Effect of friction stir surface processing on the corrosion behavior of Ti-6Al-4V in Ringer's solution

In this study، the effect of friction stir surface processing on the corrosion behaviour of Ti-6Al-4V was investigated. The electrochemical corrosion properties were studied at 37°C in Ringer''s solution using open circuit potential، potentiodynamic polarisation and electrochemical impedance spectroscopy techniques. The potentiodynamic tests showed that Ti-6Al-4V exhibited spontaneous passivity before and after processing and passivity breakdown was not observed at potentials as high as 3 VSCE. However، the results indicated that the friction stir processing deteriorated the corrosion resistance of Ti-6Al-4V. The results of the impedance experiments were simulated by an equivalent circuit and a good agreement was achieved between experimental and simulated results. The circuit element values were obtained by ZView software. The EIS analysis indicated that the passive film formed on the processed specimen exhibited lower polarization resistance when compared to the base metal (by more than 2 orders of magnitude). Furthermore، potentiodynamic polarization tests showed that the corrosion current density of friction stir processed sample increased by more than 2 orders of magnitude. The inferior corrosion resistance was attributed to the microstructure changes and alloying elements heterogeneity due to friction stir processing.