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

James Coakley, Vassili A. Vorontsov, Nicholas G. Jones, Anna Radecka, Paul A.J. Bagot, Kenneth C. Littrell, Richard K. Heenan, Frédéric Hu, Andrew P. Magyar, David C. Bell, David Dye

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Abstract

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.

Original languageEnglish
Article number34520
Pages (from-to)946-953
Number of pages8
JournalJournal of Alloys and Compounds
Volume646
DOIs
Publication statusPublished - 7 Jul 2015

Keywords

  • atom probe tomography (APT)
  • precipitation
  • small angle neutron scattering (SANS)
  • titanium alloys
  • transmission electron microscopy (TEM)

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