Experimental Characterization of Gold Single Crystals and Bicrystals at the Nanoscale with Emphasis on Interaction Between Dislocations and Grain Boundaries

纳米级金单晶和双晶的实验表征，重点是位错和晶界之间的相互作用

• 批准号: 0706058
• 负责人: Jeffrey Kysar
• 金额: $ 40万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0706058&HistoricalAwards=false
• 关键词: Experimental; Characterization; Gold; Single; Crystals

TECHNICAL: Multiscale simulations of dislocation-mediated plasticity with a truly predictive capability have the potential to dramatically reduce the development time of new alloys as well as to enhance the reliability of components made from existing and new alloys. If, however, the potential of the multiscale simulations are ever to be achieved, they must be validated against experiment at all the pertinent length scales. The most difficult length scales at which to perform experiments are the atomic and nanometer length scales simply because of the small magnitude of the quantities involved. It is precisely the experiments at the smallest length scales which are the most important because the ramifications of the phenomena at the smaller length scales cascade out to all larger length scales. The thrust of this transformative project is to perform a definitive set of experiments at the nanometer length scale which can serve as a baseline for critical evaluation and validation of numerical simulations at the nanometer length scale. The PI has developed methods and techniques to fabricate free-standing nanoscale single crystals and bicrystals of gold which have a well-defined crystallographic orientation as well as a well-defined geometry and size (100 nm by 250 nm by 7000 nm). The mechanical properties of the free-standing specimens were probed by deflecting the specimens using a nano-indenter. A continuum analysis of the resulting force-displacement data suggests that the yield strength can be as high as several hundred MPa, and that slip localization by avalanches of dislocations are common in specimens at this small length scale. PI will extend these studies so that it is possible to quantitatively characterize the deformation of single crystals and bicrystals with nanoscale dimensions in terms of the discrete dislocation activity within the specimens. This will be done by developing a MEMS-based actuator to load the nanoscale specimens in uniaxial tension. Detailed characterization will be done by scanning electron microscopy and also transmission electron microscopy in situ during loading. This will give the opportunity to shed insight into the predominance of bulk, grain boundary or surface dislocations sources at that length scale. In addition the detailed interaction of dislocations in nanoscale specimens can be investigated under carefully controlled conditions. Also of critical importance, the conditions for the transmission or non-transmission of dislocations through grain boundaries can be probed as well. The Intellectual Merit of the project is that the ability to bridge the gap between experiment and theory/simulation at the nanoscale would allow for direct validation of concepts and models at the smallest length scales of multiscale models. The enhanced robustness of the models would then cascade out to the larger length scales. Some of the specific items of interest include the determination of location of dislocation sources in nanoscale components, the detailed interaction between dislocations, as well as the detailed interactions of grain boundaries and dislocations. NON-TECHNICAL: One of the main Broader Impacts of this work would include validated physics-based material models which have a true predictive capability. This would significantly shorten the product development of new metal alloys with enhanced strength and toughness. Several undergraduates and at least one graduate student would gain important experience in nanoscale research and technology. An outreach program through the NSF Research Experience for Teachers (RET) program will be established with the science department of a public New York City high school. There will be broad dissemination of the results though peer-judged publication as well as scientific conferences.

技术支持：具有真正预测能力的位错介导塑性的多尺度模拟有可能大大缩短新合金的开发时间，并提高由现有合金和新合金制成的部件的可靠性。然而，如果要实现多尺度模拟的潜力，就必须在所有相关的长度尺度上对实验进行验证。最难进行实验的长度尺度是原子和纳米尺度，因为所涉及的量很小。正是在最小尺度上的实验才是最重要的，因为在较小尺度上的现象的分支会级联到所有较大尺度上。这个变革性项目的主旨是在纳米长度尺度上进行一系列确定的实验，这些实验可以作为纳米长度尺度上数值模拟的关键评估和验证的基线。PI开发了制造独立纳米级单晶和双晶金的方法和技术，这些单晶和双晶具有明确的晶体取向以及明确的几何形状和尺寸（100 nm × 250 nm × 7000 nm）。独立的标本的机械性能进行了探测，通过偏转使用纳米压头的标本。所得到的力-位移数据的连续分析表明，屈服强度可以高达几百MPa，和滑移本地化的位错雪崩是常见的标本在这个小的长度尺度。PI将扩展这些研究，以便可以定量表征单晶和双晶的变形与纳米尺度的离散位错活动的试样内。这将通过开发基于MEMS的致动器来实现，以在单轴张力下加载纳米级试样。将通过扫描电子显微镜和加载期间原位透射电子显微镜进行详细表征。这将使我们有机会深入了解在该长度尺度下，体位错、晶界位错或表面位错源的优势。此外，可以在仔细控制的条件下研究纳米级样品中位错的详细相互作用。同样至关重要的是，位错通过晶界的传输或不传输的条件也可以被探测到。该项目的智力优势是，能够弥合实验和理论/模拟之间的差距差距在纳米尺度将允许直接验证的概念和模型在最小的长度尺度的多尺度模型。模型的增强的鲁棒性随后将级联到更大的长度尺度。感兴趣的一些具体项目包括确定纳米级组件中位错源的位置，位错之间的详细相互作用，以及晶界和位错的详细相互作用。非技术性：这项工作的主要影响之一将包括经过验证的基于物理的材料模型，这些模型具有真正的预测能力。这将大大缩短具有增强强度和韧性的新金属合金的产品开发。几个本科生和至少一个研究生将获得纳米研究和技术的重要经验。将与纽约市一所公立高中的科学系一起，通过NSF教师研究经验（RET）计划建立一个外展计划。将通过同行评审出版物和科学会议广泛传播研究结果。