Corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo alloy in artificial seawater with various fluoride concentrations and pH values

Herein, we systematically investigate the corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in artificial seawater with various fluoride ion (F−) concentrations and pH values using electrochemical, static immersion measurements and surface characterizations. Results of electrochemical tests manifest that increasing the F− concentration and/or reducing pH value can deteriorate the corrosion performance of Ti80 alloy due to the dissolution of the compact passive film into the porous passive film. Besides, the electrochemical parameters obtained from polarization curves indicate that the F− concentration has few effects on the cathodic reaction but noticeable promoting effects on the anodic process, whereas the increase of pH plays a significant role in inhibiting both cathodic and anodic processes. In addition, surface characterizations reveal the preferential dissolution of the equiaxed α phase compared to the intergranular β phase, resulting from its relatively low Volta potential. We also interpret the F− concentrations and pH values dependent corrosion behaviour based on the mixed potential theory and illustrate the corrosion mechanisms associated with F− in artificial seawater. We believe that the insights into the F− concentration and pH value dependent corrosion behaviour can provide practical guidelines for the design and development of Ti alloys with high-corrosion resistance.