Lara Rodríguez, Laura M.

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    Electrochemical characterization of plasma electrolytic oxidation coatings on TiAI and Ti6AI4V for biomedical applications
    (2010) Lara Rodríguez, Laura M.; Sundaram, Paul A.; College of Engineering; Caceres, Pablo; Quintero, Pedro; Department of Mechanical Engineering; Colucci, José
    The titanium alloys presently used for hard tissue replacement and other biomedical applications meet the principal requirements to perform with adequate host response in the body environment. However, some concern related to their corrosion properties and the release of metal ions in the body has triggered research towards new and efficient methods to overcome these problems. Simultaneously, the challenge lies in the development of multifunctional surfaces that mimic their host tissues in an attempt to enhance biocompatibility of the substrate material by promoting a stable implant/tissue interface. The present research explores the newly developed technique of plasma electrolytic oxidation (PEO) to modify the functional surfaces of gamma titanium aluminide (γTiAl) and Ti6Al4V alloys with the ultimate goal of using these materials in hard tissue, biomedical applications. The effectiveness of these surface treatments on the corrosion performance of the alloys was studied and compared using analytical imaging techniques such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and corrosion testing through Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS). Although γ TiAl has been used mainly in aerospace applications, previous studies have suggested the potential of this alloy for hard tissue replacement. Additionally, the growing need for new titanium alloys with better corrosion properties and without the toxic effects of vanadium motivates the current research. A significant relationship was found between the coating characteristics and the voltagecurrent conditions applied during the plasma electrolysis process. Highly porous surfaces (average pore size up to 500nm and 3.7µm in γTiAl and Ti6Al4V respectively), uniform and thick coatings were produced on the surfaces of both alloys. Features such as composition, morphology and topography were found to be alloy specific. Electrochemical tests using simulated body fluid (SBF) solutions highlighted the differences in corrosion behavior of the alloys with and without the PEO surface treatment. Although γTiAl exhibited an increased susceptibility to localized corrosion, surface modification with the PEO coatings demonstrated a noticeable reduction of this corrosion mechanism. Quantitatively, corrosion rate (icorr) reduction of about 90% and 78% were estimated under particular conditions of the coatings applied on γTiAl and Ti6Al4V. Moreover, results obtained by EIS suggested the improvement of corrosion resistance of the PEO treated alloys by increased polarization resistance values (as much as to thirty and four times the values obtained for untreated specimens). EIS technique allowed elucidating the interactions between the Ca-P rich coating and the simulated body fluid (SBF).