Investigation of Mechanical Deformation in Small-Scale Metallic Systems: Interfaces and Boundaries in Nano-pillars

技术总结：已经证明，在单晶中，一旦达到微米尺度，屈服（和断裂）强度以幂律的方式随着样本量的减少而增加，因此不能再从体响应或文献中推断出来。虽然这些研究为在小尺度上操作的基本变形过程提供了强大的基础，但它们距离代表结构应用中使用的真实材料还有很长的路要走，这些材料的微观结构通常很复杂，包含边界和界面。尺寸有限的均质界面（即晶粒和孪晶界）和非均质界面（即相和沉淀-基体界面）是影响大多数现代材料结构可靠性的关键因素。它们对损伤起始也特别重要。解决这些问题代表了本研究的重点，实验和计算方法将应用于深入了解小规模金属系统的力学行为和微观结构演变，其变形是由缺陷与界面以及自由表面的复杂相互作用控制的。该提案提出了一个统一的计划，将独特的纳米级样品制造技术与最先进的原位力学测试能力和特定地点的TEM显微镜相结合，并进一步得到计算工作的支持。该项目的目标是发展对包含已知界面及其随后的机械性能的小尺度（亚微米）纳米柱的变形机制的物理理解。将重点研究单个纳米柱中的以下界面：(1)跨越柱体的多个晶界（纳米晶Cu）；(2) Cu中的周期性生长孪晶界（纳米孪晶Cu）；(3)纳米晶粒与纳米孪晶的结合（纳米晶纳米孪晶Cu）。拟议的研究也有望阐明内在和外在长度尺度在金属变形机制中的相对作用，这将通过建筑控制对具有前所未有的机械性能的材料的发展产生变革性影响。非技术概要：结构材料的有用性能通常由其体微观结构决定。几个世纪以来，结构材料的改进在很大程度上依赖于加工，而加工反过来又决定了材料的微观结构和性能。材料科学正在进入一个革命性的时代，在这个时代，不仅通过材料，而且通过对其成分的建筑控制来获得特定的材料特性，通常是亚微米级的。这些新原理的性能是由材料微观结构和结构的结构（而不仅仅是整体性能）的组合决定的，为了将这些新原理应用到结构中，有必要对机械加载时界面上发生的过程进行量化。该提案提出了一个统一的计划，将独特的纳米尺度样品制造技术与最先进的原位机械测试能力和显微镜相结合，并进一步得到计算努力的支持。该项目的目标是发展对具有受控原子排列的小尺度（亚微米）金属纳米柱及其随后的机械性能的变形机制的物理理解。获得的知识对于结构材料的发展和改进至关重要，而在一个令人兴奋的跨学科领域培养研究生和本科生，将材料现象与综合理论和实验研究相结合，将有助于培养新一代的科学家。

TECHNICAL SUMMARY:It has been shown that in single crystals yield (and fracture) strengths increase in a power law fashion with sample size reduction once micron scale is reached, and therefore can no longer be inferred from bulk response or from literature. While these studies provide a powerful foundation for the fundamental deformation processes operating at small scales, they are a far reach from representing real materials used in structural applications, whose microstructure is often complex, containing boundaries and interfaces. Both homogeneous (i.e. grain and twin boundaries) and heterogeneous (i.e. phase and precipitate-matrix boundaries) interfaces in size-limited features are crucial elements in structural reliability of most modern materials. They are also of particular importance to damage initiation. Addressing these issues represents key thrust of this proposed research, where experimental and computational methods will be applied to obtain insight into mechanical behavior and microstructural evolution in small-scale metallic systems, whose deformation is governed by intricate interactions of defects with interfaces as well as with free surfaces. This proposal presents a unified plan combining unique nano-scale sample fabrication techniques with state-of-the-art in-situ mechanical testing capability, and site-specific TEM microscopy, further supported by computational efforts. The objective of this project is to develop a physical understanding of deformation mechanisms operating in small-scale (sub-micron) nano-pillars containing known interfaces and their ensuing mechanical properties. Attention will be focused on studying the following interfaces in individual nano-pillars: (1) multiple grain boundaries spanning the pillar volume (nanocrystalline Cu); (2) periodic in-grown twin boundaries in Cu (nano-twinned Cu); and (3) a combination of nano-grains and nano-twins in Cu (nanocrystalline nano-twinned Cu). Proposed study promises to also shed light on the relative role of intrinsic vs. extrinsic length scales on deformation mechanisms in metals, which will have a transformative impact in development of materials with unprecedented mechanical properties through architectural control.NON-TECHNICAL SUMMARY:Useful properties of structural materials are generally governed by their bulk microstructure. For centuries, improvements in structural materials relied heavily on processing, which in turn, dictated resulting microstructure and properties. As materials sciences are entering a revolutionary era, where specific material properties are attained through not only material but also architecture control of its constituents, often with sub-micron dimensions. In order to utilize these new principles, whose properties are dictated by combination of material microstructure and structure's architecture (rather than by bulk properties only) into structural applications, it is imperative to quantify the processes occurring at the interfaces upon mechanical loading. This proposal presents a unified plan combining unique nano-scale sample fabrication techniques with state-of-the-art in-situ mechanical testing capability, and microscopy, further supported by computational efforts. The objective of this project is to develop a physical understanding of deformation mechanisms operating in small-scale (sub-micron) metallic nano-pillars with controlled atomic arrangements and their ensuing mechanical properties. Gained knowledge promises to be essential for the development and improvement of structural materials, while training graduate and undergraduate students in an exciting interdisciplinary field that combines materials phenomena with integrated theoretical and experimental studies will help train a new generation of scientists.