Coupling of irreversible plastic rearrangements and heterogeneity of the local structure during deformation of metallic glasses

金属玻璃作为结构材料应用的主要困难之一在于它们倾向于局部塑性变形和由此产生的在载荷下的灾难性失效。然而，尽管两者，科学以及应用相关的利益，应变本地化的早期阶段没有得到很好的理解。本项目的目的，因此，在金属玻璃中的剪切局部化的初始阶段的研究。这里的一个重要问题是小规模的结构异质性，固有的无定形固体，和波动的局部应力的发生的基本剪切转换事件所发挥的作用。这些结构-应力效应对于金属玻璃中从均匀塑性变形到剪切带的转变也是非常重要的。以下问题在此具有关键意义。(i)当地的结构和当地的作用应力如何影响不可逆的粒子重排和（ii）在何种条件下，他们可能会导致系统跨越剪切带的形成？为了充分和全面地解决这些问题，本项目汇集了金属玻璃实验研究和模型玻璃体系计算机模拟方面的专业知识。分子动力学模拟，一方面，将提供有关小尺度上的集体粒子重排的详细信息，从而有助于识别基本塑性事件，即所谓的剪切转变区。此外，应力张量将在局部尺度上确定，与基本剪切事件相关。使用由此获得的模拟数据，将在空间和时间上评估应力和塑性应变的相关性。同样，塑性应变和局部结构之间的相互联系的分析将被执行。实验，另一方面，将揭示静态和动态性能的金属玻璃下变形的桥接尺度，从原子的，先进的TEM方法，如电子相关显微镜将解决结构的不均匀性，以介观和宏观尺度，提供样品平均信息的增强原子运输有关的早期阶段的变形本地化，剪切带之前。上述实验和计算机模拟将从不同角度揭示局部结构和应力波动对剪切带形成的作用。目前的合作工作的首要目标在于评估结果的补充实验和理论工作包，以获得物理一致的图片之间的过渡金属玻璃的弹性和塑性。

One of the major difficulties in the applications of metallic glasses as structural materials lies in their propensity to localized plastic deformation and the resulting catastrophic failure under load. Yet, although of both, scientific as well as application related interest, the early stages of strain localization are not well understood. The present project aims, therefore, at a study of the initial stages of shear localization in metallic glasses. An important issue here is the role played by small scale structural heterogeneity, inherent to amorphous solids, and fluctuations of the local stress for the occurrence of an elementary shear transformation event. These structure-stress effects are also of great importance for the onset of the transition from a homogeneous plastic deformation to shear bands in metallic glasses. The following questions are of key interest here. (i) How do the local structure and the locally acting stress influence irreversible particle rearrangements and (ii) under which conditions may they lead to the formation of system-spanning shear bands? In order to address these issues adequately and in a comprehensive way, the present project brings together expertise in experimental investigations of metallic glasses and computer simulations of model glassy systems. Molecular dynamics simulations, on the one hand, will provide detailed information about the collective particle rearrangement on small scales, thereby helping to identify elementary plastic events, the so-called shear transformation zones. Moreover, the stress tensor will be determined on the local scale, relevant for elementary shear events. Using the thus obtained simulated data, correlations of stress and plastic strain will be evaluated both in space and time. Similarly, an analysis of the mutual connection between plastic strain and the local structure will be performed. Experiments, on the other hand, will reveal static and dynamic properties of metallic glasses under deformation on bridging scales, from atomistic ones, on which advanced TEM methods such as electron correlation microscopy will address the structural heterogeneities, to meso- and macroscopic scales, providing sample-averaged information on the enhancement of atomic transport related to earlier stages of deformation localization, prior to shear banding. The above mentioned experiments and computer simulations will shed light from different angles onto the role of the local structure and stress fluctuations for the onset of shear banding. The overarching goal of the present collaborative work lies in assessing the results from the complementing experimental and theoretical work packages to obtain a physically consistent picture of the transition between elasticity and plasticity in metallic glasses.