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: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=682890
• 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.**

在过去的四十年中，金属玻璃（MGS）或液体金属表现出高强度，较大的弹性极限和在超冷液体区域的独特形成能力。但是，在低温较低的低温区域，MGS的塑性变形位于所谓的剪切带狭窄区域内，导致灾难性衰竭，并限制了MGS及其应用的结构可靠性。当前对MGS塑性变形的理解是，可塑性是由剪切转化区（STZ）携带的，这是一种类似于晶体金属中的位错。这些STZ是原子簇，它们会从其平均位置进行集体洗牌/位移，以适应应变并放松所施加的应力。尽管关于STZ大小的发表文献达成共识仍然值得商bat，但人们普遍认为，在原子包装效率较低的地区，STZ被激活。但是，尚不清楚变形定位是如何从STZ演变而来的。我们最近对模型CU-ZR MGS系统之间关系的研究表明，这些复杂液体的动力学可以以“动态异质性”（大型的空间相关迁移率波动）形式，其形式是由高度移动原子的瞬态簇形式的形式，这些原子由弦乐原子的高度合作运动组成，可以通过该系统的平均数量和动力学的数量组成。显然，弦样合作运动与STZ之间存在密切的联系，这在MGS中的塑性变形中起着至关重要的作用。在当前的研究中，我们建议使用分子动力学仿真方法来揭示合作弦样原子运动对金属玻璃变形行为的作用。特别是，我们将解决诸如字符串与STZ之间的确切关系等问题？在剪切带的形成过程中，弦如何发展？剪切带宽度与弦长相关吗？一个人可以修改字符串长度，以便可以控制剪切带的形成吗？通过这项研究的成功完成，它将更好地了解MGS的塑性变形，并提供指导以从基本和技术的观点均提高MG的可塑性。**