The purpose of this research is to understand the dynamic behavior, electron states, and interfacial energies of important transformation interfaces in metal alloys. The proposed research will concentrate on two types of interfaces that are still largely unexplored, and therefore, offer considerable opportunity to discover new fundamental scientific phenomena regarding their behavior. These are the solid-liquid interface, which will be investigated using Al-Si base alloy powder particles, and incoherent interphase boundaries, which will be investigated using massive transformation interfaces in Mn-Al(-C) alloys. Some specific questions that will be addressed in the proposed research are: i) Does equilibrium segregation occur at solid-liquid interfaces, can it be predicted from thermodynamics, and does it precede nucleation of a new phase at the interface? ii) Do faceted crystals present their slowest-growing interfaces during growth and their fastest-growing interfaces during dissolution as theory suggests? iii) How do interfacial fluctuations that are observed at interfaces between solid Si and solid Al and liquid Al-Si alloy occur, and how do they compare quantitatively with each other and with computer simulations? iv) How do atoms and electrons behave in liquid Al and Al-Si alloys as the liquids are undercooled in terms of the core and valence electron states, and is ordering in the liquid revealed in these properties? v) Do solid-liquid interface plasmons exist and if so, what are their properties? vi) Do low-index interfaces (e.g. {111}) form during the massive transformation for the same reasons as for grain boundaries? vii) Do {111} random grain boundaries and incoherent massive interfaces both migrate by the movement of atomic steps parallel to the {111} facet? These problems will be answered using a combination of in-situ analytical transmission electron microscopy (TEM) and other complementary experimental and computational techniques.
NON-TECHNICAL SUMMARY: The nature of the solid-liquid interface is extremely important both scientifically and technologically. For example, almost all engineering metal alloys, such as those found in automobiles, jet engines and construction beams, start as a liquid mixture that changes into a solid at the solid-liquid interface on cooling. Likewise, the silicon wafers that are the basis of computer technology are large single-crystals that are grown from a liquid melt. In spite of the importance of the solid-liquid interface in these processes, there are few experimental data available that directly show how the different elements in the liquid mixture partition into the solid and liquid phases at the solid-liquid interface. This research will show precisely how this occurs. Another important technological interface that forms between two crystalline solids is called an incoherent interface. This type of interface is also found in almost all useful engineering metals such as those mentioned above, in the form of random grain and interphase boundaries. Knowledge of the properties of such interfaces and how they behave during metal processing is limited, but this research will reveal these phenomena. In summary, this research will generate entirely new information about important technological solid-liquid and solid-solid interfaces, thereby enhancing our ability to control such interfaces to make better engineering materials that are used throughout society. The results of this research will be widely disseminated by making the in-situ microscope videos obtained during the work available online, so that faculty, students and researchers will be able to observe the videos and use them to further their understanding and teaching of interface science.
