The effect of zirconium on the omega phase in Ti-24Nb-[0–8]Zr (at.%) alloys
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Pang, E., Pickering, E., Baik, S., Seidman, D., & Jones, N. (2018). The effect of zirconium on the omega phase in Ti-24Nb-[0–8]Zr (at.%) alloys. Acta Materialia, 153 62-70. https://doi.org/10.1016/j.actamat.2018.04.016
Ti-Nb based β-Ti alloys are a promising new class of superelastic, shape-memory, and low-modulus materials for a wide range of applications. A critical phase in β-Ti alloys is the ω phase, which greatly affects the mechanical properties and superelastic/shape-memory behaviour of these materials. Zirconium, an important alloying constituent in many β-Ti alloys, is generally regarded as an ω suppressant, but the body of evidence supporting this view is unconvincing and includes a number of conflicting reports. In this article, the role of Zr on ω phase formation in Ti-Nb alloys is clarified using X-ray diffraction, transmission electron microscopy, and atom-probe tomography. Zirconium additions were found to suppress the formation of athermal ω phase upon quenching from high temperature. However, up to 8 at.% Zr additions to a Ti-24 at.% Nb alloy had little effect on the formation of isothermal ω phase following aging at 300 °C after 100 hours. Furthermore, the isothermal ω precipitates were found to be strongly depleted in Nb but only weakly depleted in Zr. These results challenge the belief that Zr suppresses isothermal ω formation in β-Ti alloys, a result that is likely to be applicable beyond the Ti-Nb system considered here and information that can be used to assist in the design of future β-Ti alloys.
External DOI: https://doi.org/10.1016/j.actamat.2018.04.016
This record's URL: https://www.repository.cam.ac.uk/handle/1810/275143