Ti-Al合金γ/α_2界面结构及拉伸变形行为的分子动力学模拟

Molecular Dynamics Simulation of the Structure and Deformation Behavior of γ/α_2 Interface in TiAl Alloys

采用分子动力学方法,通过考察共格和半共格界面,发现体系总能量随两相厚度比变化,得到2种界面相互转变的临界片层厚度;对不同片层厚度的Ti-Al合金进行垂直界面的拉伸加载,发现共格界面的屈服强度高于半共格界面,断裂行为随γ和α_2相的厚度比变化。塑性变形首先发生在γ相一侧,形成Shockley偏位错,进而通过剪切传递方式穿过γ/α_2界面,激活a2相的锥面层错;γ/α_2界面为后续的位错和孪生提供形核点。

Ti Al alloys with g-TiAl and α2-Ti3Al dual-phase lamellar structure possess not only excellent high temperature performance but also density only about half of traditional superalloys. Such lamellar structure largely determines the mechanical properties of TiAl alloys. However, there is still a lack of understanding on the atomic structure of lamella, as well as their influence on the mechanical behaviors.For this reason, molecular dynamics with an embedded-atom potential is employed to investigate the energies of both the coherent and semi-coherent γ/α2 interfaces. The interface coherency is found to depend on the thickness ratio of γ lamellae to α2 lamellae, and there exists a critical lamella thickness, below/above which the interface is coherent/semi-coherent. Tensile loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of semi-coherent interface and the crack nucleation behavior varies with the thickness ratio of g lamellae to α2 lamellae. The plastic deformation occurs first in the γ region, forming Shockley partial dislocations and then crosses the γ/α2 interface via slip transfer, activating stacking faults on the pyramidal plane in the α2 region. In this process, the γ/α2 interface provides nucleation sites for subsequent dislocations and cracks.