Corrosion Characteristics of Cast Ti-Cu Binary Alloys

Objective: This study characterized the corrosion behavior of a series of binary Ti-Cu alloys (1, 2, 3, 5, 7, and 10 mass% Cu) in a simulated oral environment. Methods: Ti-Cu alloys were prepared by arc-melting titanium sponge (>99.97%, TST-1, Toho Titanium, Japan) and oxygen-free high conductivity (OFHC) copper (99.95%, Goodfellow Cambridge Ltd., England). Wax patterns (10mm x 10mm x 2mm) were invested into a MgO-based investment and cast in a centrifugal casting machine (Ticast Super R, Selec Co., Japan) (n=4). X-ray diffractometry was carried out for all the metals tested. Pure titanium (from titanium sponge), commercially pure titanium (CP Ti; ASTM grade 2, Titanium Industries, USA), and Ti-6Al-4V (ASTM grade 5, Titanium Industries) served as controls. Sixteen-hour open circuit potential (OCP) measurements, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air+10%CO₂) modified Tani-Zucchi synthetic saliva at 37ºC. Potentiodynamic anodic polarization was conducted in the same medium deaerated (N₂+10%CO₂) two hours before and during testing. Polarization resistance (R_p), Tafel slopes, corrosion current density (I_corr), and passive current density at 500 mV (I_pass) were determined. The experimental results were statistically analyzed by non-parametric methods (a=0.05). Results: X-ray diffraction revealed the presence of Ti₂Cu in the experimental alloys containing more than 3% Cu. The OCP did not completely stabilize in most of the experimental specimens. Passive regions occurred for all the metals on their anodic polarization diagrams, and no breakdowns were observed. The Kruskal-Wallis test showed significant differences among all the metals tested for OCP, R_p, and I_pass (p<0.02). The metals with more than 7% Cu significantly decreased R_p compared with that of pure Ti and CP Ti (p<0.03). Conclusion: Alloying with up to 5% Cu did not significantly reduce the corrosion resistance of pure titanium. Partially funded by NIH/NIDCR grant DE 11787.