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The electrochemical behaviour of three ZrTi alloys (Zr5Ti, Zr25Ti and Zr45Ti) in Ringer's solution has been investigated. Their resistance against localized corrosion has been determined from cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy (EIS) measurements, whereas scanning electrochemical microscopy (SECM) was applied to investigate the local reactivity of the passive films developed on the materials, and scanning electron microscopy (SEM) was employed to characterize the surface morphology of the alloys subjected to anodic polarization. An increased reactivity could be detected with SECM when the metal samples were polarized at +0.50 VSHE, though the extent of this feature greatly depended on the nature of the metallic material. At 37 0 C, the Zr5Ti alloy was susceptible to localized corrosion. Though Zr25Ti alloy presented rather low pitting potential, the spontaneous corrosion potential of the material was sufficiently negative to require overpotentials around 600 mV for breakdown to occur. Finally, the Zr45Ti alloy exhibited a larger passive range in the polarization curve, and it was resistant to localized corrosion.

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This paper addresses on the electrochemical behaviour of three TiMo alloys exposed to simulated physiological environments. Their stability and corrosion resistance was characterized in order to explore the potential application for the manufacturing of implant materials. Ringer's solution together with an acidic modification of the Ringer's solution (pH = 3.1) at room temperature were considered. Both electrochemical methods (namely, potentiodynamic polarization curves and electrochemical impedance spectroscopy, EIS), and spatially-resolved scanning electrochemical microscopy (SECM), were used. Additionally, surface characterization was made employing optical microscopy and scanning electron microscopy (SEM). The oxide films formed on the TiMo alloys in neutral and acidic Ringer's solutions effectively protect the metal from dissolution in this environment, and no breakdown of the passive layer occurs in the potential range up to +1.00 V vs. SCE. SEM micrographs of retrieved samples do not show corrosion pits, cracks, or any other defects despite the rather high positive potential values reached during the potential excursion. EIS data reveal that two-layer oxide films are formed, consisting of a porous outer layer and a compact inner layer (approximately 5-6 nm thick), the latter accounting almost completely for the corrosion resistance of the materials. The corrosion resistance of the inner compact film towards metal dissolution is smaller in the acidic environment, whereas it increases with higher Mo contents in the alloy. The passive oxide films exhibit dielectric characteristics towards charge transfer, and they are imaged as insulators by scanning electrochemical microscopy.

In the last decade, new titanium alloys have been developed in different areas of dentistry, such as Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, and Ti5Al2.5Fe. The aim of this study was to compare the Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, Ti5Al2.5Fe, and Ti6Al4V alloys with the commercial titanium, regarding the corrosion resistance in artificial saliva. In the electrochemical estimations the polarization data are converted into instantaneous corrosion rate values (I corr ). The passivation properties were comparable for the four alloys. The EIS spectra are best fitted using an equivalent circuit (EC), which corresponds to the model of a two-layer structure for the passive film. High impedance values (in the order of 10 6 V cm 2 ) were obtained from medium to low frequencies for all materials suggesting high corrosion resistance in artificial saliva.The electrochemical and corrosion behavior of Ti6Al4V is not affected on substituting vanadium with niobium, iron, molybdenum, and tantalum.

Titanium alloys are used in odontology applications owing to their excellent biocompatibility. The corrosion resistance of titanium alloys is an important component of their biocompatibility. In this study, the electrochemical corrosion resistance of Ti6Al4V, Ti6Al7Nb, Ti6Al2Nb1Ta1Mo, Ti5Al2,5Fe and commercial titanium in Afnor saliva was investigated. Maintaining titanium and Ti6Al7Nb alloy in Afnor saliva for 7 days results in the formation of a protective layer, the resistance of which is high and could be comparedwith that of a passive layer resulting from electrochemical treatment. The replacement of vanadium with niobium or iron favours the passivation, thus increasing the corrosion resistance.

Oxidation in air of ZrTi alloys at 500 ºC for 2 h produces oxide-covered materials with a very high corrosion resistance in Ringer's solution at 37 ºC. The oxide layers present a double-layer structure, comprised by a thin and very compact inner layer of ca. 5 nm thickness, and a less compact, more porous and thicker outer layer. The thickness of the outer layer greatly varies with the composition of the base ZrTi alloy, but has very little influence in the overall electrochemical behaviour of the material. The nature of the oxide layer is a mixture of ZrO2 and TiO2, and no evidence of higher oxidation states of the metal could be found using XRD data. Anodic dissolution through the passive layers formed on the oxidized alloys is greatly diminished compared to those measured from the untreated materials, allowing all the alloying ratios between Zr and Ti to be potentially considered for implant application. The combination of alloying with titanium and oxidation in air at 500 ºC resulted in the materials that do not exhibit the characteristic susceptibility of zirconium towards the initiation of localized corrosion processes in aqueous chloride-containing electrolytes even for anodic polarizations up to +1.00 VSCE, a value well above the highest polarization experienced in the human body. Though all the oxidized alloys exhibited remarkable corrosion resistances, the best behaviour was found for oxidized Zr45Ti.