Acta Metallurgica Sinica (English Letters) ›› 2020, Vol. 33 ›› Issue (12): 1591-1600.DOI: 10.1007/s40195-020-01108-x

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Creep-Induced Phase Instability and Microstructure Evolution of a Nearly Lamellar Ti-45Al-8.5Nb-(W, B, Y) Alloy

Xuyang Wang1, Jieren Yang1,2(), Rui Hu1,2, Zitong Gao1, Jinguang Li1, Hengzhi Fu1   

  1. 1State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072, China
    2Shaanxi Key Laboratory of High-Performance Precision Forming Technology and Equipment, Northwestern Polytechnical University, Xi’an, 710072, China
  • Received:2020-03-16 Revised:2020-04-24 Accepted:2020-05-15 Online:2020-12-10 Published:2020-12-11
  • Contact: Jieren Yang


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 γα2 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.

Key words: TiAl based alloy, Creep, Microstructural stability, Transmission electron microscopy (TEM)