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

了解和控制赋予钨和 BCC 金属室温延展性的原子尺度机制

基本信息

批准号：
1727740
负责人：
Vijay Gupta
金额：
$ 46.32万
依托单位：
University of California-Los Angeles
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-15 至 2021-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1727740&HistoricalAwards=false
关键词：
Understanding Controlling Atomic Scale Mechanisms

项目摘要

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.

钨(W)重量轻，熔点是金属中最高的。在极端温度下也能保持超高的强度和硬度。这使得它可以用于对美国经济很重要的几种高温应用，例如白炽灯泡的灯丝（家用），熔炉的加热元件（制造），磁聚变能装置（替代能源），发动机和面向等离子体的部件（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。钨和其他BCC金属的一个主要问题是，它们在室温下非常脆，因此很难用模具和其他成型工艺加工或成型，这使得它们价格昂贵，并限制了它们更广泛的应用。相比之下，面心立方（FCC）金属（如铜）柔软且易于加工，但它们不具有许多应用所需的高强度和硬度。该奖项通过理解和控制极小晶粒尺寸的原子群的运动，探索可能赋予室温延展性的机制，就像FCC金属所显示的那样，钨和其他BCC金属，这些原子群一起形成了这些金属的结构。这项研究涉及多个学科，包括物理、机械工程、制造和材料科学。接受此项目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参加为期一年和夏季的活动，为他们应对快速发展的技术工作空间中的挑战做好准备。本研究将考察i)尺寸和温度对流动应力的影响，ii)应变速率和低温对流动应力的影响，以及iii)温度、应变速率和尺寸对BCC金属断裂韧性的影响。本研究将包括基于聚焦离子束（FIB）的纳米柱和缺口纳米级三点弯曲试样的制造，基于低应变率的微压头变形和基于高应变率的激光碎裂变形，在一定温度范围内（100K,900K）的拉伸、压缩和弯曲载荷下，以及基于特定位置的基于FIB的电子透明TEM样品制备，用于位错表征。结果将直接与离散位错和裂纹动力学模拟的预测结果进行比较。该研究可能会导致发现新的位错成核和迁移机制，并进一步了解BCC金属目前的性能极限。