Fluctuations of Amorphous Metals in Time and Space from Electron Nanodiffraction

技术概要：用相干探针照射的材料衍射的强度波动包含了关于无序材料结构的独特信息。在这个项目中，一个新的，国家的最先进的扫描透射电子显微镜将用于研究空间和时间波动的金属玻璃和玻璃形成液体与纳米空间分辨率。在空间中的波动给出了有关纳米结构的顺序，这将被用来研究一些高铝含量的金属玻璃所表现出的初级结晶反应过程中的成核和生长的信息。通过相变测量了原始晶粒的尺寸分布随时间和温度的变化。时间的波动给出了原子动力学的信息，这将被用来研究块体玻璃形成合金的玻璃化转变，其脆性随温度的变化而变化。特别是，直接的实验证据的纳米级空间异质动态域的基础上的一些模型的玻璃化转变将寻求。对于这两项工作，将开发直径为0.1至~1000 nm的相干电子探针。这些探针也将用于纳米衍射和衍射成像。非技术摘要：金属玻璃是一种潜在有用的新型金属合金。它们具有特殊的强度和弹性，可以用作制造新的纳米结构金属的垫脚石，例如，具有更高的强度或有用的磁性。开发这些材料的绊脚石之一是了解它们的结构，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首先是如何形成的，以及金属玻璃可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，这是材料物理学的重大挑战之一。该项目还将通过一个在线实例数据库（http：//tem.msae.wisc.edu/emdb/）传播先进的电子显微镜技术，提高美国技术人员的竞争力。数据库中的示例用于课堂教学，并由希望提升技能的科学家和工程师使用。

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.