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

Objective: This study characterized the corrosion behavior of binary Ti-Cr (7, 13, and 19 mass% Cr) alloys and ternary Ti-Cr-Cu alloys (3% Cu alloyed to each binary alloy). Methods: 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=3). 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 ASTM grade 2 CP titanium was examined as the control. 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 CP titanium was seen on all the alloys. Among all the experimental alloys, larger passivation potential ranges were observed on the Ti-7%Cr and Ti-7%Cr-3%Cu alloys. The Kruskal-Wallis test showed significant differences among all metals tested for R_p, I_corr, and I_pass. The Mann-Whitney test showed significantly lower R_p and higher I_corr values for all the alloys compared to CP titanium. Conclusion: The results from the present study showed that these experimental Ti-Cr and Ti-Cr-Cu alloys have acceptable corrosion resistance within the intraoral potentials. This study was partially funded by NIH/NIDCR grant DE 11787.