On revealing the mechanisms involved in brittle-to-ductile transition of fracture behaviors for γ-TiAl alloy under dynamic conditions

To understand the high-temperature behaviors of γ-TiAl is essential for its applications in aerospace industries. In this study, the high-temperature mechanical tests were carried out with strain rates ranging from 0.001 to 0.1 s⁻¹ for the forged Ti-46Al-5Nb-1.8Cr-0.2Ta-0.1B alloy. The dynamic behaviors, fracture modes and microstructure evolution at elevated temperatures were analyzed to reveal the mechanisms involved in damage evolution. The results show that the brittleness of γ-TiAl is enhanced by strain rate hardening, and the brittle-to-ductile transition temperature (BDTT) increases with the increase of strain rates. The fracture morphology shows that the fracture characteristics transfer from the brittle fracture with mixed mode of intergranular and transgranular below and within the BDTT to the ductile fracture above BDTT. In addition, micro-cracks appear in fracture zones at the transitory stage, and cavities appear at the ductile stage, which is related to dynamic recrystallization (DRX). In this case, it is deduced that the brittle-to-ductile transition is induced by the competition between plastic deformation and crack propagation, and the results can be used to optimize the processing parameters towards high surface integrity when manufacturing γ-TiAl components.