Investigation of passivation and galvanic corrosion of Ti-Nb alloys and pure titanium.

The aim of this study was to investigate the role of the passive layers in galvanic corrosion of Ti-Nb alloys and commercially pure titanium (cp-Ti). Ti-Nb alloys with 5, 10, 15, and 20 wt% niobium (Nb) content were prepared using an arc-melting technique under high purity Ar gas. The cp-Ti was used as a control. The electrochemical corrosion behaviors were investigated by A.C. impedance, potentiodynamic polarization, and galvanic corrosion tests. According to the results of impedance analysis, the passivation layer on Ti-Nb alloys consisted of outer, intermediate, inner, and metal defect layers, while the passivation layer on cp-Ti consisted of outer, intermediate, and inner layers. According to the results of anodic polarization tests, Ti-Nb alloys exhibited better zero potentials and reduced zero current densities. The outer layer and the inner layer of Ti-Nb alloys and cp-Ti had an effect mainly on the values of the initial galvanic current density and the sign of galvanic current density, respectively. Ti-10Nb alloy exhibited a relatively high initial galvanic current density compared to the other Ti-Nb alloys. Unlike Ti-5Nb, Ti-10Nb, and Ti-15Nb, which exhibited galvanic current densities with a minus sign, Ti-20Nb exhibited a galvanic current density with a plus sign due to its weaker inner layer than that of Ti. [ABSTRACT FROM AUTHOR]