In the present study, various electrochemical tests were used to investigate the passive and electrochemical response of annealed and nano-grained commercial pure Titanium in Ringer's physiological solution at 37 °C. Nano-grained pure Titanium, which typically has an average grain size of 90 ± 5 nm, was obtained by sixcycle accumulative roll bonding process. Polarization and electrochemical impedance spectroscopy plots illustrated that as a result of grain refinement process, the passive response of the nano-grained sample was improved compared to that of its coarse-grained counterpart in Ringer's physiological solution. Mott–Schottky analysis indicated that the passive films behaved as n-type semiconductors in Ringer's physiological solution and grain refinement did not change the conductivity type of the passive films. Additionally, Mott–Schottky analysis showed that the donor density decreased by grain size reduction. Finally, nano-grained sample appeared to be more suitable for implant applications, mainly due to the formation of thicker and less defective oxide film
