MRI: Acquisition of a Plasma Focused Ion Beam System for Dynamic In-situ Micro-Mechanical Testing Over Cryogenic and Elevated Temperatures

在微/纳米尺度上直接观察变形行为可以通过将微观结构变化与载荷-位移特性联系起来，从而使我们对材料变形机制的理解取得重大进展。例如，裂纹尖端的扩展会导致部件的灾难性失效，或者变形/温度引起的相变和结晶度变化是导致材料失效的重要加工现象。该项目中的等离子体聚焦离子束（FIB）使研究人员能够有效地从材料中感兴趣的特定部位提取样品进行微力学测试，这可以使用集成在同一FIB仪器中的最先进的微力学测试设备进行。使用该系统可以观察到变形过程中发生的微观结构和晶体学变化，这些变化可以与局部应力-应变数据直接相关。该设备将有利于利哈伊大学材料科学领域的各种资助研究活动，包括陶瓷、金属/合金、3d打印材料、聚合物和生物材料。此外，在等离子体FIB中实现的快速材料去除率加速了各种纳米结构的制造，例如微/纳米注塑模具，以及在低温下对各种样品（包括高敏感生物材料和软聚合物）进行大规模内部表征。该仪器还通过利哈伊已经建立的联络项目支持其他大学、政府实验室和工业界的研究项目。使用该系统开发的技术和知识与利哈伊学生以及利哈伊显微镜学校的众多行业/政府参与者共享。该系统由(1)等离子体聚焦离子束（FIB）仪器组成，集成了(2)具有宽温度范围测试能力的最先进的原位微机械测试设备和(3)高速电子背散射衍射（EBSD）相机。该系统将能够在机械测试期间同时获取多种类型的数据，包括高灵敏度传输菊池衍射模式。基于氙离子的等离子体FIB的快速铣削速率是传统镓离子系统的10-100倍，显着提高了微机械测试样品的制造吞吐量，从而解决了目前严重的限制，即测试具有统计学意义的样品数量的能力。在零下130到1000摄氏度的温度下，FIB内的原位力学测试将使变形过程（如滑移和微裂纹/空洞成核）与纳米尺度的微观结构特征相关联。此外，负载位移信号可以在1.2 MHz的频率下采样，这比扫描电镜成像中遇到的典型帧速率快得多。该信息将由数字图像相关补充，这将用于量化局部变形。这些功能是非常有利的，但使所要求的仪器真正独特的是在机械测试期间同时提取实时EBSD数据的能力，这是由一种新颖的测试平台几何结构实现的。此外，用于表征多组分材料以及材料和器件中的界面和边界等特定特征的串行截面的效率得到了极大的提高。低温下的样品切片能力对于软材料（如聚合物和生物样品）的横截面观察以及薄样品制备（允许在透射电子显微镜下进行更详细的观察）特别有用。该奖项反映了美国国家科学基金会的法定使命，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。

Direct observation of deformation behavior at the micro/nano scales can lead to significant advances in our understanding of the deformation mechanisms in materials by correlating microstructural changes with load-displacement characteristics. For example, the propagation of a crack-tip that would lead to a catastrophic failure of a component, or deformation/temperature-induced phase transformations and crystallinity changes are important processing phenomena that can lead to failure in materials. The plasma focused ion beam (FIB) in this project allows researchers to efficiently extract samples from specific sites of interest in materials for micromechanical testing, which can be performed using a state-of-the-art micromechanical testing device integrated within the same FIB instrument. It is possible to observe both microstructural and crystallographic changes that occur during deformation using this system, and these changes can be directly correlated with localized stress-strain data. The equipment will benefit a wide variety of funded research activities at Lehigh across sectors of materials science ranging from ceramics, metals/alloys, 3D-printed materials, polymers and biomaterials. In addition, the rapid material removal rate achievable in the plasma FIB accelerates the fabrication of a wide range of nanostructures such as tooling for micro/nano injection molding, as well as enable large-scale internal characterization of various samples including highly sensitive biomaterials and soft polymers at cryogenic temperatures. The instrument also supports research projects from other universities, government labs and industry through liaison programs already established at Lehigh. The techniques and knowledge developed using this system are shared with Lehigh students as well as numerous industry/government attendees of the Lehigh Microscopy Schools. The system as specified consists of (1) a plasma focused ion beam (FIB) instrument, integrated with (2) a state-of-the-art in-situ micromechanical testing device with testing capability over a wide temperature range and (3) a high speed electron backscattered diffraction (EBSD) camera. The system will be able to simultaneously acquire many types of data, including highly sensitive transmission Kikuchi diffraction patterns, during mechanical testing. The rapid milling rate of the Xe-ion based plasma FIB, which is ~10–100 times greater than conventional Ga-ion systems, markedly increases the fabrication throughput of micromechanical test samples, and hence addresses what is currently a severe limitation, namely the ability to test a statistically significant number of samples. In-situ mechanical testing within the FIB at temperatures from minus 130 to 1000 degrees C will enable the correlation of deformation processes (such as slip and microcrack/void nucleation) with microstructural features at the nm scale. Furthermore, the load-displacement signals can be sampled at 1.2 MHz, which is much faster than the typical frame rates encountered in SEM imaging. This information will be complemented by digital image correlation, which will be used to quantify localized deformation. These capabilities are highly advantageous, but what makes the requested instrumentation truly unique is the ability to simultaneously extract real time EBSD data during mechanical testing, which is made possible by a novel test platform geometry. Moreover, the efficiency of serial cross-sectioning for the characterization of multi-component materials, as well as specific features such as interfaces and boundaries in materials and devices, is improved tremendously. The sample sectioning capability at cryogenic temperatures is especially useful for cross-sectional observation of soft materials such as polymers and biological samples, and for thin-specimen preparation to allow more detailed observation in a transmission electron microscope.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.