Effects of Mo addition on the mechanical properties and Cl− corrosion behavior of TA18 titanium alloy: Experimental and DFT computational study

The dual challenge of achieving high structural strength and maintaining resistance to chloride-induced degradation has limited the wider application of TA18 (Ti–3Al–2.5 V) titanium alloy in deep-sea environments. This study systematically investigates the corrosion behavior and mechanisms of TA18–xMo (x = 0, 2, 4, 6, and 8 wt%) alloys experimentally in chloride-rich environments, while density functional theory (DFT) calculations were performed on ideal vacuum surfaces to elucidate the intrinsic electronic effects of Mo addition on the work function and surface electronic structure. The TA18–6Mo alloy exhibited optimal mechanical properties, with a compressive yield strength of 1112 MPa and an ultimate compressive strength of 1611 MPa—nearly double those of the base TA18 alloy. Corrosion resistance increased steadily with Mo content. At 8 wt% Mo, the corrosion current density decreased by ∼70 % relative to TA18, while the passive film resistance ( R p ) reached 2.375 × 10 6 Ω cm 2 , over ten times higher than that of the base alloy. DFT calculations revealed that Mo addition raises the work function, thereby suppressing anodic dissolution. After 5 days of immersion in 5 mol/L HCl, the TA18–8Mo alloy exhibited only 30 % of the mass loss observed for TA18. XPS analysis confirmed the formation of a dense TiO 2 –MoO 3 composite passive film on the alloy surface. These findings demonstrate that single-element Mo alloying provides a simple and effective strategy to enhance both strength and corrosion resistance of TA18, while the established quantitative link between work function and corrosion behavior offers new theoretical guidance for designing high-performance titanium alloys for deep-sea applications.