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Exploring Dislocation Structures with Conventional EBSD

使用传统 EBSD 探索位错结构

基本信息

批准号：
2125895
负责人：
Ulrich Faul
金额：
$ 22.37万
依托单位：
SUNY College at New Paltz
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-09-01 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2125895&HistoricalAwards=false
关键词：
Exploring Dislocation Structures Conventional EBSD

项目摘要

The interior of the Earth is not frozen but continuously turns over. The motion of rigid plates at the Earth’s surface is driven by the thermal convection of solid rocks in the planet interior. Plate tectonics likely began early in Earth’s history. The continuous deformation leaves a record within rocks that can be sampled at the surface. Such a record is also observed in minerals and rocks deformed experimentally at conditions reproducing natural deformations. The record includes the size and shape of the minerals forming the rocks, called microstructure, as well as specific defects within individual crystals. These defects contain critical information about the permanent deformation – called plastic deformation – that the mineral experienced. A key ingredient of crystal plastic deformation, first recognized and extensively studied in metals, are line defects called dislocations. These small linear defects can be imaged by electron microscopy. Yet, because of their small size, it is challenging to observe them together with their host crystal, usually much larger. Here, the team develops a new method to image dislocations over areas that are representative of the microstructure of natural rocks. The method, based on scanning electron microscopy, can be routinely applied to experimentally and naturally deformed rocks. It provides a new time- and cost-effective way to study processes that shape the Earth. The researchers first benchmark the method on crystals which have been experimentally deformed and extensively studied by a range of imaging techniques. They then apply the new imaging technique to naturally deformed rocks, gradually unveiling their deformation history. The project supports an early-career female scientist and the training of undergraduate students at SUNY College at New Paltz (NY). Its outcomes provide the scientific community with a blueprint for improving microstructural studies of Earth materials.Most of the Earth's crust and upper mantle deform by dislocation creep. Grain-internal structures of experimentally and naturally deformed samples are usually examined either by oxidative decoration of dislocations or TEM imaging. The former is not a routine analysis method and cannot resolve the full geometry of dislocations. While the latter comprehensively characterizes dislocations, the investigated volume is only a few microns, a fraction of the grain size even of fine-grained experimental samples. Up to now, electron backscatter diffraction (EBSD) mapping has primarily been used to determine grain sizes and lattice preferred orientation; but the speed and quality of EBSD indexing has substantially improved over the last decade. Automated EBSD mapping allows routine imaging of relatively large areas (up to thin section scale). High-resolution EBSD mapping has been shown to be able to image dislocation structures in olivine and quartz. HR-EBSD, however, requires substantial additional resources in comparison to conventional EBSD. Here, the team investigate whether conventional EBSD mapping can provide accurate enough indexing to characterize dislocation type/slip systems, for both distributed dislocations and sub-grain boundaries. To test the method, the team map single crystals previously deformed experimentally, for which the dislocation structures have been comprehensively evaluated by oxidative decoration and TEM. The method will then applied to natural samples with different fabric types, which allows indexing their dislocation microstructures in a cost-effective way.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球内部并不是冻结的，而是不断地翻转。地球表面刚性板块的运动是由行星内部固体岩石的热对流驱动的。板块构造可能在地球历史的早期就开始了。这种连续的变形在岩石中留下了记录，可以在地表取样。在矿物和岩石中也观察到这样的记录，这些矿物和岩石在再现自然变形的条件下进行了实验变形。记录包括形成岩石的矿物的大小和形状，称为微观结构，以及单个晶体内的特定缺陷。这些缺陷包含有关矿物经历的永久变形（称为塑性变形）的关键信息。晶体塑性变形的一个关键成分，首先在金属中被认识和广泛研究，是称为位错的线缺陷。这些小的线性缺陷可以通过电子显微镜成像。然而，由于它们的尺寸很小，将它们与通常大得多的宿主晶体一起观察是具有挑战性的。在这里，该团队开发了一种新的方法来对代表天然岩石微观结构的区域的位错进行成像。该方法，基于扫描电子显微镜，可以常规地应用于实验和自然变形的岩石。它提供了一种新的时间和成本效益的方式来研究塑造地球的过程。研究人员首先将该方法用于晶体，这些晶体已经过实验变形，并通过一系列成像技术进行了广泛研究。然后，他们将新的成像技术应用于自然变形的岩石，逐渐揭示其变形历史。该项目支持一名职业生涯初期的女科学家和纽约州立大学新帕尔茨学院（纽约州）本科生的培训。它的成果为科学界提供了一个改善地球材料微观结构研究的蓝图。实验和自然变形样品的晶粒内部结构通常通过位错的氧化装饰或TEM成像来检查。前者不是一种常规的分析方法，不能解析位错的全部几何形状。虽然后者全面表征位错，但所研究的体积仅为几微米，甚至是细晶粒实验样品的晶粒尺寸的一小部分。到目前为止，电子背散射衍射（EBSD）绘图主要用于确定晶粒尺寸和晶格择优取向;但EBSD索引的速度和质量在过去十年中有了很大的提高。自动化EBSD映射允许相对较大区域的常规成像（直到薄切片规模）。高分辨率EBSD成像已被证明能够成像橄榄石和石英中的位错结构。然而，与传统的EBSD相比，HR-EBSD需要大量额外的资源。在这里，研究小组调查了传统的EBSD映射是否可以提供足够准确的索引来表征分布式位错和亚晶界的位错类型/滑移系统。为了测试这种方法，该团队绘制了先前实验变形的单晶，通过氧化装饰和TEM对位错结构进行了全面评估。该方法将应用于具有不同结构类型的天然样品，从而以具有成本效益的方式索引其位错微观结构。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。