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: 1410475
• 负责人: Yong Zhu
• 金额: $ 21万
• 依托单位: North Carolina State University
• 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=1410475&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.

非技术摘要纳米技术目前正在快速进展，在微米到纳米尺度上制造小型结构和设备。这些结构和设备的可靠设计需要了解小长度尺度下材料的机械性能。纳米线等金属纳米结构已被证明具有超高屈服强度，约为其弹性模量的十分之一。然而，这些金属纳米结构通常具有有限的硬化，导致低拉伸应变失效。如此低的延展性会严重影响纳米机械装置和其他技术应用中纳米结构组成部分的机械完整性。目前迫切需要了解控制金属纳米结构应变硬化和拉伸延展性的基本变形机制。该研究协同整合了原位纳米力学实验和计算模型，以研究金属纳米结构中几乎未被探索的应变硬化行为。这些结果预计将增进我们对控制金属纳米线拉伸延展性的变形机制的基本理解，并为设计坚固且延展性的金属纳米结构提供机械基础。将招募本科生进行该项目的夏季研究。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他们的科学交流，增加团队合作经验，并发展跨学科专业知识。技术摘要纳米线等金属纳米结构由于应变硬化能力有限，通常表现出超高强度，但拉伸延展性较低。该提案的目的是阐明控制一种有趣类型的金属纳米结构（五重孪生银纳米线）的应变硬化和拉伸延展性的变形机制，该金属纳米结构在我们的初步实验测量中表现出显着的应变硬化。拟议的研究涉及三个重点：（i）进行原位纳米力学测试，以测量单根纳米线的拉伸应力应变响应和机械性能； (ii) 对原始和变形纳米线进行透射电子显微镜表征，以研究潜在的位错机制，特别是表面和孪晶边界介导的缺陷的影响； (iii) 进行基于分子动力学和过渡态理论的原子建模，以阐明控制应变速率和温度对应变硬化和拉伸延展性影响的位错机制。本项目研究的五重孪晶纳米线不同于单晶纳米线、块体纳米晶和纳米孪晶金属，因为自由表面和相干内部界面（即具有平行于纳米线轴的独特取向的孪晶边界）的协同效应对于控制硬化和相关的位错机制至关重要。 机械性能。从该项目中获得的机械见解对于开发增强强度而不严重损失一系列小体积金属材料延展性的方法非常有价值。