Passive and electrochemical response of friction stir processed pure Titanium

In the present work, the effects of multi-pass friction stir processing on the passive behavior and electrochemical response of pure Titanium in a phosphate buffer solution (pH = 10.69) were studied. Microstructures 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, finer microstructure 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 refinement induced by friction stir processing. Moreover, Mott–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. [Display omitted] •FSP decreased the grain size down to submicron range, thanks to dynamic recrystallization phenomena.•Grain refinement led to a reduction in both corrosion and passive current densities.•FSP promoted formation of much more resistive and thicker protective passive films.•FSP treatments lowered the donor densities on all levels.•Multi-pass FSP seems to be of great potential for increasing the corrosion resistance of pure Ti.