鈦鋁合金γ/α2界面結構及拉伸變形行為的分子動力學模擬

鈦鋁合金γ/α2界面結構及拉伸變形行為的分子動力學模擬Atomistic simulation of the structure and deformation behavior of γ/α2 interface in TiAl alloys

具有γ-TiAl和α2-Ti3Al兩相片層結構的鈦鋁合金高溫性能優異，但片層結構具有較強的各向異性，特別是γ/α2界面，從而導致鈦鋁合金的界面結構和疲勞斷裂等力學行為強烈依賴于片層取向、厚度和厚度比等參數。本文采用分子動力學方法，通過考察共格和非共格界面，發現體系總能量隨兩相厚度比變化，得到兩種界面相互轉變的臨界片層厚度；對不同片層厚度的鈦鋁合金進行垂直界面的拉伸加載，共格界面的屈服強度高于非共格界面，斷裂行為隨γ和α2相的的厚度比變化。塑性變形首先發生在γ相一側，形成Shockley偏位錯，進而通過剪切傳遞方式穿過γ/α2界面，激活α2相的錐面層錯；γ/α2界面為后續的位錯和孿生提供形核點。相關結果為鈦鋁合金結構穩定性評價和性能改善提供了理論基礎。

TiAl alloys with the γ-TiAl/α2-Ti3Al lamellar structure exhibit excellent high temperature performance. However, the lamellae are strongly anisotropic, in particular the γ/α2 interface, which leads to the strong dependence of the interface structure and mechanical properties, e.g., fatigue and fracture, on lamella orientation, thickness, volume fraction, etc. In the present work, molecular dynamics with the embedded-atom potential is employed to investigate the energy of both the coherent and incoherent γ/α2 interfaces. The interface coherency is found to depend on the thickness ratio of the γ lamellae over the α2 lamellae, resulting in a critical lamella thickness, below/above which the interface is coherent/incoherent; loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of the incoherent interface and the crack nucleation behavior varies with the thickness ratio of the γ lamellae over the α2 lamellae; plastic deformation occurs first in the γ region, forming Shockley partial dislocations and crosses the γ/α2 interface via slip transfer, activating stacking faults on the pyramidal plane in the α2 region; the γ/α2 interface provides nucleation sites for subsequent dislocations and cracks. The present results thus contribute to the evaluation of the structural stability and the improvement of mechanical performance of TiAl alloys.

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