Precipitation processes in the beta-titanium alloy Ti-5Al-5Mo-5V-3Cr

Coakley, James and Vorontsov, Vassili A. and Jones, Nicholas G. and Radecka, Anna and Bagot, Paul A.J. and Littrell, Kenneth C. and Heenan, Richard K. and Hu, Frédéric and Magyar, Andrew P. and Bell, David C. and Dye, David (2015) Precipitation processes in the beta-titanium alloy Ti-5Al-5Mo-5V-3Cr. Journal of Alloys and Compounds, 646. pp. 946-953. 34520. ISSN 0925-8388 (

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Abstract Precipitate evolution in Ti-5Al-5Mo-5V-3Cr-0.3Fe wt.% (Ti-5553) has been studied in-situ by small angle neutron scattering (SANS) during a two step ageing heat treatment of 300°C/8h+500°C/2 h. The first heat treatment step precipitates ω, with a corresponding increase in hardness of ∼15% compared to quenched material. The second heat treatment step precipitates fine scale α from the ω phase, with a ∼90% increase in hardness compared to quenched material. The SANS measurements are complemented by atom probe tomography (APT) to give compositional information, ex-situ transmission electron microscopy (TEM) to confirm phase identification and size distribution locally, and X-ray diffraction (XRD) for additional confirmation of phase identification. The ω phase is depleted in all the solute additions following 300°C/8 h ageing heat treatment. The volume fraction of the ω phase from APT is estimated to be ∼7%. SANS modelling is consistent with disc shaped particles for the ω phase. The mean particle diameter increases from ∼7.5 nm to 9.5 nm diameter between 1 h and 8 h heat treatment at 300 °C, while the thickness increases from ∼4 nm to ∼5 nm. The SANS model estimates the volume fraction to be ∼10% for the 8 h heat treatment, using the phase compositions from APT.