Characteristics of Passive Films Formed on As-Cast Ti–6Al-4V in Hank’s Solution Before and After Transpassivation

Abstract

In this work, the characteristics of passive films formed on as-cast Ti-6Al-4V before and after transpassivation by electrochemical methods will be studied. A simulated body fluid of Hank’s solution was used as the electrolyte in this work. According to the potentiodynamic polarization test, the passivation range, transpassive range, and repassivation range of as-cast Ti-6Al-4V were obtained. Afterward, the potentiostatic polarization was employed to passivate the Ti-6Al-4V in both passivation and repassivation ranges. Electrochemical impedance spectroscopy (EIS) was used to analyze the characteristics of formed passive films. Different electrochemical behavior of as-cast Ti–6Al-4V is found in passivation and repassivation ranges. The passivation current density of the sample in the repassivation range is significantly larger than that in the passivation range. Meanwhile, the growth rate of passive film in the repassivation range is also greater than that in the passivation range. Although the sample shows a higher charge transfer impedance in the repassivation range, metastable pitting corrosion is also observed, indicating the formation of the unstable passive film. Such results advance the understanding of as-cast Ti-6Al-4V polarized under different potentials for potential biomedical applications.

In vitro tribocorrosion evaluation of carbide-derived carbon (CDC) for hip implants

“…The applied anodic potential (500 mV) is considered a corrosion-accelerated condition [28,34,48], which can explain the fact that Ti-E ano showed the highest Kc among all potentials. However, 500 mV is in the range of the repassivation potential for Ti6Al4V [30], and it was reported that the thickness of the passive film created on Ti alloys is proportional to the applied potential [49–52], meaning that the regrowth of the passive layer is encouraged under anodic conditions, which can be supported by the high oxygen concentration from EDS. As shown in Figure 10, the passive layer was on the Ti6Al4V before testing (Figure 10(i)), and it was removed by the alumina pin under sliding (Figure 10(ii)), where the wear debris accumulated around the wear scar and in the grooves to form three-body mechanism as can be observed from SEM images (Figure 7(a)).…”