The effects of local sever plastic deformation through multi-pass friction stir processing on the passive and electrochemical response of pure Ti are studied in a borate buffer solution (pH = 7) in the present paper. Microstructures of treated and untreated samples were characterized using scanning electron microscopy. Results show that with increasing the number of friction stir processing passes, grains became finer in size. Electrochemical tests, including potentiodynamic polarization measurements and electrochemical impedance spectroscopy, showed that the friction stir processed sample provides superior passive behavior with highest corrosion resistance among all samples in the borate buffer solution. These improvements can be attributed to the emergence of diverse structural defects and grain refinement induced by friction stir processing operation. Moreover, Mott–Schottky analysis was performed to assess the semiconducting properties of passive films. It was found that the semiconducting behavior remained the same upon friction stir processing operation but reduced donor densities and provided an additional donor level.
