A review of the metastable omega phase in beta titanium alloys: the phase transformation mechanisms and its effect on mechanical properties

ABSTRACT

Since its discovery in 1954, the omega (ω) phase in titanium and its alloys has attracted substantial attention from researchers. The β-to-ω and ω-to-α phase transformations are central to β-titanium alloy design, but the transformation mechanisms have been a subject of debate. With new generations of aberration-corrected transmission electron microscopy and atom probe tomography, both the spatial resolution and compositional sensitivity of phase transformation analysis have been rapidly improving. This review provides a detailed assessment of the new understanding gained and related debates in this field enabled by advanced characterization methods. Specifically, new insights into the possibility of a coupled diffusional-displacive component in the β-to-ω transformation and key nucleation driving forces for the ω-assisted α phase formation are discussed. Additionally, the influence of ω phase on the mechanical properties of β-titanium alloys is also reviewed. Finally, a perspective on open questions and future direction for research is discussed.

KEYWORDS:

• Titanium alloys
• omega phase
• beta phase
• microstructure
• mechanical behavior
• phase transformations
• atom probe tomography
• transmission electron microscopy

Acknowledgements

This work was made possible through the support of the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DE-SC0014664. A portion of the funding for this research was supported by the National Science Foundation Division of Material Research, under Grant No. DMR-1607942 through the Metals and Metallic Nanostructures (MMN) program (JB & CJB). A portion of the funding for this research was supported by the US Department of Energy, Office of Basic Energy Science through grant No. DE-SC0001525 (JB & CJB). AD would like to acknowledge the funding from the Laboratory Directed Research and Development program as a part of the Solid Phase Processing Initiative at Pacific Northwest National Laboratory (PNNL).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Science Foundation [grant number DMR-1607942]; Office of Science [grant number DE-SC0001525]; Pacific Northwest National Laboratory Laboratory Directed Research and Development Program.