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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. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. 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:uu:diva-378527DOI: 10.1016/j.actamat.2018.11.041ISI: 000457665100020OAI: oai:DiVA.org:uu-378527DiVA, id: diva2:1298682
Available from: 2019-03-25 Created: 2019-03-25 Last updated: 2019-03-25Bibliographically approved

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Vitos, Levente

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