Harnessing oxygen-driven phase engineering for a strong and ductile duplex titanium alloy

Overcoming the strength-ductility trade-off remains a daunting challenge for titanium (Ti) industry. Duplex (α + β) Ti alloys, represented by Ti-6Al-4 V, are the mainstay of Ti industry. However, the poor deformability of hexagonal close-packed (HCP) α phase, combined with semi-coherent α/β boundaries for strain incompatibility often cause limited elongation. Here, we propose an innovative strategy that harnesses O atoms with strong hardening ability in Ti alloys, as well as the rapid cooling and highly thermal gradients of laser powder bed fusion to construct a duplex Ti alloy, involving HCP Ti matrix embedded with O-rich nano-coherent face-centered cubic (NC-FCC) Ti. The duplex Ti-0.615 wt% O alloy achieves a high ultimate tensile strength of 1020 ± 4 MPa and an exceptional elongation of 21.8 ± 0.5%, together with a superior specific strength-ductility product of 4.93 GPa·%·cm3·g− 1. This unprecedented combination of mechanical properties originates from the O-rich NC-FCC, which promote dislocation slip transfer across the coherent phase boundaries (CPBs) and formation of extensive stacking faults near CPBs for enhanced strain compatibility. Additionally, the O-rich NC-FCCs strengthen the alloy via solid solution strengthening from O atoms. This work opens a promising avenue towards a new generation of lightweight high-performance metallic materials through customized phase engineering induced by interstitial atoms.