Discontinuous yielding behavior of β phase containing TiAl alloy during high-temperature deformation process

γ-TiAl base alloys are promising high-temperature materials for aviation and aerospace applications due to their low density, exceptional high-temperature strength and good oxidation resistance. However, low ductility and poor hot workability limit the use of such alloys. The introduction of β phase appears to be effective to improve the hot workability of TiAl alloys, while the influence of β phase on hot deformation behavior of TiAl alloy has been rarely investigated until now. In this work, high-temperature compression experiments of β phase containing TiAl alloy (Ti-42Al-9V-0.3Y) were conducted on a Gleeble-1500 thermal simulation machine at 1000-1200°C and strain rates of 0.001-1.0 s^-1. The hot deformation behavior of the TiAl alloy was investigated and the discontinuous yielding mechanism was analyzed. The results show that the main deformation softening mechanism was the dynamic recovery (DRV) of β phase and dynamic recrystallization (DRX) of γ phase. The discontinuous yielding behavior was closely related to the DRV in β phase and the multiplication of the superdislocation with Burgers vector b=1/2(112) in γ phase. The established dislocation dynamics model based on the Orowan equation in the present work could reasonably explain the causes for the discontinuous yielding phenomenon, indicating that the rapid increase of mobile dislocation density and small dislocation motion velocity sensitivity m^* could induce the discontinuous yielding of the TiAl alloy. In addition, the fluctuating yielding behavior was attributed to the interaction effect of dislocation slip and twin at lower temperatures of 1100-1150°C and higher strain rate of 1 s^-1.