The Estimation of Corrosion Behavior of NiTi and NiTiNb Alloys Using Dynamic Electrochemical Impedance Spectroscopy

Linear anodic potentiodynamic polarization and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out for NiTi and NiTiNb alloys in physiological 0.9 wt% NaCl solution in order to assess their corrosion resistance. DEIS measurements were performed from open circuit potential to dissolution potential. It was shown that the impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure. The impedance spectra of various potential regions were fitted and also discussed. The surface morphology of the alloys after linear anodic polarization test was studied using scanning electron microscopy (SEM) technique

Electrochemical characterization of ZrTi alloys for biomedical applications. Part 2. The effect of thermal oxidation

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

Multiscale electrochemical investigation of the corrosion resistance of various alloys used in dental prostheses

The electrochemical behaviour of Ag-Pd (Paliag), Ni-Cr (Heraenium NA), and Co-Cr (Heraenium CE) alloys used in dental prosthetics construction of crowns and bridges was studied in 0.9% NaCl solution at 25 ºC. The localized electrochemical characteristics related to corrosion resistance and eventual breakdown of the protecting oxide layers were investigated by scanning electrochemical microscopy (SECM), whereas potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed to establish oxide stability. When the corrosion resistance of the alloys was evaluated by means of the corrosion current value determined around their corresponding open circuit potential in 0.9% NaCl solution, good protection can be expected resulting from their spontaneous passivation (low current densities in the order of tenths of μA cm-2). The polarization resistance of all the samples increased with immersion time, in the sequence Ag-Pd < Heraenium NA < Heraenium CE. Yet, increased electrochemical activity was detected with SECM when the alloys were polarized at +0.40 VSCE, a value that may be eventually experienced in the human body. Though a passivation mechanism was still operating in the chromium-containing alloys, oxide dissolution and precipitation of corrosion products occurred on Ag-Pd instea

Evaluation of the corrosion resistance of plasma nitrided austenitic stainless steel

Plasma nitriding at 500 °C for 14 h was applied to austenitic 304 stainless steel for surface hardening. The effect of surface treatment on the corrosion resistance of the material was investigated in naturally-aerated 0.5 M NaCl solution for 30 days using linear potentiodynamic polarization and electrochemical impedance spectroscopy methods. Both as-cast and plasma nitrided stainless steel samples underwent spontaneous passivation, though the nitrided sample exhibited more positive zero current potential, higher breakdown potential, and lower anodic current densities than the as-cast material. Impedance spectra were interpreted in terms of a duplex passive film, corrosion resistance mainly arising from a thin inner compact layer, whereas the outer layer was more porous and less sealing. Capacitive behaviour and high corrosion resistance were observed in the low and medium frequency ranges for the nitrided sample

Electrochemical characterization of ZrTi alloys for biomedical applications

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 0C, 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 corrosio

Investigation of processing effects on the corrosion resistance of Ti20Mo alloy in saline solutions

The electrochemical properties of Ti20Mo alloys prepared using different fabrication procedures, namely cold crucible levitation melting (CCLM) and powder sintering, were investigated using linear potentiodynamic polarization and EIS measurements. The surface condition was established using AFM, with the observation of a more porous surface finish in the case of powder sintering. A major effect of surface conditioning on the corrosion resistance of Ti20Mo alloys was observed, where the compact finish exhibits a superior corrosion resistance in chloride-containing saline solutions. Less insulating surfaces towards electron exchange resulted for the more porous finish as revealed by scanning electrochemical microscopy (SECM

Electrochemical behaviour of ZrTi alloys in artificial physiological solution simulating in vitro inflammatory conditions

ZrTi alloys in artificial physiological solution simulating in vitro inflammatory conditions were investigated for biomedical application. Effect of surface treatment on the corrosion resistance of Zr5Ti, Zr25Ti, and Zr45Ti in acidified Ringer’s solution (pH = 3) at 25 ºC was evaluated using electrochemical impedance spectroscopy, potentiodynamic polarization curves, and scanning electrochemical microscopy. Thermal oxidation in air at 500 ºC produces materials with high in vitro corrosion resistance to acidic environments. Higher impedance values related to passivity were observed for oxidized ZrTi alloys compared to as-cast materials. SECM reveals thermal oxidation produced more compact and electrically insulating oxide filmsZirconium-titanium alloysBiomaterialsSurface treatmentSimulated physiological solutionElectrochemical techniquesCorrosion resistanc

Investigation of the electrochemical behaviour of TiMo alloys in simulated physiological solutions

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 microscop

Electrochemical characterization of pulsed layer deposited hydroxyapatite zirconia layers on Ti-21Nb-15Ta-6Zr alloy for biomedical application

A new titanium base Ti-21Nb-15Ta-6Zr alloy covered with hydroxyapatite-zirconia (HA-ZrO2) by pulsed laser deposition (PLD) technique was characterized regarding its corrosion resistance in simulated physiological Ringer’s solution at 37 °C. For the sake of comparison, Ti-6Al-4V standard implant alloy, with and without hydroxyapatite-zirconia coating, was also characterized. Multiscale electrochemical analysis using both conventional averaging electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization, and spatially-resolved microelectrochemical techniques (scanning electrochemical microscopy, SECM) were used to investigate the electrochemical behaviour of the materials. In addition, scanning electron microscopy evidenced that no relevant surface morphology changes occurred on the materials upon immersion in the simulated physiological solution, despite variations in their electrochemical behaviour. Although uncoated metals appear to show better performances during conventional corrosion tests, the response is still quite similar for the HA–ZrO2 coated materials while providing superior resistance towards electron transfer due to the formation of a more dense film on the surface, thus effectively behaving as a passive material. It is believed corrosion of the HA–ZrO2 coated Ti-21Nb-15Ta-6Zr alloy will have negligible effect upon biochemical and cellular events at the bone-implant interface and could facilitate osseointegratio