Passive Film Degradation and Microbiologically Influenced Corrosion Mechanism of β Titanium Alloy Induced by Pseudomonas aeruginosa Biofilms

This study investigated microbiologically influenced corrosion (MIC) and passive-film degradation of a Ti-15Mo-3Al-2.7Nb-0.25Si β titanium alloy exposed to Pseudomonas aeruginosa. The alloy comprised a continuous β-Ti matrix with dispersed α-Ti precipitates, and this α/β dual-phase microstructure provided a potential microstructural basis for spatial variations in passivation behavior among different microregions. During immersion, P. aeruginosa formed a heterogeneous biofilm of bacterial cells and extracellular polymeric substances, altering interfacial mass transfer, oxygen distribution, and local chemistry. Relative to the sterile control, the inoculated group showed increases in maximum pit depth from 2.4 to 4.1 μm and corrosion current density from 8.72 to 17.2 nA cm−2, while the charge-transfer resistance decreased to 4.32 MΩ cm2 after 14 d, confirming enhanced localized corrosion. Mott-Schottky and XPS analyses showed that the donor density increased from 1.07 × 1019 to 1.29 × 1019 cm−3 and the Ti4+ fraction decreased from 72.29% to 66.74% and the relative Ti0 fraction increased from 7.01% to 17.59%, reflecting increased defect accumulation within the film, impaired passive-film integrity, and reduced local protective capability. P. aeruginosa therefore increases the MIC susceptibility of this β titanium alloy by biofilm-induced interfacial microenvironmental heterogeneity. These findings support MIC assessment and integrated antifouling-anticorrosion surface design for marine β titanium alloys.