Metallic glasses and strain localization

Megalo项目的重点是金属玻璃的异质塑性变形和均匀塑性变形之间的过渡。到目前为止，人们对这种转变知之甚少，尽管它对基础研究和玻璃应用都有重要的影响。为了处理控制这一过渡的基本机制，制定了一项协调一致的战略，该战略由紧密联系的实验和理论分析组成：将从地方尺度开始，在不同的长度尺度上研究结构异质性及其影响，方法是补充实验技术，从而能够评估具有基本和实际重要性的主要物理参数。这些结果将与理论预测进行比较，这些预测与流变性有关，在整个过渡区和不同长度的尺度上，从离散区到连续区。这一办法依赖并利用了联合体成员的补充专门知识，并应提供一幅支配变形本地化和均质流动之间过渡的机制的实际可靠图景。仅基于一些实验研究，最近文献中的建议将这种转变与依赖于热和时间的结构重排之间的竞争联系起来。这几项专注于特定成分的研究表明，变形模式的剧烈变化将是玻璃内部发生的基本机制发生转变的足迹。预计它将受到不同结构变化的支配，特别是受中期秩序的性质和长度规模及其动态的支配。到目前为止，这方面还没有被理解。Megalo项目的目标是研究这种转变，并确定控制这种转变的一阶特征是什么。为此，选择了两种金属玻璃，它们在金属玻璃的可用范围内表现出关于其脆性的相当明显的特征。将在压缩和拉伸两种情况下进行高温测试，并将特别注意开发适当的数字图像相关(DIC)技术，以解决在扫描电子显微镜环境下作为温度和应变率函数的应变局部化问题。变形的样品将被表征，以识别发生应变局部化的区域和这些区域之外的结构变化。为此，将使用互补的实验技术，即涨落电子显微镜、扩散系数测量和纳米压痕，并通过分子动力学和有限元计算对金属玻璃中的应变局域化进行建模。各参与组的密切合作以及博士生的交流将确保Megalo项目的规模过渡办法取得成功。

The focus of the MEGALO project is set by the transition between heterogeneous and homogeneous plastic deformation of metallic glasses. So far, this transition is poorly understood even though it has important bearings for basic research as well as glass application. In order to address the underlying basic mechanisms that control this transition, a well-concerted strategy has been devised that consists of closely interlinked experimental and theoretical analyses: structural heterogeneities and their impact will be studied on different length scales, starting at the local scale, through complementing experimental techniques, allowing an evaluation of the main physical parameters of fundamental as well as practical importance. These results will be compared with theoretical predictions, in connection with rheological properties all the way through the transition regime and at various length scales, from the discrete to the continuum regime. This approach relies on and exploits the complementing expertise of the members of the consortium and shall provide a physically solid picture of the mechanisms that govern the transition between localization of deformation and homogeneous flow. Based on only a few experimental studies, recent suggestions in the literature linked the transition to the competition between thermal- and time-dependent structural rearrangements. These few studies, focusing on specific compositions, suggest that the drastic change of the deformation mode would be a footprint of a transition in the elementary mechanisms occurring inside the glass. It is expected to be governed by different structural changes and particularly by the nature and the length scale of the medium range order (MRO) as well as its dynamics. So far, this aspect has not yet been understood. It is the aim of MEGALO project to investigate this transition and to identify what are the first order features that control it. For this reason, two metallic glasses are selected that show, within the range available for metallic glasses, rather distinct characteristics concerning their fragility. High temperature testing will be performed in both compression and tension and a particular attention will be paid to develop appropriate Digital Image Correlation (DIC) techniques to tackle strain localisation as a function of temperature and strain rate in SEM environment. The deformed samples will be characterised to identify structural variations between zones where strain localisation occurs and outside these zones. To this end, complementary experimental techniques, namely fluctuation TEM, diffusivity measurements and nanoindentation, will be used in combination with the modelling of strain localisation in metallic glasses via molecular dynamics and finite element calculations. The close collaboration of the participating groups as well as the exchange of PhD students shall ensure the success of the scale-bridging approach of the MEGALO project.