and Ti-Al-Cu Alloys

Objective: This study characterized the electrochemical behavior of experimental Ti-5.0mass%Al and Ti-5Al-Cu (1, 3 or 5.0%Cu) alloys. Methods: Alloys were made by melting together titanium sponge (>99.7%, TST-1, Toho Titanium, Japan) and the alloying constituents (Al 99.999%, or Cu 99.95%, Goodfellow Corp., USA) in an argon arc furnace (Mark III, IVI Corp., USA). The alloy specimens (10mm x 10mm x 2mm; n=4) were cast using a centrifugal casting machine (Ticast Super R, Selec, Japan) with MgO-based investment (Selevest CB, Selec). After polishing down approximately 30 µm, 16-hour open circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed in an aerated (air+10%CO₂) modified Tani-Zucchi saliva at 37°C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N₂+10%CO₂). Polarization resistance (R_p), Tafel slopes and passivation current density (I_pass) were determined over the potential of approximately 1800 mV. Corrosion current density (I_corr) was calculated. Cast pure titanium made from titanium sponge, commercially pure titanium (CPTi; ASTM grade 2) and Ti-6Al-4V (64; ASTM grade 5) were used as controls. The concentrations of elements released from the electrolyte during corrosion testing were determined using an ICP-MS (ELAN DRC II, Perkin-Elmer Inst., USA). Results were statistically analyzed using non-parametric methods (corrosion) and one-way ANOVA (dissolution) (α=0.05). Results: All the experimental alloys stabilized during the OCP measurements and passivated during the anodic polarization. The Kruskal-Wallis test indicated significant differences among all metals tested for OCP, R_p and I_pass (p<0.038). The experimental alloys had significantly better corrosion characteristics compared to Ti-6Al-4V (p<0.025). Trace amounts of Cu (0.99-3.10µg) were detected in the electrolyte of Ti-5Al-Cu. Conclusion: These results showed that the corrosion resistance of the experimental Ti-Al and Ti-Al-Cu alloys is similar to CP Ti within intraoral potentials. Partially funded by NIH/NIDCR grant DE11787.