Atomic Structure and Properties of Transformation Interfaces in Metal Alloys

技术：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。在性质方面，该研究特别关注原子在界面上附着的机制及其动态行为，以及偏析和/或溶质分配在相变过程中的作用等因素。这项研究计划集中在两种类型的转换界面上，这两种界面在很大程度上没有被实验探索，因此，为发现新的基本科学现象提供了相当大的机会。它们是：1)固-液界面，将用过共晶Al-Si-铜-镁合金纳米颗粒研究；2)化学扩散界面，将用有序Au-Cu(-Ag)合金纳米颗粒研究。对于固-液界面，这项研究计划确定界面上发生的成分和结构变化是否完全相关，是否有可能观察和量化预测发生在固-液界面上的空间或时间波动，以便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偏析到界面，以便与基于合金热力学的预测进行比较。对于有序合金中的扩散界面也将进行类似的研究，特别是确定扩散界面的宽度是否随着相变驱动力的增加而增加，三元合金中的扩散界面是否发生偏析，以及界面波动的空间范围和时间行为是否取决于温度。使用原位电子显微镜进行这些研究的特殊优势是能够直接观察和量化界面行为及其对精确控制的过冷的响应，例如，具有亚纳米化学和空间分辨率的开尔文分数。非技术：固-液界面在科学和技术上都非常重要，但金属合金的实验数据很少。这项研究将利用先进的原位透射电子显微镜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、相变和原位透射电子显微镜等领域的发展。研究生和本科生都将参与研究，并使用复杂的实验瞬变电磁技术和分析。这些学生将获得材料科学和显微镜专业知识，这些专业知识将使他们在毕业后成为该领域富有成效的研究人员。将为代表性不足的学生提供充足的机会参与这项研究，特别是在本科生水平。

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.