Addressing Oxygen Embrittlement in Additively Manufactured Titanium via Cu‐Mediated Interstitial Site Engineering

The strength-ductility trade-off in oxygen-containing titanium alloys has long been limited by the embrittling nature of octahedral interstitial oxygen (oct-O). Herein, by integrating controlled laser powder bed fusion (L-PBF) processing with Cu─O co-alloying, we achieve, for the first time, the thermodynamic stabilization of hexahedral oxygen (hex-O) configurations, which redefines the role of oxygen in titanium alloys. We showcase such interstitial engineering of oxygen relies on two key regimes: (1) Cu-induced charge redistribution creates an electronic environment that preferentially stabilizes hex-O sites through strong d-p orbital hybridization, (2) rapid solidification process enabled by L-PBF effectively suppresses the Ti─Cu excessive eutectoid reaction, preserving the integrity of strong Cu─O dipole chemical bonds. Mechanistically, hex-O enhances <c>-component dislocation activity through localized lattice distortion while maintains effective strain hardening via long-range interactions with dislocations. This atomic-scale manipulation in interstitial O enables an unprecedented strength-ductility synergy of the titanium alloy, with a yield strength of 1121 MPa and a fracture elongation of 10.2%. Our work demonstrates a new pathway for tailoring the mechanical properties of oxygen-tolerant titanium alloys via interstitial engineering.