Atomic Structure and Properties of Transformation Interfaces in Metal Alloys

技术支持：本研究的目的是在原子水平上了解金属合金相变界面的原子结构和性质。在属性方面，研究特别感兴趣的是原子附着到界面的机制及其动态行为，以及诸如偏析和/或溶质分配对转化过程的作用等因素。该研究计划集中在两种类型的转换界面，这些界面在很大程度上未经实验探索，因此，为发现新的基础科学现象提供了相当大的机会。这些是：1）固-液界面，其将使用过共沸Al-Si-Cu-Mg合金纳米颗粒来研究，以及2）化学扩散界面，其将使用有序Au-Cu（-Ag）合金纳米颗粒来研究。对于固-液界面，研究计划确定在界面处发生的成分和结构变化是否完全相关，是否可以观察和量化预测在固-液界面处发生的空间或时间波动，以与原子模拟和此类现象的理论预测进行比较，以及某些合金物种是否分离到界面，用于与基于合金热力学的预测进行比较。类似的方面将研究有序合金中的扩散界面，特别是，确定扩散界面的宽度是否随转变的驱动力而增加，是否在三元合金中发生这种界面的偏析，以及界面波动的空间范围和时间行为是否取决于温度。使用原位TEM进行这些研究的特别优点是能够直接观察和量化界面行为及其对精确控制的过冷度的响应，例如，开氏度的分数，具有亚纳米的化学和空间分辨率。非技术性：固液界面在科学和技术上都是非常重要的，但在金属合金中的实验数据很少。本研究将使用先进的原位TEM技术和分析来研究重要界面的结构、化学和动力学行为。它将推动界面科学、相变和原位TEM领域的发展。研究生和本科生都将参与研究，并使用先进的实验TEM技术和分析。学生将获得材料科学和显微镜专业知识，他们将需要成为毕业后在该领域的生产力研究人员。将为代表性不足的学生提供充分的机会参加这项研究，特别是在本科阶段。

TECHNICAL: The purpose of this research is to understand the atomic structure and properties of transformation interfaces in metal alloys at the atomic level. In terms of properties, the research is particularly interested in the mechanisms of atomic attachment to interfaces and their dynamic behavior, as well as factors such as the role of segregation and/or solute partitioning on the transformation process. The research plans to concentrate on two types of transformation interfaces that are largely unexplored experimentally and therefore, offer considerable opportunity to discover new fundamental scientific phenomena. These are: 1) the solid-liquid interface, which will be investigated using hypereutectic Al-Si-Cu-Mg alloy nano-particles, and 2) chemically diffuse interfaces, which will be investigated using ordered Au-Cu(-Ag) alloy nano-particles. For the solid-liquid interface, the research plans to determine whether the compositional and structural changes that occur at the interface are exactly correlated, whether it is possible to observe and quantify spatial or temporal fluctuations that are predicted to occur at solid-liquid interfaces for comparison with atomistic simulations and theoretical predictions of such phenomena, and whether certain alloy species segregate to the interface, for comparison with predictions based on the alloy thermodynamics. Similar aspects will be investigated for diffuse interfaces in ordered alloys, in particular, determining whether the width of a diffuse interface increases with driving force for transformation, whether segregation occurs to such interfaces in ternary alloys, and whether the spatial extent and temporal behavior of interface fluctuations depend on temperature. Particular advantages of performing these studies using in-situ TEM are the ability to directly observe and quantify the interface behavior and its response to precisely controlled under-cooling, e.g., fractions of a degree Kelvin, with sub-nanometer chemical and spatial resolution. NON-TECHNICAL: The solid-liquid interface is very important both scientifically and technologically, but there are few experimental data available in metal alloys. This research will investigate the structural, chemical and dynamic behavior of important interfaces using sophisticated in-situ TEM techniques and analysis. It will advance the fields of interface science, phase transformations and in-situ TEM. Both the graduate and undergraduate students will be involved in research, and use sophisticated experimental TEM techniques and analyses. The students will acquire the materials science and microscopy expertise that they will need to become productive researchers in the field after graduation. Ample opportunities will be provided for underrepresented students to participate in this research, particularly at the undergraduate level.