Voisin Thomas, Grapes Michael D, Zhang Yong, Lorenzo Nicholas, Ligda Jonathan, Schuster Brian, Weihs Timothy P
Dept. of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Dept. of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
Ultramicroscopy. 2017 Apr;175:1-8. doi: 10.1016/j.ultramic.2016.12.001. Epub 2016 Dec 5.
To model mechanical properties of metals at high strain rates, it is important to visualize and understand their deformation at the nanoscale. Unlike post mortem Transmission Electron Microscopy (TEM), which allows one to analyze defects within samples before or after deformation, in situ TEM is a powerful tool that enables imaging and recording of deformation and the associated defect motion during mechanical loading. Unfortunately, all current in situ TEM mechanical testing techniques are limited to quasi-static strain rates. In this context, we are developing a new test technique that utilizes a rapid straining stage and the Dynamic TEM (DTEM) at the Lawrence Livermore National Laboratory (LLNL). The new straining stage can load samples in tension at strain rates as high as 4×10/s using two piezoelectric actuators operating in bending while the DTEM at LLNL can image in movie mode with a time resolution as short as 70ns. Given the piezoelectric actuators are limited in force, speed, and displacement, we have developed a method for fabricating TEM samples with small cross-sectional areas to increase the applied stresses and short gage lengths to raise the applied strain rates and to limit the areas of deformation. In this paper, we present our effort to fabricate such samples from bulk materials. The new sample preparation procedure combines femtosecond laser machining and ion milling to obtain 300µm wide samples with control of both the size and location of the electron transparent area, as well as the gage cross-section and length.
为了模拟金属在高应变速率下的力学性能，可视化并理解其在纳米尺度下的变形非常重要。与能够在变形前后分析样品内部缺陷的事后透射电子显微镜（TEM）不同，原位TEM是一种强大的工具，能够在机械加载过程中对变形及相关缺陷运动进行成像和记录。不幸的是，目前所有的原位TEM力学测试技术都仅限于准静态应变速率。在此背景下，我们正在劳伦斯利弗莫尔国家实验室（LLNL）开发一种利用快速应变台和动态TEM（DTEM）的新测试技术。新的应变台可以使用两个在弯曲状态下工作的压电致动器，以高达4×10/s的应变速率对样品进行拉伸加载，而LLNL的DTEM可以在电影模式下以低至70ns的时间分辨率进行成像。鉴于压电致动器在力、速度和位移方面存在限制，我们开发了一种制造具有小横截面积的TEM样品的方法，以增加施加的应力，并采用短标距长度来提高施加的应变速率，同时限制变形区域。在本文中，我们展示了从块状材料制备此类样品的工作成果。新的样品制备程序结合了飞秒激光加工和离子铣削技术，以获得宽度为300µm的样品，同时控制电子透明区域的尺寸和位置以及标距横截面和长度。
