Materials World Network/Research in Undergraduate Institutions: The True Three-Dimensional Nature of Aligned Dislocation Boundaries in Deformed Metals

该项目基于哈维·马德学院(HMC)与澳大利亚材料科学与工程学院以及澳大利亚新南威尔士大学(UNSW)的电子显微镜单元之间的合作。这也是一项本科生研究活动，因为该奖项支持HMC本科生的国际材料科学研究经验。该项目专注于解决长期存在的争议，即在轧制具有中到高层错能的变形的面心立方和体心立方金属时产生的排列的位错边界的性质。由于它们在决定屈服应力和应变硬化的各向异性方面的作用，这些位错界面的结构和起源是非常有意义的。洞察这些微观结构的真实特征对于提高基于物理的模型对宏观力学性质的预测能力是至关重要的。变形多晶中排列界面的结构和起源有两种截然相反的理论：(I)它们沿某些晶面取向，或(Ii)它们的排列主要由塑性变形过程中的宏观应力状态决定。目前支持这些理论的证据是基于二维数据，这些数据不一定揭示变形微结构的真实性质，可能导致错误的解释。为了最终解决问题和进一步的建模功能，需要边界的三维(3D)方向。使用聚焦离子束-电子背散射衍射(FIB-EBSD)层析成像技术收集三维数据。在后处理中，将FIB生成的连续切片的EBSD图组合在一起，以生成能够揭示亚微米分辨率的多种结构特征的完整晶体体积。HMC的学生领导开发新的计算工具，需要有效和准确地分析由这种方法产生的大型3D数据集。他们还改进了FIB-EBSD方法，并在同行评议的期刊和国内或国际会议上公布了他们的发现。在新南威尔士大学，受资助的本科生和首席研究员可以广泛使用电子显微镜设施和HMC无法提供的培训。因此，该项目为新南威尔士大学的物理冶金和电子显微镜专家与美国本科生之间的合作提供了一个非同寻常的机会。该奖项由材料研究部和国际科学与工程办公室共同资助。

This project is based on collaboration between Harvey Mudd College (HMC) and the School of Materials Science and Engineering and the Electron Microscope Unit at the University of New South Wales (UNSW) in Australia. It is also a Research in Undergraduate Institutions activity, as the award supports international materials science research experiences for HMC undergraduate students. The project focuses on resolving a longstanding controversy about the nature of arrays of aligned dislocation boundaries that are generated during rolling of deformed face-centered cubic and body-centered cubic metals with intermediate to high stacking fault energies. The structure and origin of these dislocation boundaries are of substantial interest due to their role in determining anisotropy in yield stress and strain hardening. Insight into the true character of these microscale structures is essential for advancing the predictive capabilities of physically-based models for macroscale mechanical properties. The two opposing theories of the structure and origin of these aligned boundaries in deformed polycrystals are: (i) they are oriented along certain crystallographic planes, or (ii) their alignment is dictated primarily by the macroscopic stress state during plastic deformation. Current evidence supporting these theories is based on two-dimensional data that does not necessarily reveal the true nature of deformation microstructures and can lead to erroneous interpretation. To definitively resolve the issue and to further modeling capabilities, three-dimensional (3D) orientations of the boundaries are required. Data in 3D is collected using focused ion beam-electron backscatter diffraction (FIB-EBSD) tomography. EBSD maps of FIB-generated serial sections are combined in post-processing to generate full crystallographic volumes capable of revealing many types of structural features at submicron resolution. HMC students lead the development of new computational tools required to efficiently and accurately analyze the large 3D data sets that result from this method. They also refine FIB-EBSD methods and present their findings in peer-reviewed journals and national or international conferences. At UNSW, the supported undergraduates and the principal investigator have extensive access to electron microscopy facilities and training unavailable at HMC. The project therefore provides an extraordinary opportunity for collaboration between UNSW's experts in physical metallurgy and electron microscopy and U.S.-based undergraduate students. This award is co-funded by the Division of Materials Research and the Office of International Science and Engineering.