Oxygen and strain co-driven cubic phase in Ti and its mechanical response

Oxygen is an important strengthening element for titanium (Ti) alloys. The face-centered cubic ( fcc ) structure in Ti alloys attracts attention due to its formation mechanism and superior mechanical properties. This study utilized high-pressure torsion to create a nanocrystalline hexagonal close-packed ( hcp ) Ti matrix with fcc phase lamellae in various Ti-O alloys. We show that both oxygen content and strain can be tuned to control the formation of the fcc phase. At low oxygen concentrations, the fcc phase appears as an intergranular structure, while at higher oxygen levels, it evolves into a lath-like morphology. In addition to the hcp / fcc normal orientation relationships, a new ω / fcc interface orientation of {0002} ω ||{220} fcc is identified. Oxygen atoms are found to preferentially distribute in fcc lamellae, which is supported by density functional theory. Energy loss near-edge structure analysis indicates that oxygen atoms become more interstitial in fcc lamellae than in the matrix. This oxygen-mediated fcc structure enhances strength while maintaining ductility, providing a novel mechanism for stabilizing the fcc phase at grain boundaries. It demonstrates a new strategy for producing Ti alloys with high strength and reasonable ductility by controlling the O level and strain.