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

ABSTRACT 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.