9728986 Seidman The principal thrust of this study is examination of segregation at well-characterized coherent and semicoherent heterophase interfaces developed in the same alloy system. Specimen preparation is achieved primarily via solid-state decomposition reactions or internal nitridation to produce precipitates with atomically clean interfaces. This is followed by low-temperature treatments to induce segregation of ternary or quaternary elements. Below a critical diameter the precipitates are coherent, while above this diameter they are semicoherent, allowing a study of segregation at either coherent or semicoherent interfaces. The highest resolution techniques available, including atom- probe field-ion and three-dimensional atom-probe microscopies, high-resolution and scanning transmission electron microscopies, and spatially resolved electron- energy-loss spectroscopy, are employed. Among the systems investigated, which include both interfaces of technological interest and `model' interfaces, are Al/Al3Sc (Mg) (an aerospace structural alloy); Al(Cu) and Cu(Sn or In) (interconnects for integrated circuits); Fe/Mo, Fe/Mo(V); alpha-Fe/molybdenum nitride (Sn); Au/Ni, with and without segregants. Theoretical modeling of heterophase interfaces addresses the interface structure and the properties of the segregants at the interfaces. The modeling employs ab initio density functional theory calculations, molecular dynamics and Monte Carlo simulations, and continuum elasticity theory. %%% Segregating atoms play a crucial role in the physical and mechanical properties of technologically significant heterophase metallic interfaces. Segregants are important for tailoring interfacial properties, e.g., by the introduction of selected microalloying solutes in controlled quantities. Control of the critical transition diameter from coherent to semicoherent precipitates is technologically important, as it determines the stability of the microstructure of the m aterial. ***
