Atomic Scale Studies of Heterophase Metallic Interfaces

小行星9728986 本研究的主要推力是在同一合金系统中开发的特性良好的相干和半相干异相界面的偏析检查。 样品制备主要通过固态分解反应或内部氮化来实现，以产生具有原子级清洁界面的沉淀物。 随后进行低温处理以诱导三元或四元元素的偏析。 低于一个临界直径的沉淀物是连贯的，而在此直径以上，他们是半相干的，允许在任何相干或半相干界面的偏析的研究。 最高分辨率的技术，包括原子探针场离子和三维原子探针显微镜，高分辨率和扫描透射电子显微镜，和空间分辨电子能量损失光谱，采用。 在所研究的系统中，既包括有技术意义的界面，也包括“模型”界面，它们是Al/Al 3Sc（Mg）（一种航空航天结构合金）; Al（Cu）和Cu（Sn或In）（集成电路互连）; Fe/Mo、Fe/Mo（V）; α-Fe/氮化钼（Sn）; Au/Ni，有和没有偏析物。 异相界面的理论建模解决了界面结构和界面处偏析物的性质。 建模采用从头计算密度泛函理论计算，分子动力学和蒙特卡罗模拟，和连续弹性理论。 %偏析原子在技术上重要的异相金属界面的物理和机械性能中起着至关重要的作用。 隔离剂对于定制界面性质是重要的，例如，通过以受控的量引入选定的微合金化溶质。 从共格到半共格沉淀物的临界过渡直径的控制在技术上是重要的，因为它决定了材料微观结构的稳定性。 ***

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. ***