Atomic-Scale Observation of Deformation in Nanoscale Body Center Cubic (BCC) Crystals

纳米级体心立方 (BCC) 晶体变形的原子尺度观测

• 批准号: 1536811
• 负责人: Scott Mao
• 金额: $ 34万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2019-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536811&HistoricalAwards=false
• 关键词: Atomic; Scale; Observation; Deformation; Nanoscale

The metals used in mechanical components for small-scale devices at room temperature are normally of face center cubic character. Their mechanical behavior is generally well-known. However, at high temperature, these FCC metals become soft. Therefore, they are not suitable for high temperature application. In that case, body center cubic (BCC) nanostructured metals offer an alternative. These metals possess potentially desired high temperature strength. They are expected to serve in components in future high temperature device such as micro/nano electro-mechanical systems (MEMS/NMMS). Although the mechanical behavior of large-sized BCC metals is well-known, these macroscale properties cannot be directly used for nanometer-sized structures due to size effects. For the analysis of the small devices, it is necessary to know the mechanical behavior of BCC metals at small scales. However, there is lack of experimental data for the deformation process at small scales, and also there is no understanding of the deformation behavior of BCC metals at the nanometer scale. An in-situ mechanical testing approach inside a special high resolution transmission electron microscope (HRTEM) will be used in this research. This constitutes a new approach for studying the mechanical behavior at atomistic scale for nanometer-sized BCC metal specimens. The understanding of the mechanical behavior of nanometer-sized BCC crystals gained from this research will have direct impact on the design and fabrication of the high temperature MEMS/NEMS. The research on the in-situ HRTEM is expected to open a new approach to directly observe atomic-scaled deformation under mechanical stress. The results from the research are expected to contribute to the advancement of experimental mechanics and nanomaterials. The research will employ an in-situ tensile technique utilizing the most advanced instrument of high resolution transmission electron microscope (HRTEM) to reveal the deformation process in nanometer-sized BCC metal specimens. Firstly, nanometer-sized high strength BCC metal specimens will be fabricated in-situ. Secondly, tensile/compression experiment in-situ in the HRTEM will be conducted on these BCC specimens to documents deformation behavior at room temperature and high temperatures; Thirdly, lattice disturbance, dislocation dipole nucleation and competition between slip and twinning in the deformation process will be observed. Molecular dynamics modeling on key issues with a) dislocation dipole formation; b) nucleation of twinning and dislocation and c) competition of twinning and slip as function of crystal orientation will be carried out. The experiments will be carried out via national user facilities at the Environmental Molecular Sciences Laboratory (EMSL), Pacific Northwest National Laboratory, Richland, WA. This collaboration will build national research infrastructure.

在室温下用于小型设备的机械部件的金属通常是面心立方性质的。它们的力学行为通常是众所周知的。然而，在高温下，这些面心立方金属会变软。因此，它们不适合高温应用。在这种情况下，体心立方(BCC)纳米结构金属提供了另一种选择。这些金属具有潜在的所需高温强度。它们有望用于未来的高温器件，如微/纳米机电系统(MEMS/NMMS)。虽然大尺寸体心立方金属的力学行为是众所周知的，但由于尺寸效应，这些宏观性能不能直接用于纳米结构。对于小型器件的分析，有必要了解体心立方金属在小尺度下的力学行为。然而，目前还缺乏关于小尺度变形过程的实验数据，也没有对体心立方金属在纳米尺度上的变形行为的了解。在这项研究中将使用一种特殊的高分辨率电子显微镜(HRTEM)内的原位力学测试方法。这为研究纳米体心立方金属试件的原子级力学行为提供了一条新的途径。对纳米体心立方晶体力学行为的了解将对高温MEMS/NEMS的设计和制造产生直接影响。原位高分辨电子显微镜的研究有望为直接观测机械应力作用下原子尺度的变形开辟一条新途径。这一研究成果有望为实验力学和纳米材料的发展做出贡献。这项研究将利用最先进的高分辨率电子显微镜(HRTEM)的原位拉伸技术来揭示纳米级体心立方金属试件的变形过程。首先，将原位制备纳米尺寸的高强度体心立方金属试件。其次，对这些体心立方试件进行原位拉伸/压缩实验，以记录其在室温和高温下的变形行为；第三，观察到变形过程中的晶格扰动、位错偶极子形核以及滑移和孪生之间的竞争。对a)位错偶极形成，b)孪晶和位错成核，c)孪晶和滑移竞争作为晶体取向函数的关键问题进行了分子动力学模拟。这些实验将通过华盛顿州里奇兰太平洋西北国家实验室的环境分子科学实验室(EMSL)的国家用户设施进行。这一合作将建立国家研究基础设施。