In the present work, the effects of multi-pass friction stir processing on the passive behavior and elec- trochemical response of pure Titanium in a phosphate buffer solution (pH ¼ 10.69) were studied. Mi- crostructures of treated and untreated samples were characterized using scanning electron microscopy. Results showed that with increasing the number of passes of the friction stir process, fi ner micro- structure was obtained. Electrochemical tests, including potentiodynamic polarization measurements and electrochemical impedance spectroscopy, showed that the friction stir processed sample provided a superior passive behavior with highest corrosion resistance among all samples in the phosphate buffer solution. These enhancements can be ascribed to the development of the various defects in the structural and grain re fi nement induced by friction stir processing. Moreover, Mott e Schottky test was performed to assess the semiconducting properties of passive layers. It was found that the semiconducting behavior remained the same upon friction stir processing, but reduced the electron donor density and provided an additional donor level.
