EAPSI: Investigating Grain Boundary Strength of a Helium Implanted Engineering Alloy using Micron-Scale Tensile Testing

据美国国家公共电台报道，世界上14%的人？美国的电力是由核能提供的。目前的438座反应堆分布在30个国家，此外还有15个国家正在建设的67座新核电站，它们的规格、设计特点和结构材料都非常广泛。这些结构材料除了在高温高压和腐蚀性降解环境中工作外，还必须承受越来越多的中子辐射损伤。随着反应堆寿命的延长，它们的安全性和可靠性仍然是最重要的。然而，安全处理和测试它们变得困难和昂贵，因为它们具有高放射性。已知这种辐射会导致不必要的脆化和突然的过早失效。本项目通过将中能量氦离子束聚焦在反应堆运行温度下的样品上，模拟氦生产的高剂量辐射效应。与反应堆中的中子辐照不同，这种技术不会使样品具有放射性，但由于氦的浅层穿透深度被限制在微米深度，测试样品必须在这个长度尺度上制造。将进行微拉伸试验，以研究氦对许多核反应堆中常用的结构材料的晶界强度的影响。这项研究将与位于澳大利亚卢卡斯海茨的澳大利亚核科学技术组织（ANSTO）的Dhriti Bhattacharyya博士合作进行。Dhriti Bhattacharyya博士是一名辐射损伤专家，他开发了一种新的原位微尺度拉伸测试技术来研究核结构材料。利用聚焦离子束（FIB）铣削技术，将氦注入工程合金制成微尺度拉伸试样。这些样品将在扫描电子显微镜（SEM）内进行测试，这种方式将有效地撕开材料。S晶界，以测试氦如何影响其晶界强度，这是一种强度决定特征，对材料在延长使用期间保持完整和可靠性至关重要。除了提供定量的机械应力外，该技术还可以实时观察局部变形，为反应堆部件的最终破坏机制提供有价值的信息。选择特定类型的晶界进行研究，利用电子背散射衍射（EBSD）可以得到不同的微观结构特征，并利用透射电子显微镜（TEM）和EBSD进行测试后研究，进一步了解氦的变形机制和分布，是否沿材料偏析？S晶界。微拉伸测试方法的发展将在整个材料研究中有广泛的应用，它也将使全世界更多的实验室能够安全地进行研究，并以最小的放射性样品材料获得更好的统计数据。该奖项由美国国家科学基金会和澳大利亚科学院共同资助，隶属于东亚和太平洋暑期研究所项目，支持美国研究生进行暑期研究。

According to a NPR report, 14 percent of the world?s electricity is supplied by nuclear power. The current fleet of 438 reactors spread across 30 nations in addition to the 67 new plants under construction in 15 countries contain a large breadth of specifications, design features, and structural materials. These structural materials must withstand ever increasing amounts of neutron radiation damage in addition to operating in a high temperature and pressure and corrosive degradation environment. Their safety and reliability remain of first importance as reactor lifetimes aspire to be extended. However, they become difficult and expensive to safely handle and test because they become highly radioactive. This radiation has been known to cause unwanted embrittlement and abrupt premature failure. This project focuses on simulating the high dose radiation effect of helium production by focusing a medium energy helium ion beam on a sample at reactor operation temperature. Unlike neutron irradiation in reactors, this technique does not cause the sample to become radioactive, but because the shallow penetration depth of the helium is limited to microns in depth, test samples must be manufactured on this length scale. Micro tensile tests will be performed to investigate the effect of the helium on the grain boundary strength of a structural material commonly used in many nuclear reactors. This research will be conducted in collaboration with Dr. Dhriti Bhattacharyya at the Australian Nuclear Science and Technology Organisation (ANSTO) in Lucas Heights, Australia who is a radiation damage specialist who has developed a novel in-situ micro-scale tensile testing technique to investigate nuclear structural materials. Micro-scale tensile testing specimens will be manufactured out of helium implanted engineering alloys using focused ion beam (FIB) milling techniques. These specimens will be tested inside of a scanning electron microscope (SEM) in a fashion that will effectively pull apart the material?s grain boundaries in order to test how the helium has effected its grain boundary strength, a strength determining feature crucial to the material remaining intact and reliability during extended service. In addition to providing quantitative mechanical stresses, this technique allows for real time observation of local deformation in real time, providing valuable information concerning the ultimate failure mechanism of reactor components. Selecting of specific types of grain boundaries to investigate and different microstructural features can be made using electron backscattered diffraction (EBSD) and post-test investigations can be performed using transmission electron microscopy (TEM) and EBSD to further understand the deformation mechanisms and the distribution of the helium, concerning whether it segregates along the material?s grain boundaries. The methods development of micro-tensile testing will have a wide variety of applications in materials research as a whole, and it will also allow a greater number of labs worldwide to safely conduct research and obtain better statistics with minimal radioactive sample material.This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Australian Academy of Science.