单晶γ-钛铝沿不同晶向裂纹扩展的分子动力学研究

The molecular dynamics research of single crystal γ-TiAl alloy to crack propagation along the different crystalline phases

摘要:

本文从微观结构上研究了不同晶向下单晶γ-TiAl合金中微裂纹扩展过程及断裂机理。利用分子动力学方法模拟单晶γ-TiAl合金中[100]、[110]及[111]晶向下预置微裂纹的扩展过程。研究表明：[100]晶向的裂纹启裂应力值最小,裂纹强度最低,以脆性解理形式扩展,扩展过程中应力始终集中在裂尖上,该体系应力随时间的增大而减小；[111]晶向裂纹启裂应力值最大,裂纹强度最大,最难扩展,裂纹扩展过程表现出明显取向效应,微裂纹通过裂尖发射滑移位错及裂尖上形成的孪晶进行扩展,扩展过程中应力分布主要集中于裂尖和孪晶面上,且随时间的增大而减小；[110]晶向的微裂纹启裂应力值介于其它两个晶向之间,扩展初期为解理扩展,扩展到一定时间后裂尖原子出现混乱,之后裂尖发射位错使得裂尖钝化,随着加载继续,钝化裂尖的一端再次尖锐并且萌生与主裂纹不在一个平面上的子裂纹,最后主子裂纹相连形成呈台阶状扩展的微裂纹,扩展过程表现出一定取向效应,应力始终集中在裂尖上,并随时间的增大而减小。不同晶向对微裂纹扩展有很大影响。

Abstract:

The micro crack propagation process and the fracture propagation mechanism of the single crystal γ-TiAl alloy of different crystallographic orientation on the microstructure has been studied. The prefabricated micro crack propagation process was simulated of three different crack crystallographic orientations of [100]、[110]and[111] for the single crystal γ-TiAl alloy by the molecular dynamics method. It showed that: The crack stress value is the minimum of [100] crystal orientation, and the crack intensity is the lowest so that it is easy to extend in the form of brittle cleavage extension. The stress has always focused on the crack tip in the process of the extension,and the system of stress decreasesed with time increased,The crack stress value of the [111] orientation is the largest. And the larger the crack strength, the more difficult to extend. The crack propagation process showed the obvious orientation effect. The micro crack extended by the way of crack tip slip dislocation and twin slip was formed on the crack tip. The stress distribution mainly focused on the crack tip and twinning plane in the process of extension, and decreased with time increased. The crack stress value of [110] orientation between two other crystallographic orientations,The Early extension is brittle cleavage extension and the crack tip atoms into chaos after expanded to a certain time and after the crack tip launch dislocation makes the crack tip passivation .As load continued, one the end of passivation crack tip sharp again and sub crack initiation which is not a flat surface with the main crack. At last,the main crack and the sub crack connected to form the micro cracks of step extension. The extension process showed some effect of orientation. The stress always focused on the crack tip, and decreased with time increased. The different crystallographic orientation has great influence to the micro crack propagation.