Substantially strengthening a dual-phase titanium alloy by moderate oxygen doping

As one of the detrimental ingredients, oxygen can, even in a small amount, substantially reduce the ductility of Ti alloys. Here, rather than being discouraged by the negative effects of oxygen on ductility, an equiaxed dual-phase Ti-8Nb-2Fe-0.66O (wt.%) alloy showing ultrahigh yield strength (1386 MPa) and good tensile ductility (fracture elongation ∼10.8%) was developed. The oxygen-containing alloy is 87% stronger than the oxygen-free base alloy whereas the ductility loss is marginal. The effects of oxygen interstitials can be twofold: they led to significant solid-solution strengthening by pinning dislocations and suppressing stress-induced martensitic transformation; the equiaxed α + β dual-phase with basal α texture doped by oxygen promoted multiple 〈c + a〉-type and 〈a〉-type dislocation activities that guaranteed good ductility. This work demonstrates a new avenue to develop high-strength Ti alloys by doping oxygen interstitials, which takes full advantage of the beneficial strengthening factor of oxygen while avoiding its detrimental embrittlement effect.