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Title: Structural and Mechanical Characteristics of Anodic Oxide Films on Titanium

Abstract

Oxide films were grown electrochemically on polycrystalline titanium in 0.1 M sulfuric acid (H2SO4) from open-circuit potential to a final potential of 9.4 V (vs silver-silver chloride [Ag-AgCl]) using three anodization rates: a step polarization, growth at 200 mV/s, and growth at 1 mV/s. Anodic polarization curves showed various degrees of oxygen evolution above 5.4 VAg-AgCl, indicating that the extent of oxide film breakdown depends on film growth rate, with slower growth rates undergoing more severe film breakdown. In-situ characterization of mechanical behavior of oxide films by nanoindentation revealed that the oxide film can sustain a tensile stress up to 2.5 GPa prior to film fracture. Among these three anodization rates, the oxide film formed by step polarization exhibited the highest film-strengthening effect. At applied potentials prior to oxide film breakdown, all films exhibited a strength of ≈1 GPa. The films ranged from amorphous titanium dioxide (TiO2) to anatase, with the extent of crystallization increasing with decreasing film growth rate. Correlations between electrochemical polarization, structural characteristics, and the mechanical behavior of these anodic films are discussed in relationship to electrostrictive stresses, which may lead to the breakdown of passive films. KEY WORDS: anodic polarization, films, nanoindentation, titanium, transmission electron microscopy.

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
15010421
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Corrosion, 57(6):523-531; Journal Volume: 57; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANODIZATION; CRYSTALLIZATION; TITANIUM OXIDES; POLARIZATION; STRESSES; TITANIUM; MECHANICAL PROPERTIES; MORPHOLOGY; Environmental Molecular Sciences Laboratory

Citation Formats

Pang, Mengzhi, Eakins, Daniel E, Norton, Murray G, and Bahr, David F. Structural and Mechanical Characteristics of Anodic Oxide Films on Titanium. United States: N. p., 2001. Web. doi:10.5006/1.3290378.
Pang, Mengzhi, Eakins, Daniel E, Norton, Murray G, & Bahr, David F. Structural and Mechanical Characteristics of Anodic Oxide Films on Titanium. United States. doi:10.5006/1.3290378.
Pang, Mengzhi, Eakins, Daniel E, Norton, Murray G, and Bahr, David F. Mon . "Structural and Mechanical Characteristics of Anodic Oxide Films on Titanium". United States. doi:10.5006/1.3290378.
@article{osti_15010421,
title = {Structural and Mechanical Characteristics of Anodic Oxide Films on Titanium},
author = {Pang, Mengzhi and Eakins, Daniel E and Norton, Murray G and Bahr, David F},
abstractNote = {Oxide films were grown electrochemically on polycrystalline titanium in 0.1 M sulfuric acid (H2SO4) from open-circuit potential to a final potential of 9.4 V (vs silver-silver chloride [Ag-AgCl]) using three anodization rates: a step polarization, growth at 200 mV/s, and growth at 1 mV/s. Anodic polarization curves showed various degrees of oxygen evolution above 5.4 VAg-AgCl, indicating that the extent of oxide film breakdown depends on film growth rate, with slower growth rates undergoing more severe film breakdown. In-situ characterization of mechanical behavior of oxide films by nanoindentation revealed that the oxide film can sustain a tensile stress up to 2.5 GPa prior to film fracture. Among these three anodization rates, the oxide film formed by step polarization exhibited the highest film-strengthening effect. At applied potentials prior to oxide film breakdown, all films exhibited a strength of ≈1 GPa. The films ranged from amorphous titanium dioxide (TiO2) to anatase, with the extent of crystallization increasing with decreasing film growth rate. Correlations between electrochemical polarization, structural characteristics, and the mechanical behavior of these anodic films are discussed in relationship to electrostrictive stresses, which may lead to the breakdown of passive films. KEY WORDS: anodic polarization, films, nanoindentation, titanium, transmission electron microscopy.},
doi = {10.5006/1.3290378},
journal = {Corrosion, 57(6):523-531},
number = 6,
volume = 57,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2001},
month = {Mon Jan 01 00:00:00 EST 2001}
}
  • During passage of cathodic current, large and reversible changes in ellipsometric parameters are interpreted in terms of changes in absorption and/or refractive index of surface anodic oxide films on Nb and Ti without significant change in thickness. A model based on dissolution and ionization of deposited hydrogen satisfactorily accounts for the slow reversible change in the optical absorption of films on Nb and for the impedance changes previously reported. More rapidly reversible changes in both absorption and refractive index occur in films on Ti. The decrease in refractive index is consistent with the reversible formation of TiOOH at negative potentials.more » 11 figures, 2 tables.« less
  • Ellipsometric and electrochemical techniques are used to study the anodic oxidation of titanium in aqueous and non-aqueous electrolytes. Transparent oxide films with a refractive index of 2.48 grown on electro polished surfaces exhibit ideal valve-metal behavior up to a thickness of approximately 30 nm. Beyond this thickness the refractive index and low-frequency dielectric constant of the film both decrease, but thicknesses of 100 nm can be achieved prior to complete breakdown under suitable experimental conditions. Open-circuit transients are used to determine the relation between the current density and the electric field in the oxide film.
  • Different aspects of the breakdown phenomena observed during the growth of anodic films on zirconium metal in aqueous solutions have been investigated. Two different mechanisms of breakdown are suggested as a result of the experimental observations. A mechanical breakdown, which is dependent upon the logarithm of the anodizing current density, has been observed in carbonate and sulfate solutions at low concentrations of salt or aci and/or low anodizing current densities. The appearance of small fissures in the ZrO/sub 2/ films is related to this type o breakdown. An electrical breakdown was observed in sulfamic acid solutions as well as inmore » sulfate and carbonate solutions as high salt or acid concentrations and/or high current densities. In the case of electrical breakdown, the first spark voltage showed a significant dependence upon the value of current density only in carbonate and sulfate anion containing solutions. A possible explanation for this dependence is suggested in agreement with Christov's model, taking into account also the incorporation of anions into the films. The different influences of the electrolytic solutions upon both types of breakdown are presented and discussed.« less