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<p>The α<sub>2</sub> decomposition in γ-TiAl-based alloys during long-term service at elevated temperatures affects the mechanical properties and reliability of components. However, the formation mechanism of the precipitates, β<sub>0</sub> phase in Mo-modified γ-TiAl alloys in particular, has not been clarified. In the present work, the formation of a novel α<sub>2</sub> + β<sub>0</sub> modulated microstructure in Ti–43.5Al–4Nb–1Mo–0.5B (at%) alloy at 700&#xa0;°C has been investigated by using scanning and transmission electron microscopy. Six equivalent β<sub>0</sub> phase variants nucleate at the α<sub>2</sub>/γ lamellar interfaces and grow into a plate shape within α<sub>2</sub> lamellae. The β<sub>0</sub> phase mainly exists as clusters of three or multiple plates. This distinctive growth pattern exhibits notable differences from conventional phase transformation modes, offering a fresh perspective for comprehending phase transformation behaviors. The formation of the β<sub>0</sub> phase in α<sub>2</sub> lamellae is controlled by the diffusion of Nb/Mo atoms (mainly Mo). The lattice distortion between the β<sub>0</sub> and α<sub>2</sub> phases promotes the nucleation of new β<sub>0</sub> plates, revealing the significant impact of interphase interactions on the microstructural evolution. The lattice of the central α<sub>2</sub> phase enclosed by β<sub>0</sub> variants is rotated around the [0001]<sub>α2</sub> axis of the α<sub>2</sub> matrix by 10.53° to minimize the elastic strain energy. The results offer insights into the mechanism of α<sub>2</sub> decomposition as a function of alloy composition, providing a basis for controlling the microstructure and improving the mechanical properties of β-stabilized γ-TiAl alloys, and thus opening new window of opportunity in the design and development of high-temperature structural materials.</p> Graphical abstract <p></p>

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Formation of a novel α2 + β0 modulated microstructure in a Mo-modified γ-TiAl alloy

  • 期刊论文

  • 发表日期：

    2025年8月25日

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  • Zhi-Chun Zhou,
  • Ren-Ci Liu,
  • Xin-Ao Chen,
  • Qing-Miao Hu,
  • Ru-Xin Cao,
  • Ying-Ying Shen,
  • Yu-You Cui,
  • Rui Yang

摘要

The α2 decomposition in γ-TiAl-based alloys during long-term service at elevated temperatures affects the mechanical properties and reliability of components. However, the formation mechanism of the precipitates, β0 phase in Mo-modified γ-TiAl alloys in particular, has not been clarified. In the present work, the formation of a novel α2 + β0 modulated microstructure in Ti–43.5Al–4Nb–1Mo–0.5B (at%) alloy at 700 °C has been investigated by using scanning and transmission electron microscopy. Six equivalent β0 phase variants nucleate at the α2/γ lamellar interfaces and grow into a plate shape within α2 lamellae. The β0 phase mainly exists as clusters of three or multiple plates. This distinctive growth pattern exhibits notable differences from conventional phase transformation modes, offering a fresh perspective for comprehending phase transformation behaviors. The formation of the β0 phase in α2 lamellae is controlled by the diffusion of Nb/Mo atoms (mainly Mo). The lattice distortion between the β0 and α2 phases promotes the nucleation of new β0 plates, revealing the significant impact of interphase interactions on the microstructural evolution. The lattice of the central α2 phase enclosed by β0 variants is rotated around the [0001]α2 axis of the α2 matrix by 10.53° to minimize the elastic strain energy. The results offer insights into the mechanism of α2 decomposition as a function of alloy composition, providing a basis for controlling the microstructure and improving the mechanical properties of β-stabilized γ-TiAl alloys, and thus opening new window of opportunity in the design and development of high-temperature structural materials.

Graphical abstract