Understanding and Controlling Atomic-Scale Mechanisms for Imparting Room Temperature Ductility in Tungsten and BCC Metals

钨（W）重量轻，熔点最高的金属。它在极端温度下保持其抗弯强度和硬度。这使得它可以用于对美国经济非常重要的几种高温应用中，例如白炽灯泡（家用）的灯丝，熔炉（制造）的加热元件，磁聚变能源设备（替代能源），发动机和面向等离子体的组件（运输）以及空间电力推进（科学进步）。 钨属于所谓的体心立方（BCC）类多晶金属。W和其他BCC金属的主要问题之一是它们在室温下非常脆，因此很难使用模具和其他成形工艺加工或成形为形状，这使得它们昂贵并限制了它们更广泛的使用。 相比之下，面心立方（FCC）金属如铜是软的且易于加工，但它们不具有许多应用所需的高强度和硬度。该奖项探索了可能赋予钨和其他BCC金属室温延展性的机制，如FCC金属所显示的，通过理解和控制极小晶粒尺寸的原子团的运动，这些原子团共同形成这些金属的结构。这项研究涉及多个学科，包括物理学，机械工程，制造和材料科学。在这个项目上培训的研究生将跨越学科界限，学习广泛的知识和技能。本科生和高中生将分别通过为期一年和夏季的参与来适应，为他们在快速发展的技术工作空间中应对挑战做好准备。该研究将检查i）尺寸和温度对流动应力的影响，ii）应变速率和低温温度对流动应力的影响，以及iii）温度、应变速率和尺寸对BCC金属断裂韧性的影响。这项研究将涉及基于聚焦离子束（FIB）的纳米柱和缺口纳米级三点弯曲试样的制造，在低应变率下基于picoindentor的变形和在高应变率下基于激光溅射的变形在拉伸，压缩和弯曲载荷在一个温度范围内（100 K，900 K），和特定的FIB基于电子透明TEM试样制备位错表征。结果将直接与离散位错和裂纹动力学模拟的预测进行比较。这项研究可能会导致新的位错成核和迁移机制的发现，并提供进一步的了解BCC金属目前的性能限制。

Tungsten (W) is lightweight, with the highest melting point among metals. It retains its ultrahigh strength and hardness at extreme temperatures. This allows it to be used in several high temperature applications that are important to the U.S. economy, such as, filaments for incandescent bulbs (household), heating elements for furnaces (manufacturing), magnetic fusion energy devices (alternative energy), engine and plasma-facing components (transportation), and space electric propulsion (advancement of science). Tungsten belongs to the so-called body centric cubic (BCC) class of polycrystalline metals. One of the major problems with W and other BCC metals that makes them expensive and limits their even wider use is that they are very brittle at room temperature and, therefore, are very hard to machine or form into shapes using dies and other forming processes. In contrast, face centered cubic (FCC) metals such as copper are soft and easy to machine but they do not have the high strength and hardness needed for many applications. This award explores mechanisms that may impart room temperature ductility, like that displayed by FCC metals, to tungsten and other BCC metals by understanding and controlling the movement of groups of atoms in extremely small grain sizes, which together, form the structure of these metals. This research involves several disciplines including physics, mechanical engineering, manufacturing, and materials science. Graduate students trained on this project will cross over disciplinary boundaries to learn a wide array of knowledge and skills. Undergraduate and high school students will be accommodated through year-long and summer engagements, respectively, preparing them for the challenges in the rapidly evolving technological workspace. The study will examine i) the effect of size and temperature on the flow stress, ii) the effect of strain rate and cryogenic temperatures on the flow stress, and iii) the effect of temperature, strain rate, and size on fracture toughness in BCC metals. This study will involve Focused Ion Beam (FIB)-based fabrication of nanopillars and notched nanoscale three-point bending specimens, picoindentor based deformation at low strain rates and laser spallation based deformation at high strain rates under tension, compression and bending loads over a range of temperatures (100K,900K), and site specific FIB based electron transparent TEM specimen preparation for dislocation characterization. The results will be directly compared to the predictions of Discrete Dislocation and Crack Dynamics simulations. The study will likely result in the discovery of new dislocation nucleation and mobility mechanisms, and provide further insights into the present performance limits of BCC metals.