The microstructure evolution and phase transformation behavior of a beta-solidifying ?-TiAl alloy during creep

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 beta(o) phase (GB-beta(o)). TEM results revealed that after creep testing the alpha(2) -> beta(o) phase transformation was observed in the FL microstructure. The formation beta(o) phase is associated with the accumulation of Mo element, which is confirmed by the energy-dispersive X-ray spectroscopy (EDS). Moreover, the formation of beta(o) precipitation in a2 lamellae effectively decreased the generation of dislocations in (alpha(2)/gamma) 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 gamma phase (gamma-glob), which are considered to be the dominant creep mechanism. Moreover, the ellipsoidal omega(o) phase was observed in the GB-beta(o) phase, accompanying with dislocations and sub-boundaries formation. In sum, the excellent creep property of the beta-solidifying gamma-TiAl alloy is attributed to the fine FL structure with a small amount of GB-beta(o) phase and the formation of beta(o) precipitation in (alpha(2)/gamma) lamellae.

Automated summary

The microstructural evolution and creep behavior of the Ti-43.5Al-4Nb-1Mo-0.1B alloy were studied using SEM and TEM. The alloy with a fully lamellar (FL) microstructure containing the least grain boundary beta(o) phase (GB-beta(o)) exhibited excellent creep resistance. The formation of beta(o) precipitation in (alpha(2)/gamma) lamellae effectively reduced the generation of dislocations and improved creep resistance.