Corrosion behaviour of Ti–Ta–Sn alloy systems in 0.9% NaCl solution

Two alloys of varying contents of tantalum (Ta) and tin (Sn) were prepared and homogenized to evaluate their microstructural and electrochemical characteristics. The microstructural features were revealed through optical microscopy and X-ray diffraction methods. The formation and stability of passive film was studied by open circuit potential, potentiodynamic polarization and electrochemical scratch tests. The electrochemical impedance spectroscopy results simulated with equivalent electrical circuit suggested bilayer structure of outer porous and inner barrier oxide films. The quantitative data showed thick inner barrier oxide film retarded electrochemical reactions at low Ta and Sn concentration. The increased percentage of Ta and Sn deteriorated barrier properties by agglomeration of Ta2Sn3 and Ta0.15Ti0.85 precipitates within grains and at the grain boundaries.