In Vitro Electrochemical Behavior of Aged Ti-6Al-4V Alloy: A Trial of the Point Defect Model

Abstract

This article deals with the electrochemical behavior of passive films that were formed on the surface of age hardened Ti-6Al-4 V alloy in Ringer’s physiological solution at 37 °C. The influence of age hardening at 740 °C for different ageing times up to 8 h on the microstructural features and electrochemical properties were characterized. To do so, the microstructural evolution was studied using X-ray diffraction technique, Vickers microhardness test and scanning electron microscopy, while the electrochemical characteristics were investigated by electrochemical impedance spectroscopy, Mott-Schottky analysis and point defect model (PDM). The experimental results indicated less microhardness and microstrain values due to proceeding phase transformation of β to α at prolonged ageing times, which exerted an adverse effect on the passive film properties as a result of the formation of more defective passive films upon the surface. The PDM results revealed that deteriorated corrosion protection ability of the passive films on the surface of overaged specimens can be attributed to higher diffusivity of the point defects in their respective crystal structure.