Electrochemical Behavior Assessment of Micro- and Nano-Grained Commercial Pure Titanium in H 2 SO 4 Solutions
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JMEPEG DOI: 10.1007/s11665-016-2489-2
Electrochemical Behavior Assessment of Microand Nano-Grained Commercial Pure Titanium in H2SO4 Solutions Arash Fattah-alhosseini, Ali Reza Ansari, Yousef Mazaheri, and Mohsen Karimi (Submitted June 29, 2016; in revised form September 29, 2016) In this study, the electrochemical behavior of commercial pure titanium with both coarse-grained (annealed sample with the average grain size of about 45 lm) and nano-grained microstructure was compared by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis. Nano-grained Ti, which typically has a grain size of about 90 nm, is successfully made by six-cycle accumulative roll-bonding process at room temperature. Potentiodynamic polarization plots and impedance measurements revealed that as a result of grain refinement, the passive behavior of the nano-grained sample was improved compared to that of annealed pure Ti in H2SO4 solutions. Mott-Schottky analysis indicated that the passive films behaved as n-type semiconductors in H2SO4 solutions and grain refinement did not change the semiconductor type of passive films. Also, Mott-Schottky analysis showed that the donor densities decreased as the grain size of the samples reduced. Finally, all electrochemical tests showed that the electrochemical behavior of the nano-grained sample was improved compared to that of annealed pure Ti, mainly due to the formation of thicker and less defective oxide film. Keywords
commercial pure titanium, electrochemical impedance spectroscopy, Mott-Schottky analysis, nano-grained
1. Introduction Over the last decade, improving the mechanical properties of metals and alloys via severe plastic deformation (SPD) processes has received increasing attention (Ref 1-3). SPD processes create huge plastic strains in materials, at relatively low temperatures (usually less than 0.4 Tm, where Tm is the melting temperature). They are used to create nano-grained (NG) and ultrafine-grained (UFG) metallic materials with grain size in the range of 101000 nm (Ref 4). Various SPD processes such as equal channel angular pressing (ECAP) (Ref 5), accumulative roll bonding (ARB) (Ref 6), and high-pressure torsion (Ref 7) have been developed and used for different metals and alloys. Among the titanium alloys, aerospace and biomedical applications make intensive use of the well-known Ti-6Al4 V alloy. Cost consideration and concerns regarding the corrosion resistance and toxicity of the elements vanadium and aluminum for human health constitute a strong motivation for the replacement of Ti-6Al-4 V (Ref 8). A viable candidate is the lower cost commercial pure Ti (ASTM grade 2), from which a better resistance against corrosion is expected, although its yield strength compares much lower than that of the Ti-6A-4 V, viz. 275 MPa against 850 MPa. Enhancement of commercial Arash Fattah-alhosseini, Ali Reza Ansari, and Yousef Mazaheri, Department of Materials Engineering, Bu-Ali Sina University, Hamadan 65178-38695, Iran; and Mohsen Karimi, Departme
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