Abstract
Microstructure degradation and stress-induced transformation of a high Nb-containing TiAl alloy with nearly lamellar microstructure during creep were investigated. Tensile creep experiments were performed at 800, 850 and 900 °C under 150 MPa in air. Microstructures before and after creep tests were examined using scanning and transmission electron microscopy (SEM and TEM). Dislocations within the lamellar structure and βo(ω) region and twin intersection in massive γ grains were investigated. Dislocation sliding played a critical role in the deformation of ωo phase, which preferentially occurred on the (0002)ωo plane. Possible deformation mechanisms were revealed. A stress-induced γ → α2 phase transformation took place during the creep test at 850 and 900 °C. α2 lamella could directly decompose into the ωo phase at 850 °C. The instability of high-temperature microstructure can weaken the creep resistance and promote the plastic deformation of the lamellar matrix, thus could be detrimental to the creep properties. The correlations between creep properties and microstructure instability were discussed.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos. 51774238 and 51971176), the 2018 Joint Foundation of Ministry of Education for Equipment Pre-research (No. 6141A020332), the State Key Laboratory for Advanced Metal and Materials Foundation (No. 2014-ZD06) and the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University (No. LZUMMM2020008). Analytical & Testing Center in Northwestern Polytechnic University are also acknowledged sincerely for the support.
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Wang, X., Yang, J., Hu, R. et al. Creep-Induced Phase Instability and Microstructure Evolution of a Nearly Lamellar Ti–45Al–8.5Nb–(W, B, Y) Alloy. Acta Metall. Sin. (Engl. Lett.) 33, 1591–1600 (2020). https://doi.org/10.1007/s40195-020-01108-x
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DOI: https://doi.org/10.1007/s40195-020-01108-x