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 similar to 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 alpha + beta dual-phase with basal alpha 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.

Automated summary

Oxygen is known to reduce the ductility of Ti alloys, but a new equiaxed Ti-8Nb-2Fe-0.66O alloy has been developed with ultrahigh yield strength and good tensile ductility. The oxygen-containing alloy is 87% stronger than the oxygen-free base alloy, with minimal loss in ductility. Oxygen interstitials play a dual role, strengthening the alloy by pinning dislocations and suppressing martensitic transformation, while also promoting multiple dislocation activities for good ductility. This work demonstrates a new approach to developing high-strength Ti alloys by doping oxygen interstitials, utilizing its beneficial strengthening factor while avoiding embrittlement.