New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys

Tong Li; Damon Kent; Gang Sha; Leigh T Stephenson; Anna V Ceguerra; Simon P Ringer; Matthew S Dargusch; Julie M Cairney

doi:10.1016/j.actamat.2015.12.046

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New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys

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New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys

Tong Li, Damon Kent, Gang Sha, Leigh T Stephenson, Anna V Ceguerra, Simon P Ringer, Matthew S Dargusch and Julie M Cairney

Acta Materialia, Vol.106, pp.353-366

2016

DOI: https://doi.org/10.1016/j.actamat.2015.12.046

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Abstract

titanium alloys

phase transformations

atom probe tomography

high resolution electron microscope (HREM)

For multicomponent near-β alloys, we have investigated the mechanisms responsible for the β-to-ω and ω-to-α phase transformations upon isothermal ageing at 573 K. Experimental evidence from atom probe tomography and aberration-corrected high-resolution transmission electron microscopy indicates that the formation of isothermal ω involves a structural reconstruction assisted by nanoscale spinodal decomposition of the β matrix, prior to the specific chemistry change required to form ω, rather than a mixed-mode process with structure and chemistry changes occurring simultaneously as has been previously suggested. First, incommensurate embryonic ω evolve via a displacive mechanism within Mo-lean regions created by second-order coherent spinodal decomposition of the β matrix. The subtle spinodal decomposition in β and chemistry of embryonic ω are carefully analysed by an advanced atom probe data analysis algorithm. When the size of embryonic É· exceeds a critical value, commensurate isothermal É· forms through the exit of the other alloying solutes. O-rich regions present at the isothermal ω/β interface provide potent sites for the formation of α. The concurrent compositional partitioning of solutes in É· and α indicates the transformation from ω to α involves both a rapid lattice reconstruction at the ω/α interface and a slow Al diffusion at the α/β, therefore a mixed-mode displacive-diffusive process. This study provides novel experimental evidence to understand the much-disputed transformation processes and elucidate the mechanisms responsible for these important phase transformations.

Details

Title: New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys
Authors: Tong Li (Author)
Damon Kent (Author) - University of the Sunshine Coast - Faculty of Science, Health, Education and Engineering
Gang Sha (Author) - Nanjing University of Science and Technology, China
Leigh T Stephenson (Author) - University of Sydney
Anna V Ceguerra (Author) - University of Sydney
Simon P Ringer (Author) - University of Sydney
Matthew S Dargusch (Author) - The University of Queensland
Julie M Cairney (Author) - University of Sydney
Publication details: Acta Materialia, Vol.106, pp.353-366
Publisher: Pergamon
Date published: 2016
DOI: 10.1016/j.actamat.2015.12.046
ISSN: 1359-6454
Organisation Unit: School of Science and Engineering - Legacy; University of the Sunshine Coast, Queensland; School of Science, Technology and Engineering
Language: English
Record Identifier: 99449580602621
Output Type: Journal article

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Collaboration types: Domestic collaboration; International collaboration
Web Of Science research areas: Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering