Collaborative Research: Investigation of Deformation Mechanisms Governing the Tensile Ductility of Twinned Metal Nanowires

合作研究：控制孪晶金属纳米线拉伸延展性的变形机制的研究

• 批准号: 1410331
• 负责人: Ting Zhu
• 金额: $ 21万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1410331&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigation; Deformation; Mechanisms

Non-technical summaryRapid progress in nanotechnology is currently under way in that small structures and devices are being fabricated at the micrometer to nanometer scales. The reliable design of these structures and devices calls for an understanding of the mechanical properties of materials at small length scales. Metallic nanostructures like nanowires have been shown to exhibit ultra-high yield strength, on the order of one tenth of their elastic moduli. However, these metallic nanostructures usually have limited hardening, causing low tensile strain to failure. Such low ductility can severely affect the mechanical integrity of the constituent nanostructures in nanomechanical devices and other technological applications. There is currently a critical need to understand the fundamental deformation mechanisms governing the strain hardening and tensile ductility in metallic nanostructures. The proposed research synergistically integrates the in situ nanomechanical experiment and computational modeling to investigate the nearly unexplored strain hardening behaviors in metallic nanostructures. The results are expected to advance our fundamental understanding of deformation mechanisms governing the tensile ductility in metal nanowires and provide a mechanistic basis for the design of strong and ductile metallic nanostructures. Undergraduates will be recruited for summer research on this project. Collaborative research between the graduate students working on this project in Georgia Institute of Technology and North Carolina State University will promote their scientific exchange, increase team-work experience, and develop interdisciplinary expertise.Technical summaryThe metallic nanostructures such as nanowires usually exhibit ultra-high strength, but low tensile ductility, owing to their limited strain hardening capability. The objective of this proposal is to elucidate the deformation mechanisms governing the strain hardening and tensile ductility of an interesting type of metallic nanostructures - five-fold twinned Ag nanowires - which exhibit significant strain hardening in our preliminary experimental measurements. The proposed research involves three thrusts: (i) to perform the in situ nanomechanical testing to measure the tensile stress-strain responses and mechanical properties of individual nanowires; (ii) to perform the transmission electron microscopy characterization of pristine and deformed nanowires for investigation of the underlying dislocation mechanisms and particularly the effects of surface and twin boundary mediated defects; (iii) to conduct the molecular dynamics and transition state theory based atomistic modeling to elucidate dislocation mechanisms that control the strain rate and temperature effects on strain hardening and tensile ductility. The five-fold twinned nanowires studied in this project are different from the single-crystal nanowires, bulk nanocrystalline and nanotwinned metals in that the synergetic effects of free surfaces and coherent internal interfaces (i.e., twin boundaries with unique orientation parallel to the nanowire axis) can be critically important for controlling the dislocation mechanisms of hardening and related mechanical properties. The mechanistic insights gained from this project will be valuable to develop means to enhance the strength without a severe loss of ductility in a range of small-volume metallic materials.

纳米技术中的非技术总结进展目前正在进行中，在小型结构和设备处于微米为纳米尺度的小结构和设备。这些结构和设备的可靠设计要求了解材料在小长度尺度下的机械性能。已经证明，金属纳米结构（如纳米线）在其弹性模量的十分之一的范围内表现出超高的屈服强度。但是，这些金属纳米结构通常的硬化有限，导致低拉伸应变破坏。如此低的延展性会严重影响纳米力学设备和其他技术应用中组成纳米结构的机械完整性。目前，需要了解管理金属纳米结构中应变硬化和拉伸延展性的基本变形机制。提出的研究协同整合了原位纳米力学实验和计算建模，以研究金属纳米结构中几乎未开发的应变硬化行为。预计结果将提高我们对金属纳米线中拉伸延展性的变形机制的基本理解，并为设计强和延性金属纳米结构设计提供了机械基础。本科生将被招募参加该项目的夏季研究。在佐治亚理工学院和北卡罗来纳州立大学从事该项目的研究生之间的合作研究将促进其科学交流，增加团队工作经验并发展跨学科专业知识。技术总结金属纳米结构（例如纳米线），例如纳米线，通常具有超高的强度，但表现出极低的强度，但较低的紧张型耐有限量的良好性，可加强限制性的效果。该提案的目的是阐明一种有趣的金属纳米结构的应变硬化和拉伸延展性的变形机制 - 五倍的双胞胎Ag纳米线 - 在我们的前实验测量中表现出明显的应变硬化。提出的研究涉及三个推力：（i）执行原位纳米力学测试以测量单个纳米线的拉伸应力应变响应和机械性能； （ii）执行原始和变形纳米线的透射电子显微镜表征，以研究潜在的脱位机制，尤其是表面和双边界介导的缺陷的影响； （iii）基于基于原子建模进行分子动力学和过渡状态理论，以阐明脱位机制，以控制应变速率和温度对应变硬化和拉伸延展性的影响。该项目中研究的五倍的双纳米线不同于单晶纳米线，散装纳米晶体和纳米含量的金属，因为自由表面和相干内部接口的协同效应和连贯的内部接口的协同效应（即具有与纳米轴的独特偏置的跨度范围）的相关机制（即，都可以散布的机制）机械性能。从该项目中获得的机械洞察力对于开发手段以增强强度而不会在一系列小体积金属材料中严重损失延展性。