High Compressive Strength of Bulk Polycrystalline ω Phase in Pure Titanium

Titanium has the highest strength-to-weight ratio of any metal. Titanium and its alloys are strong and lightweight, and are therefore used in many industrial applications. The ω-phase is known to form metastably during quenching and aging processes of titanium alloys, and the presence of this phase causes increases in strength and decreases in ductility. However, the mechanical properties of the ω-phase are poorly measured because this phase precipitates as nanograins in titanium alloys. Here we report the fabrication of bulk polycrystalline ω-phase samples in pure titanium under high pressure and temperature conditions of 12 GPa and 400°C. They are single-phase and randomly oriented polycrystalline materials with an average grain size of 21 ± 8 µm. The 0.2% offset yield strength was determined from compressive stress-strain curves to be 913 ± 3 MPa. The ω-phase is more than twice as strong as the α-phase in pure titanium and could be used as a non-toxic structural material for biomedical applications.