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

Li, Tong, Kent, Damon, Sha, Gang, Stephenson, Leigh T., Ceguerra, Anna V., Ringer, Simon P., Dargusch, Matthew S. and Cairney, Julie M. (2016) New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys. Acta Materialia, 106 353-366. doi:10.1016/j.actamat.2015.12.046

Author Li, Tong
Kent, Damon
Sha, Gang
Stephenson, Leigh T.
Ceguerra, Anna V.
Ringer, Simon P.
Dargusch, Matthew S.
Cairney, Julie M.
Title New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys
Journal name Acta Materialia   Check publisher's open access policy
ISSN 1359-6454
Publication date 2016-03-01
Year available 2016
Sub-type Article (original research)
DOI 10.1016/j.actamat.2015.12.046
Open Access Status DOI
Volume 106
Start page 353
End page 366
Total pages 14
Place of publication Doetinchem, The Netherland
Publisher Elsevier
Collection year 2017
Language eng
Formatted abstract
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 ɷ exceeds a critical value, commensurate isothermal ɷ 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 ɷ 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.
Keyword Atom probe tomography
High resolution electron microscope (HREM)
Phase transformations
Titanium alloys
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mechanical & Mining Engineering Publications
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