High strength and high work hardening rate in oxygen gradient Ti-15Mo alloy.

• Oxygen gradient Ti-15Mo alloy is fabricated via compositional gradient design. • It exhibits optimal strength-ductility balance along with high work hardening rate. • Coupling deformation of twinning and slip is achieved due to oxygen gradient. • The crack tips is blunted by twins and GNDs, avoiding the premature necking. The low work hardening is a prominent deficiency for high-strength titanium (Ti) alloys. The gradient design of oxygen content was adopted to realize the coupling deformation of {332}<113> twinning and dislocation slip in the Ti-15Mo alloy. This oxygen gradient alloy exhibited an optimal balance of yield/tensile strength (700 and 848 MPa) and elongation (25 %), with remarkable work hardening behavior. The dominated dislocation slip deformation and the solution strengthening of oxygen atoms in the oxygen-rich region resulted in a remarkable increase in yield strength. The successive formation of {332}<113> twins and piled-up geometrically necessary dislocations around the twin boundaries in the oxygen-free region induced remarkable back stress strengthening, maintaining the high work hardening rate, which resulted in a stable increase in strength. The twins and dislocations formed at the crack tips effectively hindered the cracking behavior, avoiding premature necking. The present study provides a novel idea for designing oxygen layer-distributed Ti alloys, which further improves the strength–ductility tradeoff. [Display omitted] [ABSTRACT FROM AUTHOR]