Creep behavior and related phase precipitation of a creep-resistant Y₂O₃-bearing high Nb containing TiAl alloy

In this study, a creep-resistant Ti-45Al-6Nb-2.5V-0.15Y₂O₃ alloy was developed, and the microstructure characteristics at different creep stages at 850 °C under 200 MPa was investigated in detail. The results show that creep deformation of this alloy depends not only on dislocation slip and climb of γ phase, but also on α₂ phase due to the activation of 2c→+a→ slip system. Meanwhile, 1/6<112¯111 twinning systems are initiated, gradually leading to twin intersections. Then, the interactions among dislocation, twin boundary and Y₂O₃ particle cause creep hardening. Whereas the occurrence of dynamic recrystallization softens the alloy. When entering the accelerated creep stage, the surface damage caused by oxidation and the bulk damage caused by void nucleation will result in the increase of creep rate until fracture. In addition, metastable TiAl₂ phase with ZrGa₂ structure nucleates on the dislocation lines inside γ phase during creep, obeying an orientation relationship of [001]_TiAl//[001]_TiAl2, (020)_TiAl//(200)_TiAl2. Meanwhile, TiAl₂ phase maintains a small planar disregistry of 1.54% with γ matrix. With the increase of creep deformation or creep time, more TiAl₂ phases gradually nucleate and grow.