4.7 Article

Characterization of primary, secondary and tertiary {2021}<1014> successive internal twins in the D019 ordered hexagonal α2-Ti3Al phase

期刊

ACTA MATERIALIA
卷 222, 期 -, 页码 -

出版社

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2021.117391

关键词

Titanium aluminides; Deformation twins; Transmission electron microscopy; Interface structure

资金

  1. National Natural Science Foundation of China [51971175]
  2. Natural Science Basic Research Plan of Shaanxi Province [2020JM-097]
  3. State Key Laboratory of Solidification Processing [2021-TS-05]
  4. State Key Laboratory of Advanced Metals and Materials [2020-ZD03]
  5. 111 Project [B20028]

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This study revealed a novel internal twinning mechanism of the alpha(2) phase in a TiAl alloy deformed at high temperature, showing three generations of twins. The findings shed light on the ductility of the alloy and provide important information on the complex twinning mechanisms in hexagonal structures.
Due to the lack of independent slip systems and the difficulty in mechanical twinning, D0(19) ordered alpha(2)-Ti3Al phase is known to be of substantial mechanical anisotropy, which partly accounts for the low ductility of two-phase (alpha(2)+gamma) TiAl alloys. However, recent studies have shown that in Al-rich alpha(2) phase compression deformation twins can be activated, which could be beneficial for the ductility of the alloys. In the present study, for the first time, we have revealed a novel internal twinning mechanism of alpha(2) phase in a TiAl alloy deformed at high temperature. Three twin generations of a common type {2021}< 1014 > were revealed: Secondary twins formed within the primary twin, and tertiary twins formed in the secondary twin. It is important to note that this internal twin structure can only be observed in the < 2116 > direction but not the commonly used < 1120 > direction. The shear plane P of all twin variants is of type {1210}. Due to the variation of the twinning elements between the twin variants, the twinning shear is blunted. The interfaces between the twin variants are characterized by high-resolution electron microscopy. Special attention was paid to the structure of the coherent and incoherent twin boundaries. The effect of chemical ordering is discussed. Our results also shed light on the complex twinning mechanisms in hexagonal structures. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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