Electrochemical characterization of cast Ti–Hf binary alloys

Abstract

This study characterized the electrochemical behavior of Ti–Hf binary alloys in a simulated oral environment. Ti–Hf alloys (10, 20, 25, 30, 35 and 40 mass% Hf) were prepared by arc-melting titanium sponge and hafnium sponge. Specimens of each alloy ( n = 4) were prepared using a dental titanium casting system with a MgO-based investment. Specimens were inspected with X-ray radiography to ensure minimal internal porosity. Castings ( n = 4) made from pure titanium and commercially pure titanium were used as controls. The ground flat surface (10 mm × 10 mm) on each specimen where approximately 30 μm was removed was used for the characterization. Sixteen-hour open-circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed sequentially in aerated (air + 10% CO 2) MTZ synthetic saliva at 37 °C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N 2 + 10% CO 2) 2 h before and during testing. Polarization resistance ( R P) and Tafel slopes were determined, as were corrosion current density ( I CORR) and passive current density ( I PASS). Results were subjected to nonparametric statistical analysis ( α = 0.05). The OCP stabilized (mean values −229 mV to −470 mV vs. SCE) for all specimens after the 16-h immersion. Similar passivation was observed for all the metals on their anodic polarization diagrams. The Kruskal–Wallis test showed significant differences in OCP among the test groups ( p = 0.006). No significant differences were found in R P, I CORR or I PASS among all the metals ( p > 0.3). Results indicate that the electrochemical behavior of the Ti–Hf alloys examined resembles that of pure titanium.