鈦鋁合金γ/α2界面結(jié)構(gòu)及拉伸變形行為的分子動(dòng)力學(xué)模擬

鈦鋁合金γ/α2界面結(jié)構(gòu)及拉伸變形行為的分子動(dòng)力學(xué)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(jié)構(gòu)的鈦鋁合金高溫性能優(yōu)異，但片層結(jié)構(gòu)具有較強(qiáng)的各向異性，特別是γ/α2界面，從而導(dǎo)致鈦鋁合金的界面結(jié)構(gòu)和疲勞斷裂等力學(xué)行為強(qiáng)烈依賴于片層取向、厚度和厚度比等參數(shù)。本文采用分子動(dòng)力學(xué)方法，通過(guò)考察共格和非共格界面，發(fā)現(xiàn)體系總能量隨兩相厚度比變化，得到兩種界面相互轉(zhuǎn)變的臨界片層厚度；對(duì)不同片層厚度的鈦鋁合金進(jìn)行垂直界面的拉伸加載，共格界面的屈服強(qiáng)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(fā)生在γ相一側(cè)，形成Shockley偏位錯(cuò)，進(jìn)而通過(guò)剪切傳遞方式穿過(guò)γ/α2界面，激活α2相的錐面層錯(cuò)；γ/α2界面為后續(xù)的位錯(cuò)和孿生提供形核點(diǎn)。相關(guān)結(jié)果為鈦鋁合金結(jié)構(gòu)穩(wěn)定性評(píng)價(jià)和性能改善提供了理論基礎(chǔ)。

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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