Properties and Behavior of Transformation Interfaces in Metal Alloys

技术综述：本研究的目的是了解金属合金中重要相变界面的动力学行为、电子态和界面能。拟议的研究将集中在两种类型的界面上，这两种界面在很大程度上仍未被探索，因此，为发现关于它们行为的新的基本科学现象提供了相当大的机会。它们是固-液界面，将用Al-Si基合金粉末颗粒来研究；非共格界面，将用Mn-Al(-C)合金的块状转变界面来研究。在拟议的研究中将解决的一些具体问题是：i)平衡偏析是否发生在固-液界面上，是否可以从热力学上进行预测，以及它是否先于界面上的新相成核？Ii)多面晶体是否像理论所说的那样，在生长过程中出现生长最慢的界面，在溶解过程中出现生长最快的界面？Iii)在固体硅与固体铝和液态铝硅合金的界面上观察到的界面波动是如何发生的，它们之间的定量比较以及与计算机模拟的比较如何？IV)当液态Al和Al-Si合金处于过冷状态时，原子和电子在液态Al和Al-Si合金中的行为如何，这些性质是否揭示了液态中的有序性？V)固-液界面等离子激元是否存在？如果存在，它们的性质是什么？Vi)在大规模相变过程中，由于与晶界相同的原因，是否形成了低指数界面(如{111})？Vii){111}随机晶界和非共格块状界面是否都是通过平行于{111}面的原子台阶运动而迁移的？这些问题将使用原位分析、透射电子显微镜和其他补充的实验和计算技术相结合来解答。非技术概述：固-液界面的性质在科学和技术上都极其重要。例如，几乎所有的工程金属合金，如汽车、喷气发动机和建筑横梁中的合金，一开始都是液体混合物，冷却时在固液界面变成固体。同样，作为计算机技术基础的硅晶片是从液体熔化中生长出来的大单晶。尽管固液界面在这些过程中很重要，但很少有实验数据可以直接说明液体混合物中的不同元素在固液界面上是如何分配成固相和液相的。这项研究将准确地展示这种情况是如何发生的。在两种晶体固体之间形成的另一种重要的技术界面称为非相干界面。这种类型的界面也存在于几乎所有有用的工程金属中，例如上面提到的那些，以随机晶界和相界的形式存在。对这些界面的性质以及它们在金属加工过程中的表现的了解是有限的，但这项研究将揭示这些现象。总而言之，这项研究将产生关于重要的技术固-液和固-固界面的全新信息，从而增强我们控制这些界面的能力，以制造更好的工程材料，并在整个社会使用。这项研究的结果将通过在网上提供工作期间获得的原位显微镜视频来广泛传播，以便教职员工、学生和研究人员能够观察这些视频并使用它们来加深他们对界面科学的理解和教学。

TECHNICAL SUMMARY: 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.