Effects of Nanoscale Grain Boundary Composition Fluctuations on Mechanical Behavior of Metals and Alloys

技术：金属和合金局部成分的变化是材料科学和工程(MS&Amp；E)许多基本方面的关键。这些变化在组成上的差异可能很大，但它们通常在空间范围上很小，通常发生在一纳米或更小的范围内。当成分波动与多晶材料中的缺陷相关时，它们可能会引起有害的性质变化，例如，通过氢、回火或辐射增强的脆化，金属和合金的灾难性脆性破坏。直到最近，还不可能直接测量这些成分的变化，并将它们与材料的机械行为、结晶学、电子结构和缺陷结构联系起来。然而，这样的测量现在是可能的。在之前的一次NSF拨款中，PI开发了对少量材料进行机械测试的方法，包括可能包含单一晶界的样品。在之前的两次NSF赠款中，共同PI参与了两台经像差校正的透射电子显微镜(TEM)的购置，并开发了计算机处理方法，以检测和量化大量晶界(GB)和沉淀物的亚纳米级成分变化。已在模型系统和商业合金中获得了初步数据。本项目的目标是探索和准确量化金属和合金中与GB偏析相关的纳米级成分变化，并通过直接测试和建模建立GB特征与力学行为之间的联系。汇集在一起的国际合作者团队拥有多种技能，通过将最先进的电子显微镜/光谱分析和3D原子探针方法与最新的第一性原理模拟和现场机械测试技术独特地结合在一起，将增强对GB结晶学和当地化学之间复杂相互作用的理解。这项研究将产生迄今为止无法获得的与晶界偏析相关的成分和力学行为数据，从数百甚至数千个现在可以首次分析的特定界面中挑选出来。非技术性：这项研究的更广泛影响将通过修订成分变化对偏析和机械性能的作用的基本理解而产生，这是所有MS&A；E学生的教育和培训的核心。这些材料表征方面的最新进展将加强研究和教育基础设施，并将在利哈伊？S年度显微镜学校教授利哈伊？S年度显微镜学校的许多班级学生和数以百计的工业参与者，该学校现已进入第38个年头。结果将通过技术介绍、出版物和新教科书向材料界传播。在测量金属和合金中纳米级元素变化方面的改进有可能修改偏析的基本理论，并将为未来类似的沉淀研究奠定基础。反过来，这些知识可能会允许重新设计控制材料特性的标准制造和加工方法。因此，通过改善物质基础设施、氢经济、航空航天和汽车的金属和合金，长期结果可能会在最广泛的意义上影响社会。

TECHNICAL: Changes in the local composition of metals and alloys are key to many fundamental aspects of materials science and engineering (MS&E). These variations may be large in compositional difference, but they are usually small in spatial extent, often occurring over a nanometer or less. When composition fluctuations are associated with defects in polycrystalline materials, they may induce deleterious property changes, such as the catastrophic brittle failure of metals and alloys via, for example, hydrogen-, temper-, or irradiation-enhanced embrittlement. Until recently, it has not been possible to measure these composition changes directly and relate them to the mechanical behavior, the crystallography, the electronic structure, and the defect structure of the material. However, such measurements are now possible. In a previous NSF grant, the PI has developed methods for mechanical testing of small volumes of material, including samples that can contain a single grain boundary. In two prior NSF grants, the co-PI has participated in the acquisition of two aberration-corrected transmission electron microscopes (TEMs) and has developed computer-processing methods to detect and quantify sub-nanometer scale composition changes at large numbers of grain boundaries (GBs) and precipitates. Initial data have been obtained in model systems and commercial alloys. The objective of this project is to explore and accurately quantify nanoscale composition changes associated with GB segregation in metals and alloys, and to establish the connections between GB character and mechanical behavior through direct testing and through modeling. The assembled team of international collaborators has combined skills that will enhance understanding of the complex interplay between GB crystallography and local chemistry via a unique combination of the most advanced electron microscopy/spectroscopy and 3D atom-probe methods with the latest first-principles simulations and in-situ mechanical testing techniques. The research will generate hitherto-unobtainable composition and mechanical behavior data associated with grain-boundary segregation, selecting specific interfaces from hundreds or even thousands that can now be analyzed for the first time. NON-TECHNICAL: The broader impact of this research will arise through the potential to revise the basic understanding of the role of composition variations on segregation and mechanical properties, which are central to the education and training of all MS&E students. These latest advances in materials characterization will enhance the research and education infrastructure and will be taught to many classes of Lehigh students and hundreds of industrial attendees at Lehigh?s Annual Microscopy School, now in its 38th year. The results will be disseminated to the materials community through technical presentations, publications and a new textbook. Improvements in the measurement of nanoscale elemental changes in metals and alloys have the potential to modify basic theories of segregation, and will lay the groundwork for similar studies of precipitation in the future. In turn, this knowledge may permit the re-design of standard fabrication and processing methods that control the properties of materials. Thus the long-term result may affect society in the broadest sense through improved metals and alloys for the physical infrastructure, the hydrogen economy, aerospace and automobiles.