The Influence of Cold Plastic Deformation on Passivity of Ti-6Al-4V Alloy Studied by Electrochemical and Local Probing Techniques

The influence of cold plastic deformation on passivity of Ti-6Al-4V alloy (UNS R56400) was investigated by means of potentiodynamic polarization, Mott-Schottky analysis, atomic force microscopy, and scanning Kelvin probe force microscopy. The results showed that the cold working increased the passive current density. Mott-Schottky analysis revealed the n-type semiconducting behavior of the passive film. The donor density of the passive film was declined by increasing the film formation potential. On the other hand, work hardening increased the density of defects within the passive film, regardless of the applied potential. The Volta potential maps showed that α phase possesses lower surface potential compared to the β, i.e., 38.6 mV. The plastic deformation decreased the surface potential of both phases; however, the relative nobility of the constituent phases had been slightly affected by cold working, i.e., 5 mV. The topographic results after immersion of the alloy in an aggressive acidic environment revealed that the Volta potential difference between α and β was sufficient to make α more vulnerable to corrosion attacks.