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

技术摘要：已经证明，在单晶中，屈服(和断裂)强度随着样品尺寸的减小而以幂规律的方式增加，一旦达到微米级，就不能再从整体响应或从文献中推断。虽然这些研究为在小范围内运行的基本变形过程提供了强大的基础，但它们远远不能代表结构应用中使用的真实材料，其微观结构通常是复杂的，包含边界和界面。具有尺寸受限特征的均匀界面(即晶界和孪晶界)和非均质界面(即相界面和沉淀-基质界面)都是大多数现代材料结构可靠性的关键要素。它们对破坏的启动也特别重要。解决这些问题是这项拟议研究的关键，其中将应用实验和计算方法来深入了解小规模金属系统的力学行为和微观结构演变，其变形由缺陷与界面和自由表面的复杂相互作用控制。这项建议提出了一个统一的计划，将独特的纳米级样品制作技术与最先进的原位机械测试能力和现场特定的透射电子显微镜相结合，并得到计算工作的进一步支持。该项目的目的是对含有已知界面的小尺度(亚微米)纳米支柱中的变形机制及其随后的机械性能有一个物理上的了解。将重点研究单个纳米柱中的下列界面：(1)跨越柱体体积的多个晶界(纳米晶铜)；(2)铜中周期性的内生孪晶界面(纳米孪晶铜)；以及(3)铜中纳米晶和纳米孪晶的组合(纳米晶纳米孪晶铜)。提出的研究还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，这将通过结构控制对具有前所未有的力学性能的材料的发展产生革命性的影响。非技术摘要：结构材料的有用性能通常由其整体微观结构决定。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最终的微观结构和性能。材料科学正在进入一个革命性的时代，在这个时代，特定的材料特性不仅通过材料，而且通过结构控制其成分，通常是亚微米尺寸。为了将这些由材料微结构和结构结构(而不仅仅是整体性能)共同决定其性能的新原理应用到结构应用中，有必要对机械加载时在界面处发生的过程进行量化。这项建议提出了一个统一的计划，将独特的纳米级样品制作技术与最先进的原位机械测试能力和显微镜相结合，并进一步得到计算工作的支持。该项目的目的是对具有受控原子排列的小尺度(亚微米)金属纳米柱中的变形机制及其随之而来的机械性能有一个物理上的了解。所获得的知识有望对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训研究生和本科生将有助于培养新一代科学家。

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.