Fluctuations of Amorphous Metals in Time and Space from Electron Nanodiffraction

技术概述：用相干探针照射材料时衍射强度的波动包含有关无序材料结构的独特信息。在这个项目中，一个新的，最先进的扫描透射电子显微镜将被用于研究金属玻璃和玻璃形成液体的空间和时间波动，具有纳米空间分辨率。空间波动提供了纳米级结构秩序的信息，这将用于研究一些高铝含量金属玻璃在初晶反应中的成核和生长。通过相变测量原晶团簇的尺寸随时间和温度的变化。时间的波动提供了原子动力学的信息，这些信息将用于研究脆性随温度变化的大块玻璃成形合金的玻璃化转变。特别是，将寻求一些玻璃化转变模型基础上的纳米尺度空间非均质动力域的直接实验证据。对于这两方面的努力，将开发直径为0.1至~ 1000nm的相干电子探针。这些探针也将用于纳米衍射和衍射成像。非技术概要：金属玻璃是一类有潜在用途的新型金属合金。它们具有非凡的强度和弹性，可以作为制造新型纳米结构金属的垫脚石，例如，它们具有更高的强度或有用的磁铁性能。开发这些材料的一个障碍是了解它们的结构，特别是在1纳米左右的长度尺度上，这是一个20-50个原子的簇。该项目支持使用电子显微镜新技术来测量纳米级结构的研究。新的结构数据将用于探索金属玻璃在熔融金属合金冷却过程中是如何形成的，以及金属玻璃用于制造纳米结构金属的方法之一。了解金属玻璃是如何从金属液体中形成的，可能会揭示一般的玻璃化转变，这是材料物理学中的重大挑战之一。该项目还将通过在线实例数据库（http://tem.msae.wisc.edu/emdb/）传播先进的电子显微镜技术，从而提高美国技术人员的竞争力。数据库中的例子用于课堂教学，以及希望提升技能的在职科学家和工程师。

TECHNICAL SUMMARY:Fluctuations in the intensity diffracted from materials illuminated with coherent probes contain unique information about the structure of disordered materials. In this project, a new, state-of-the-art scanning transmission electron microscope will be used to study spatial and temporal fluctuations in metallic glasses and glass forming liquids with nanometer spatial resolution. Fluctuations in space give information about nanoscale structural order, which will be used to study nucleation and growth during the primary crystallization reaction exhibited by some high Al-content metallic glasses. The size distribution of protocrystalline clusters as a function of time and temperature will be measured through the phase transformation. Fluctuations in time give information about atom dynamics, which will be used to study the glass transition of bulk-glass forming alloys with varying fragility as a function of temperature. In particular, direct experimental evidence of the nanoscale spatially heterogeneous dynamical domains that underlie some models of the glass transition will be sought. For both these efforts, coherent electron probes spanning 0.1 to ~1000 nm in diameter will be developed. These probes will also be useful for nanodiffraction and diffractive imaging.NON-TECHNICAL SUMMARY:Metallic glasses are a potentially useful new class of metal alloys. They have exceptional strength and springiness, and they can be used as a stepping stone to create new nanostructured metals with, for example, even higher strength or useful properties as magnets. One of the stumbling blocks to exploiting these materials is understanding their structure, particularly at a length scale around 1 nanometer, which is a cluster of 20-50 atoms. This project supports research using a new technique in electron microscopy to measure that nanometer-scale structure. The new structural data will be used to explore how metallic glasses form in the first place during cooling of a molten metal alloy, and one of the ways metallic glasses can be used to create nanostructured metals. Understanding how metallic glasses form from metallic liquids may shed light on the glass transition in general, which is one of the grand challenges in materials physics. This project will also enhance the competitiveness of the U.S. technical workforce by disseminating advanced electron microscopy techniques through an online database of examples (http://tem.msae.wisc.edu/emdb/). Examples from the database are used in classroom teaching and by working scientists and engineers who want to upgrade their skills.