Simultaneous improvement of strength and corrosion resistance in β-type Ti-24Nb-4Zr-8Sn alloy through a spinodally modulated dual-phase microstructure

The growing demand for load-bearing components operating in chloride-containing environments calls for high-strength titanium alloys with enhanced corrosion resistance. In β-Ti alloys, conventional strengthening by discrete second-phase precipitation often introduces sharp compositional and electrochemical discontinuities at precipitate/matrix interfaces, promoting micro-galvanic corrosion and destabilizing passive films. Here we show that this trade-off between strength and corrosion resistance can be mitigated in Ti-24Nb-4Zr-8Sn (wt.%) by exploiting aging-induced spinodal decomposition, which produces a compositionally modulated and spatially continuous β/α" dual-phase microstructure with a characteristic wavelength of about 20 nm. This continuous modulation provides densely spaced barriers to dislocation glide and increases strength, while avoiding the sharp interfacial electrochemical contrast associated with conventional precipitate-strengthened microstructures. In addition, spinodal decomposition induces periodic compositional modulation within the β/α" microstructure, affecting passivation behavior through coupled Ti-O and Nb partitioning. The nanoscale α" domains are enriched in both Ti and O, providing favorable local chemical environments that can facilitate Ti-oxide formation and promote passivation. Concurrent nanoscale Nb modulation is associated with a greater relative contribution of Nb oxides to the passive film, helping stabilize the barrier layer. These effects contribute to a thicker, more laterally continuous, and less defective passive film, thereby reducing defect-assisted transport and improving corrosion resistance in chloride-containing media. Our findings highlight spinodal decomposition as a viable route to co-optimize strength and corrosion resistance in β-Ti alloys. © 2026 Acta Materialia Inc.