Molecular dynamics simulations to identify atomistic deformationmechanisms in two-phase lamellar TiAl alloys

现代结构材料通常表现出层次化的微观结构，因此在不同的长度尺度上相互依赖的变形机制决定了宏观行为。使用具有代表性的体积元素的计算材料模型或适当的均匀化方法，我们可以确定主导这种变形行为的相关微观结构参数。然而，很多时候，对最小长度尺度上的缺陷-微结构相互作用的理解是缺失的。这种理解对于有目的地改进连续介质模型和系统地优化微观结构是至关重要的。在这方面，最重要的是确定位错运动和孪生等不同过程的重要性以及它们发生的条件。这些条件可以在原子模拟中系统地改变，并可以分析产生的过程。在手头的项目中，用分子动力学模拟研究了两相TiAl合金中片层组织的变形和断裂。TiAl合金的强度和变形性比可以通过创造片层组织来优化。除了颗粒尺寸外，它们还具有额外的微观结构参数，如颗粒内α-2片层的间距、α-2片层之间的伽马片厚度以及某些伽马-伽马界面(伪孪晶、旋转边界、真孪晶)的序列和频率。所有这些参数都有助于限制位错的运动，分别形成孪晶，但其方式仍未解决。在实验上，观察到了霍尔-佩奇强化行为。在这个项目中，它的有效性范围和各个微观结构参数对它的影响方式将被阐明。多相纳米结构合金的强度和韧性是由长度尺度决定的，孪晶形成和位错运动的临界值是控制孪晶形成和位错运动的临界值，这些问题对于建立多尺度的分层组织形变和断裂模型具有普遍意义。

Modern structural materials usually display a hierarchical microstructure, and hence interdependent deformation mechanisms on different length-scales, which determine the macroscopic behaviour. Using computational material models with representative volume elements or suitable homogenisation methods, we can identify the relevant microstructural parameters that dominate this deformation behaviour. However, very often the understanding of defect-microstructure interactions on the smallest length scale is missing. This understanding is crucial for a purposeful improvement of continuum models and a systematic optimisation of the microstructure. Of highest importance in this context is to determine the significance of different processes such as dislocation motion and twinning and the conditions under which they occur. These conditions can be varied systematically within atomistic simulations, and the resulting processes can be analysed.In the project at hand deformation and fracture of lamellar microstructures in two-phase TiAl alloys is investigated using molecular dynamics simulations. The ratio ofstrength and deformability of TiAl alloys can be optimized by creating lamellar microstructures. They are characterised by additional microstructural parameters besides the grain size, such as the spacing of alpha-2 lamellae within the grains, the thickness of the gamma-lamellae between the alpha-2 lamellae, and the sequence and frequency of certain gamma-gamma interfaces (pseudo-twin, rotational boundary, true twin). All these parameters contribute to the confinement of dislocation motion, respectively twin formation, in a manner which is still unresolved. Experimentally, a Hall-Petch-type strengthening behaviour is observed. In this project its range of validity and the way in which the individual microstructural parameters contribute to it, will be clarified. The questions, which length- scale in a multiphase, nano-structured alloy dominates the strength and toughness, and which critical values control twin formation and dislocation motion, are of general importance for formulating quantitative multiscale models of deformation and fracture in hierarchical microstructures.