EAGER: Stability and Nanocrystallization Kinetics of Amorphous Al Alloys

技术概述：块体纳米结构合金的一种重要形式是基于纳米晶体在非晶态基质中的高密度分散。从非晶态基质晶化是一种优选的合成方法，以便允许控制和裁剪微结构，从而实现诸如高强度等性能的控制。由于强度依赖于颗粒尺寸和体积分数，了解和控制数密度为1021？1023m-3的初生铝纳米晶在非晶态基质中的形成机制具有特殊的意义。虽然这种微结构设计的技术意义是明确的，但对于纳米晶体的早期演化，对控制形核和生长动力学的基本理解还没有解决。此外，最近的纳米结构分析表明，非晶相中的原子排列在空间上是不均匀的，因此需要一个新的模型来解释空间非均匀的动力学效应。为了检验未经证实的动力学分析的真实性，我们将系统地研究微量合金化的Al-Y-Fe非晶态合金中的纳米晶形核和结构表征。一个成功的项目的一个重要成果将是形成一种新的范式，用于在非均质材料中合成纳米级微结构的动力学分析。非技术摘要：在块状非晶合金的初级晶化过程中演变出的纳米级微结构是导致具有诱人的结构和功能材料性能的原因，这些材料在交通和通信方面具有技术应用。为了发展纳米尺度的微结构，必须了解控制反应动力学，以便最大化纳米晶的数密度，限制纳米晶的生长。以前的动力学模型认为非晶相在原子尺度上是均匀的，但最近的结构分析揭示了原子尺度的空间不均一性。将开发一种新的动力学分析来处理非晶态Al-Y-Fe合金的空间非均质态，并用纳米晶成核测量进行测试。这一结果与许多金属玻璃中常见的非玻璃化反应--初级晶化的性质有更广泛的关联。该项目努力的一个重要组成部分将是研究生的教育和本科生和高中生的研究经验。此外，有关纳米结构材料的讲座演示将被纳入针对高中生和即将入学的本科生的校园推广计划。

TECHNICAL SUMMARY: An important form of bulk nanostructured alloys is based upon a high density dispersion of nanocrystals in an amorphous matrix. Crystallization from an amorphous matrix is a preferred synthesis method in order to allow the control and tailoring of the microstructure and therefore properties such as high strength. Since the strength depends on the particle size and volume fraction, understanding and controlling the mechanisms of primary aluminum nanocrystal formation with number densities of 1021 ? 1023 m-3 dispersed in an amorphous matrix are of special interest. While the technological significance of this microstructure design is clear, the fundamental understanding of the controlling nucleation and growth kinetics has not been resolved for the early stage evolution of nanocrystals. Moreover, recent nanoscale structural analysis has revealed that the atomic arrangements in the amorphous phase are spatially heterogeneous so that a new model that will be advanced in this study is required to account for the kinetic effects of spatial heterogeneities. In order to provide the database to test the fidelity of the unproven kinetics analysis, nanocrystal nucleation and structural characterization will be studied systematically in Al-Y-Fe amorphous alloys with minor alloying. An important outcome from a successful project will be the formulation of a new paradigm for the kinetics analysis of nanoscale microstructure synthesis in heterogeneous materials.NON-TECHNICAL SUMMARY: The nanoscale microstructures that evolve during primary crystallization of amorphous alloys in bulk volumes are responsible for the attractive structural and functional materials properties that have technological applications in transportation and communications. In order to develop nanoscale microstructures it is essential to understand the controlling reaction kinetics so that the nanocrystal number density is maximized and the growth is limited. Previous kinetics models have treated the amorphous phase as uniform on an atomic scale, but recent structural analysis has revealed atomic scale spatial heterogeneities. A new kinetics analysis will be developed to treat the spatially heterogeneous state and tested with nanocrystal nucleation measurements in amorphous Al-Y-Fe alloys. The results have a broader relevance to the nature of primary crystallization as a common devitrification reaction in many metallic glasses. An important component of the project effort will be the education of graduate students and the research experience for undergraduate and high school students. Further, lecture demonstrations on nanostructured materials will be incorporated into campus outreach programs for high school and incoming undergraduate students.