Investigation of pitting resistance of titanium based on a modified point defect model

The pitting resistance of titanium was studied under potential control in solutions containing chloride ions. The results evidenced that Cl− concentration had an effect on the metastable pitting intensity, but no significant influence on the uniform corrosion. XPS characterization revealed that some Cl− ions were present in the outer hydroxide layer, but few in the inner oxide layer, indicating that the inner oxide layer was impervious to Cl− ions. A cation–anion-vacancy condensation mechanism was considered for pit initiation based on the point defect model (PDM). The experimental results analyzed by the charge integration technique were in agreement with the derived relations.

Research highlights
► Split the metastable pitting current transients from the uniform corrosion current.
► Determine the oxide ionic properties and the penetration possibility of chloride ions.
► Modify the point defect model to explain pit initiation on titanium.
► Correlate the pitting potential to the metastable pit density.