Microbiologically influenced corrosion of titanium alloys with distinct phase microstructures by sulfate-reducing bacteria in seawater.

The corrosion resistance of titanium alloys in marine environments can be compromised by sulfate-reducing bacteria (SRB), yet it remains unclear whether alloy design principles established in abiotic media remain applicable under microbiologically active conditions. This study investigated the microbiologically influenced corrosion (MIC) behavior of three titanium alloys with different phase constitutions and alloy chemistries: β-type Ti-18Mo, α + β-type Ti-62A, and α-type Ti-6Al, following exposure to Desulfovibrio desulfuricans. A clear resistance hierarchy was observed: Ti-18Mo > Ti-62A > Ti-6Al. The results indicate that this hierarchy arises from the coupled effects of phase constitution, alloying chemistry, and passive-film stability. Sulfide-associated surface species detected after SRB exposure were accompanied by pronounced changes in passive-film chemistry, consistent with sulfide-associated modification of the passive film. Ti-18Mo exhibited the highest resistance, together with a comparatively greater TiO2-related contribution after prolonged Ar+ sputtering and the lowest donor density. These findings indicate that the observed MIC resistance is governed by the combined influence of microstructural characteristics and alloy-dependent passive-film chemistry, highlighting both factors as important considerations in the design of titanium alloys for SRB-containing marine environments.