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Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy
Shanghai Jiao Tong Univ, Shanghai Key Lab Adv High Temp Mat & Precis Formi, Sch Mat Sci & Engn, Shanghai 200240, Peoples R China..
Shanghai Jiao Tong Univ, Shanghai Key Lab Adv High Temp Mat & Precis Formi, Sch Mat Sci & Engn, Shanghai 200240, Peoples R China..
Shanghai Jiao Tong Univ, Shanghai Key Lab Adv High Temp Mat & Precis Formi, Sch Mat Sci & Engn, Shanghai 200240, Peoples R China..
Shanghai Jiao Tong Univ, Shanghai Key Lab Adv High Temp Mat & Precis Formi, Sch Mat Sci & Engn, Shanghai 200240, Peoples R China..
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2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 165, p. 215-227Article in journal (Refereed) Published
Abstract [en]

The formation and temporal evolution of the modulated structure in a lamellar gamma-based Ti-45Al-8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 degrees C in the alpha(2) lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed alpha(2), named as alpha(2-II) hereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and alpha(2) is about 2 at 600 degrees C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 +/- 0.2) x 10(-22) m(2)s(-1) in the alpha(2) lamellae. Significant precipitation hardening effect of the O phase has been revealed for the alpha(2) lamellae and gamma/(alpha(2)+O) lamellar microstructure, which is supposed to be attributed to refining the alpha(2) lamellae associated with elastic strain energy from the alpha(2) -> O phase transformation and introducing the interface between the modulated lamella and adjacent gamma phase. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2019. Vol. 165, p. 215-227
Keywords [en]
Titanium aluminides, Orthorhombic phase, Microstructural evolution, Diffusion, Nano-indentation
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-244506DOI: 10.1016/j.actamat.2018.11.041ISI: 000457665100020Scopus ID: 2-s2.0-85057440485OAI: oai:DiVA.org:kth-244506DiVA, id: diva2:1301349
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QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-04Bibliographically approved

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Lu, SongVitos, Levente

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