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Polysynthetic twinned TiAl single crystals for high-temperature applications

Nature Materials volume 15, pages 876–881 (2016)Cite this article

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Abstract

TiAl alloys are lightweight, show decent corrosion resistance and have good mechanical properties at elevated temperatures, making them appealing for high-temperature applications. However, polysynthetic twinned TiAl single crystals fabricated by crystal-seeding methods face substantial challenges, and their service temperatures cannot be raised further. Here we report that Ti–45Al–8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods. Samples with 0° lamellar orientation exhibit an average room temperature tensile ductility of 6.9% and a yield strength of 708 MPa, with a failure strength of 978 MPa due to the formation of extensive nanotwins during plastic deformation. At 900 °C yield strength remains high at 637 MPa, with 8.1% ductility and superior creep resistance. Thus, this TiAl single-crystal alloy could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace.

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Figure 1: Optical micrographs of directionally solidified Ti–45Al–8Nb PST single crystals at different withdrawal rates.
Figure 2: Lamellar microstructure of a Ti–45Al–8Nb well-aligned PST single crystal before and after tensile test at ambient temperature.
Figure 3: Mechanical properties of Ti–45Al–8Nb PST single crystals as a function of temperature and the microstructure after tension.
Figure 4: Creep properties of well-aligned Ti–45Al–8Nb PST single crystals with the 0° lamellar orientation and the commercial Ti–48Al–2Cr–2Nb polycrystalline alloy at different stresses at 900 °C in air.

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Acknowledgements

The authors are grateful for financial support from the National Key Basic Research Program of China (grant 2011CB605504), and a Project Funded by PAPD of Jiangsu Higher Education Institutions. We thank F. T. Kong, X.-Q. Chen, Y. Chen, G. D. Tang, H. Nan, J. C. Li and X. Y. Cheng for beneficial discussions. C.T.L. was supported by internal funding from City University of Hong Kong, Kowloon, Hong Kong.

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Author notes

  1. Guang Chen, Yingbo Peng, Gong Zheng and Zhixiang Qi: These authors contributed equally to this work.

Authors and Affiliations

  1. Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China

    Guang Chen, Yingbo Peng, Gong Zheng, Zhixiang Qi & Minzhi Wang

  2. Aviation Key Laboratory of Science and Technology on Materials Testing and Evaluation, Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Key Laboratory of Aeronautical Materials Testing and Evaluation, Beijing Institute of Aeronautical Materials, Beijing 100095, China

    Huichen Yu & Chengli Dong

  3. Department of Mechanical and Biomedical Engineering, Centre for Advanced Structural Materials, CSE, City University of Hong Kong, Hong Kong, China

    C. T. Liu

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  1. Guang Chen
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Contributions

G.C. designed and supervised the project. Y.B.P. synthesized the PST samples. G.Z. conducted the quantitative calculation of the anisotropy of interfacial energy. Z.X.Q. and M.Z.W. performed experiments and analysed the data. H.C.Y. and C.L.D. performed high-temperature mechanical tests. C.T.L. assessed the outcomes. G.C., Y.B.P., G.Z., Z.X.Q., M.Z.W. and C.T.L. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Guang Chen or C. T. Liu.

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Chen, G., Peng, Y., Zheng, G. et al. Polysynthetic twinned TiAl single crystals for high-temperature applications. Nature Mater 15, 876–881 (2016). https://doi.org/10.1038/nmat4677

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