Harnessing strengthening-metastability synergy for extreme work hardening in additively manufactured titanium alloys

Rapid bottom-up fabrication via additive manufacturing (AM) unlocks unprecedented design freedom for geometrically complex and lightweight titanium (Ti) alloys, a critical material for next-generation aerospace systems and 3C (computer, communication and consumer electronics) products. However, conventional AM Ti alloys face a persistent dilemma: achieving yield strengths above 1 GPa catastrophically degrades work hardening (typically < 2 GPa) and uniform ductility (< 5%). Here, we harness a strengthening-metastability synergy strategy via AM to demonstrate the powerful CoCrNi additive-strengthened Ti alloy with an outstanding combination of loss-free yield strength and drastically enhanced work hardening. Unlike traditional metastable alloys with incomplete phase transformation (β → β/α'), our design triggers a complete two-step martensitic transformation (β → β/α' → α'/α' twin) during deformation, without residual matrix and forming hierarchically mutual twin structures. This unique transformation pathway sustains a successive work hardening, achieving a record work hardening rate of 5.7 GPa and uniform elongation of 9.3% (triple that of base alloy), while maintaining 1030 MPa yield strength. The dual emphasis on synergy strategy and mechanistic innovation via the non-equilibrium AM process directly addresses the structural sector's urgent need for high-performance yet sustainable metallic solutions.