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

金属玻璃变形过程中不可逆塑性重排与局部结构异质性的耦合

• 批准号: 325408982
• 负责人: Professor Dr. Fathollah Varnik
• 金额: --
• 依托单位: Institut für Materialphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/325408982?language=en
• 关键词: Coupling; irreversible; plastic; rearrangements; heterogeneity

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.

金属玻璃作为结构材料应用的主要困难之一在于其在载荷作用下容易发生局部塑性变形并导致灾难性破坏。然而，尽管科学和应用相关的兴趣，菌株定位的早期阶段还没有很好地理解。因此，本项目旨在研究金属玻璃中剪切局部化的初始阶段。这里的一个重要问题是，在发生基本剪切转变事件时，非晶固体固有的小尺度结构非均质性和局部应力波动所起的作用。这些结构应力效应对于金属玻璃从均匀塑性变形到剪切带转变的开始也非常重要。以下问题在这里很重要。(i)局部结构和局部作用应力如何影响不可逆的颗粒重排，（ii）在哪些条件下它们可能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系统计算机模拟方面的专业知识。一方面，分子动力学模拟将在小尺度上提供关于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，与初级剪切事件有关。利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，塑性应变与局部结构之间的相互关系也将进行分析。另一方面，实验将揭示金属玻璃在桥接尺度下变形的静态和动态特性，从原子尺度，在原子尺度上，先进的TEM方法，如电子相关显微镜将解决结构异质性，到中观和宏观尺度，提供与变形定位早期阶段相关的原子传输增强的样本平均信息，在剪切带之前。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发生的作用。目前合作工作的总体目标在于评估互补的实验和理论工作包的结果，以获得金属玻璃在弹性和塑性之间过渡的物理一致的图像。