Oxygen-gradient titanium with high strength, strain hardening and toughness

Titanium (Ti) is sensitive to small amount of oxygen interstitials, which has a major impact on its mechanical properties. Noticeable strengthening together with rapid decline in ductility induced by oxygen solutes poses a serious limitation for processing and application of Ti alloys. Here, we alleviate this dilemma by designing a unique oxygen-gradient in pure Ti, achieving a nontrivial combination of ultra-hardenability, high strength, toughness, and enhanced strain hardening rate. Plausible mechanism for such an oxygen-regulated plasticity in hexagonal Ti is proposed, which depends on twinning coordinating plasticity after yielding and oxygen-solute mediated dislocation slip subsequently. The dislocations glide on the common prismatic plane at low oxygen concentration, then prevail on the unusual 1st order pyramidal plane and then transfer to the peculiar basal plane and the 2nd order pyramidal plane with increasing oxygen content. These findings provide an effective mean to optimize pure Ti with desirable mechanical performance.