Fluctuations of Amorphous Metals in Time and Space from Electron Nanodiffraction

技术概述：由相干探头照射的材料的衍射光强度波动包含有关无序材料结构的独特信息。在这个项目中，将使用一种新型的、最先进的扫描电子显微镜来研究纳米空间分辨率的金属玻璃和玻璃形成液体中的空间和时间涨落。空间涨落提供了有关纳米结构有序性的信息，这将被用来研究一些高Al含量的金属玻璃在初级晶化反应中的形核和生长。通过相变测量原晶团簇的尺寸分布随时间和温度的变化。时间涨落提供了有关原子动力学的信息，这些信息将被用来研究随温度变化的脆性大块玻璃形成合金的玻璃转变。特别是，将寻找作为玻璃化转变模型基础的纳米尺度空间不均匀动力学区域的直接实验证据。对于这两项工作，将开发直径从0.1到~1000纳米的相干电子探测器。这些探针还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的有用的新型金属合金。它们具有非凡的强度和弹性，可以作为垫脚石来创造新的纳米结构金属，例如，具有更高的强度或有用的特性，如磁铁。开发这些材料的绊脚石之一是理解它们的结构，特别是在大约1纳米的长度尺度上，这是一个由20-50个原子组成的团簇。该项目支持使用电子显微镜中的新技术来测量纳米级结构的研究。新的结构数据将被用来探索金属玻璃在熔融的金属合金冷却过程中首先是如何形成的，以及金属玻璃可以用来制造纳米结构金属的方法之一。了解金属液体是如何形成金属玻璃的，可能有助于从总体上阐明玻璃转变，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被用于课堂教学，以及想要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.