Achieving high oxygen tolerance in Ti6Al4V: Copper-oxygen co-doping strategy for ultrahigh strength-ductility balance

• Cu/O co-doping creates α s nanoprecipitates and regulates lattice in Ti6Al4V, overcoming oxygen embrittlement. • α s nanoprecipitates are formed via Cu/O synergy: O stabilizes α s phase; Cu-rich zones enable intragranular nucleation. • Achieves ultrahigh strength-ductility (σUTS=1635 MPa, El=5.3%) with high oxygen (0.62 wt.%). • High oxygen tolerance and ductility originate from synergistic lattice regulation and oxygen redistribution. Conventional α + β Ti6Al4V alloys lack sufficient strengthening mechanisms, limiting strength. While oxygen (O) offers a cost-effective strengthening route, exceeding ∼ 0.33 wt% causes significant embrittlement. Here, we explored how to efficiently utilize interstitial oxygen to enhance the mechanical properties of Ti6Al4V. The copper oxide (CuO) was innovatively employed as a precursor to completely dissolve into Ti6Al4V matrix, interstitial O and substitutional Cu atoms were simultaneously utilized to strengthen the primary α-phase (α p ) while inducing the abundant secondary-α (α s ) nanoprecipitates. Surprisingly, the introduction of Cu element facilitated control of lattice distortion and redistributed oxygen between α p and β-transformed (β trans ) structure, resulting in the Ti6Al4V-2.5CuO (wt.%) alloy with high oxygen tolerance (0.62 wt%) and an ultra-high ultimate strength of ∼ 1635 MPa and a favorable ductility of ∼ 5.3 %. The dual effect of interstitial solid solution strengthening and α s precipitation strengthening were achieved under the Cu/O interaction. Additionally, the addition of Cu promoted the oxygen redistribution and activation of the basal < a > and pyramidal < c + a > slip systems, thereby ensuring improved ductility. This study presented a novel strategy for high-strength Ti alloys using interstitial oxygen, maximizing strengthening while mitigating embrittlement.