Atomic Structure and Properties of Transformation Interfaces in Metal Alloys

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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.