Atomistic simulations of high-temperature creep in nanotwinned TiAl alloys

Abstract

TiAl alloys exhibit high specific strength and stiffness and especially excellent mechanical properties at elevated temperatures, making them appealing for high-temperature applications. Understanding the underlying creep mechanisms of TiAl alloys is essential for their design, fabrication and high-temperature applications. Here, we performed a series of large-scale atomistic simulations for high-temperature creep in nanocrystalline and nanotwinned γ-TiAl alloys. Our simulation results showed the influences of applied stress, grain size and temperature on the creep behaviors and mechanisms of nanocrystalline and nanotwinned TiAl alloys, which are in good agreement with predictions based on the classic Bird–Dorn–Mukherjee equation. More interestingly, our simulation results showed that for the nanotwinned sample with a mean grain size of 20 nm under high applied stress, there exists a critical twin thickness of 2.79 nm, corresponding to the lowest creep rate, which is ascribed to the creep mechanism changing from dislocation nucleation and slip to detwinning due to twin boundary migration. Our current study sheds light on high-temperature creep mechanisms for nanocrystalline and nanotwinned TiAl alloys, which guides the design and fabrication of TiAl alloys with enhanced creep resistance.