The Role of Cooperative Atomic Motion in the Plastic Deformation of Metallic Glasses

原子协同运动在金属玻璃塑性变形中的作用

• 批准号: RGPIN-2017-03814
• 负责人: Zhang, Hao
• 金额: $ 2.04万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=669660
• 关键词: Role; Cooperative; Atomic; Motion; Plastic

Metallic glasses (MGs) or liquid metals, exhibiting high strength, large elastic limit, and unique forming capability in the supercooled liquid region, have been extensively studied in the last four decades. However, at low temperature region that is well below the glass-transition temperature, plastic deformation of MGs is highly localized within a so-called shear band narrow region, resulting in catastrophic failure and limiting the structural reliability of MGs and their applications. Current understanding of plastic deformation of MGs is that the plasticity is carried by the shear transformation zones (STZs), an analogous to dislocations in crystalline metals. These STZs are clusters of atoms that undergo collective shuffle/displacement from their mean positions, so as to accommodate strain and to relax the applied stress. While consensus in published literature on the size of the STZs is still debatable, it is generally agreed that the STZs get activated in the regions where the atomic packing is less efficient. However, it remains unclear as to how the deformation localization evolves from STZs. Our recent study of the relationship between structure and dynamics of a model Cu-Zr MGs system reveals that the dynamics of these complex liquids can be characterized by “dynamic heterogeneity” (large spatially correlated mobility fluctuations) in the form of transient clusters of highly mobile atoms that are composed of string-like cooperative motion and the dynamics of the system can be quantitatively described by the average length of the string. Apparently, there is a close connection between string-like cooperative motion and STZ, which plays crucial role in the plastic deformation in MGs. In current research, we propose to use molecular dynamics simulation method to reveal the role of cooperative string-like atomic motion on the deformation behavior of metallic glasses. In particular, we will address questions such as what is the exact relationship between strings and STZs? How do strings evolve during the formation of shear band? Is the shear band width correlated with the string length? Can one modify the string length so that the formation of shear band can be controlled? With a successful completion of this research, it will provide better understanding of the plastic deformation of MGs and provide guidance to improve the plasticity of MGs from both fundamental and technical points of view.**

金属玻璃（MG）或液态金属，表现出高强度，大的弹性极限，和独特的形成能力，在过去的四十年中，已被广泛研究的过冷液体区域。然而，在远低于玻璃化转变温度的低温区域，镁合金的塑性变形高度局限于所谓的剪切带狭窄区域内，导致灾难性失效，限制了镁合金的结构可靠性及其应用。目前对镁合金塑性变形的理解是，塑性是由剪切转变区（STZ）承载的，类似于晶体金属中的位错。这些STZ是从其平均位置经历集体洗牌/位移的原子簇，以便适应应变并放松施加的应力。虽然在已发表的文献中关于STZ的大小的共识仍然是有争议的，但人们普遍认为STZ在原子堆积效率较低的区域被激活。然而，它仍然不清楚如何变形本地化从STZ演变。我们最近的研究模型Cu-Zr MGs系统的结构和动力学之间的关系表明，这些复杂的液体的动力学可以表征为“动态异质性”（大的空间相关的迁移率波动）的形式的瞬态集群的高度移动的原子组成的合作运动的字符串和系统的动力学可以定量描述的平均长度的字符串。显然，类弦协同运动与STZ之间存在着密切的联系，STZ在MG的塑性变形中起着至关重要的作用。在当前的研究中，我们提出用分子动力学模拟方法来揭示类弦原子的协同运动对金属玻璃形变行为的作用。特别是，我们将解决这样的问题，如字符串和STZ之间的确切关系是什么？在剪切带形成过程中弦是如何演化的？剪切带宽度是否与弦的长度相关？是否可以改变弦的长度，从而控制剪切带的形成？随着这项研究的成功完成，它将提供更好地了解镁合金的塑性变形，并从基础和技术角度为提高镁合金的塑性提供指导。