Unraveling hot deformation behavior and microstructure evolution of nanolamellar TiAl/Ti3Al composites

Chen, Yang; Li, Jia; Liu, Bin; Wang, Jian; Liu, Nan; Ren, Siwei; Liaw, Peter K.; Fang, Qihong

doi:10.1016/j.intermet.2022.107685

Cited by 7 publications

(2 citation statements)

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“…The two kinds of interface boundaries-α 2 =γ and γ=γ-restrict and confine dislocation motion, but allow for cross slip and can act as dislocation sources. [7][8][9][10][11] The lamellar TiAl microstructure is abundant with γ=γ twin boundary interfaces and alloy design strategies rely on ultimately adjusting the number of such interfaces and simultaneously changing the lamellar thickness. [1,6,12,13] However, due to the ordering and the resulting tetragonal nature of the γ phase, three different kinds of γ=γ {111} boundaries exist-the pseudotwin (PT) boundary, with a misorientation of 60°, the 120°rotational fault boundary or rotational boundary (RB), and the true twin (TT) boundary with a rotation of 180°.…”

Section: Introductionmentioning

confidence: 99%

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How Coherent and Semi‐Coherent Interfaces Govern Dislocation Nucleation in Lamellar TiAl Alloys

Chauniyal

Janisch

2023

Adv Eng Mater

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γ/γ interfaces drive plastic deformation in lamellar TiAl alloys. Due to the ordering and resulting tetragonal nature of γ phase, γ/γ twin interfaces exist as different variants, some of which exhibit coherency stresses or semicoherent interface structures. While geometric parameters, such as the lamella spacing and orientation, are explored extensively in experiments, the isolation of individual influence of different interfaces in a nanolamellar microstructure remains a challenge. Herein, the range of γ/γ interface states is modeled using bilayers of the coherent γ/γTrueTwin, and the coherent or semicoherent γ/γPseudoTwin, and their deformation behavior is compared. It is shown that residual coherency stresses arise due to misfit accommodation in coherent γ/γPT specimens, which causes early preferential nucleation in one γ layer. Similarly, semicoherent specimens show preferential nucleation from misfit dislocations at the interface, which obeys Schmid's rule. In contrast, coherent γ/γTT specimens show no preferential nucleation and therefore exhibit higher strength. Thus, it is demonstrated that the presence of rotational γ/γ interfaces with misfit is responsible for localized and early plasticity, that lowers the strength of a lamellar microstructure. The interface type, which considers the coherency state, is used as a criterion for alloy microstructure design in the future.

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