Corrosion Response of Co-6Ti-11V-9Cr Alloy in Acidic Chloride Solutions

The corrosion response of a Co-6Ti-11V-9Cr superalloy was investigated in 0.05 mol/L H2SO4 containing 0, 0.01, 0.1 or 0.5 mol/L NaCl. Open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation, scanning electron microscopy (SEM) and electrochemical noise (EN) analysis were combined to determine how chloride concentration affects passive-film stability and localised corrosion. Increasing the NaCl concentration shifted both the OCP and corrosion potential in the negative direction. The fitted resistance of the barrier layer decreased from 4.61 × 104 to 0.39 × 104 Ω cm2, whereas the passive current density increased from 4.58 × 10−6 to 1.78 × 10−5 A cm−2. SEM and EN analyses further showed that chloride enrichment promoted local passive-film breakdown, changing the surface response from relatively uniform corrosion to localised attack and pitting. These findings provide an experimental basis for assessing Co-Ti-V-based superalloys in acidic chloride-containing service environments.