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 $\gamma$-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.

TiAl合金在高温下表现出高的比强度和刚度，尤其是出色的机械性能，使其在高温应用中具有吸引力。了解TiAl合金的潜在蠕变机理对于其设计，制造和高温应用至关重要。在这里，我们对纳米晶和纳米孪晶中的高温蠕变进行了一系列的大规模原子模拟。$\gamma$-TiAl合金。我们的模拟结果显示了施加的应力，晶粒尺寸和温度对纳米晶和纳米孪晶TiAl合金蠕变行为和机理的影响，这与基于经典Bird-Dorn-Mukherjee方程的预测非常吻合。更有趣的是，我们的模拟结果表明，对于在高外加应力下平均晶粒尺寸为20 nm的纳米孪晶样品，存在一个2.79 nm的临界孪晶厚度，对应于最低的蠕变速率，这归因于蠕变机理的改变。从位错成核和滑移到由于双边界迁移引起的脱缠。我们当前的研究揭示了纳米晶和纳米孪晶TiAl合金的高温蠕变机理，这指导了具有增强的抗蠕变性的TiAl合金的设计和制造。