Properties and Behavior of Transformation Interfaces in Metal Alloys

金属合金中相变界面的性质和行为

• 批准号: 1106230
• 负责人: James Howe
• 金额: $ 57.7万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1106230&HistoricalAwards=false
• 关键词: Properties; Behavior; Transformation; Interfaces; Metal

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.

技术概要：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，这些界面在很大程度上尚未被探索，因此，提供了相当大的机会来发现有关其行为的新的基础科学现象。这些是固-液界面，这将使用Al-Si基合金粉末颗粒进行研究，以及非相干相间边界，这将使用Mn-Al（-C）合金中的块状转变界面进行研究。在所提出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处，它是否可以从热力学预测，以及它是否先于界面处新相的成核？ii）多面晶体在生长过程中呈现出最慢生长的界面，而在溶解过程中呈现出最快生长的界面，这与理论所表明的一致吗？iii）在固体Si与固体Al和液体Al-Si合金之间的界面处观察到的界面波动是如何发生的，它们如何定量地相互比较以及与计算机模拟进行比较？iv）当液体过冷时，原子和电子在液体Al和Al-Si合金中的行为如何，就核心和价电子态而言，这些性质是否揭示了液体中的有序性？5）固液界面等离子体存在吗？如果存在，它们的性质是什么？vi）低折射率界面（例如{111}）在大规模转变期间是否由于与晶界相同的原因而形成？vii）{111}随机晶界和非相干块状界面都通过平行于{111}面的原子台阶的移动而迁移吗？这些问题将使用原位分析透射电子显微镜（TEM）和其他互补的实验和计算技术的组合来回答。非技术性总结：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，喷气发动机和建筑梁中发现的那些，开始时是液体混合物，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态熔体中生长出来的大单晶体。尽管在这些过程中的固-液界面的重要性，有很少的实验数据，直接显示在液体混合物中的不同元素如何分配到固相和液相在固-液界面。这项研究将准确地显示这是如何发生的。在两种结晶固体之间形成的另一个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，以随机晶粒和相间边界的形式。这些界面的性质以及它们在金属加工过程中的行为的知识是有限的，但这项研究将揭示这些现象。总之，这项研究将产生有关重要技术固-液和固-固界面的全新信息，从而提高我们控制这些界面的能力，以制造更好的工程材料，供全社会使用。这项研究的结果将通过在线提供工作期间获得的原位显微镜视频来广泛传播，以便教师，学生和研究人员能够观察视频并使用它们来进一步理解和教学界面科学。