The microstructure evolution and phase transformation behavior of a β-solidifying γ-TiAl alloy during creep

• Published in: Progress in natural science 2023-04, Vol.33 (2), p.193-202
• Main Authors: Liu, Yan, Li, Jinshan, Tang, Bin, Wang, William Yi, Chu, Yudong, Zhu, Lei, Bi, Weiqing, Chen, Xiaofei, Kou, Hongchao
• Format: Article
• Language: English
• Subjects: Creep behavior; Microstructure evolution; Phase transformation; TEM; TiAl alloys
• ISSN: 1002-0071
• DOI: 10.1016/j.pnsc.2023.05.002

The microstructural evolution and creep behavior of the Ti-43.5Al–4Nb–1Mo-0.1B alloy have been investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The excellent creep property was obtained with a fully lamellar (FL) microstructure containing the least grain boundary βo phase (GB-βo). TEM results revealed that after creep testing the α2 →βo phase transformation was observed in the FL microstructure. The formation βo phase is associated with the accumulation of Mo element, which is confirmed by the energy-dispersive X-ray spectroscopy (EDS). Moreover, the formation of βo precipitation in α2 lamellae effectively decreased the generation of dislocations in (α2/γ) lamellae, thereby improving the creep resistance. For the near gamma (NG) microstructure of the as-forged sample, a large number of dislocations and dislocation tangles were observed in the globular γ phase (γ-glob), which are considered to be the dominant creep mechanism. Moreover, the ellipsoidal ωo phase was observed in the GB-βo phase, accompanying with dislocations and sub-boundaries formation. In sum, the excellent creep property of the β-solidifying γ-TiAl alloy is attributed to the fine FL structure with a small amount of GB-βo phase and the formation of βo precipitation in (α2/γ) lamellae. [Display omitted] •The most excellent creep property is obtained by a fully lamellar structure of the TNM alloy.•The creep mechanism of the as-forged sample is dominated by dislocation movement.•After creep, the ωo precipitation grew up in βo matrix.•The phase transformations of α2.→ βo were observed in (α2/γ) lamellae.