The Structural Basis for Fracture Toughness and Elasticity of Metallic Glasses

金属玻璃断裂韧性和弹性的结构基础

• 批准号: 0705517
• 负责人: Todd Hufnagel
• 金额: $ 40万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0705517&HistoricalAwards=false
• 关键词: Structural; Basis; Fracture; Toughness; Elasticity

TECHNICAL: Bulk metallic glasses combine some of the outstanding mechanical properties of metals, including high strength and stiffness, with the processing flexibility of glasses. They do have a significant limitation, however, in that localization of plastic deformation into shear bands leads to fracture at small plastic strains, particularly in tension. Nevertheless, some metallic glasses are quite tough (with fracture energies similar to those of high strength crystalline alloys) while others are truly brittle. The origins of this difference are not well understood. An understanding of the fundamental physical mechanisms responsible would be an important contribution to the development of new alloys with improved toughness and damage tolerance. PI seeks to address this challenge through a research program that combines experimental and computational techniques to explore fundamental aspects of the competition between plastic deformation and fracture of metallic glasses. The recently observed correlation between elastic properties and fracture energy is a potentially useful link for understanding the relationship between structure and fracture. PI will examine the competition between brittle fracture and plastic flow in detail. A centerpiece of this effort will be detailed structural characterization of the plastic zone around a crack tip using high energy x-ray scattering performed in situ during loading. This technique allows measurement of elastic strain (and thus stresses) in the metallic glass with excellent (~10 um) spatial resolution in both the crystalline and amorphous phases. This will allow PI to explore the conditions under which shear bands are initiated near crack tips. As part of this effort, PI will explore the effects of three variables known to mediate the transition between brittle and tough behavior: temperature, structural relaxation, and alloy composition. The goal is to develop a detailed, realistic model of the mechanism by which a region of distributed plastic deformation develops around a crack tip. The second major aspect of this program will be to explore how the elastic properties and the shear modulus in particular, are influenced by anelastic atomic rearrangements. PI seeks to correlate observed changes in structure under load with measured changes in the elastic constants, under the influence of temperature, relaxation, and composition. PI will also connect this behavior to structure through detailed ex situ characterization, including resonant x-ray scattering and fluctuation electron microscopy. By understanding the ways in which atomic rearrangements (which may be connected to plastic deformation) influence the shear modulus PI can begin to understand the connection between elastic properties and fracture at a fundamental level. NON-TECHNICAL: The research program will advance the education and training of graduate students, undergraduate students, and local high school students by integrating them into a research team that includes the PI and the other members of his research group. The results of the basic scientific research will be disseminated via journal publications, conference and seminar presentations (by the undergraduate and graduate students as well as the principal investigator), and the web. High school students, including some from under-represented groups, will participate through a cooperative program with Project Ingenuity at Baltimore Polytechnic High School.

技术支持：块体金属玻璃联合收割机结合了金属的一些突出的机械性能，包括高强度和刚度，以及玻璃的加工灵活性。然而，它们确实有一个显着的局限性，因为塑性变形局部化到剪切带中会导致小塑性应变下的断裂，特别是在张力下。然而，一些金属玻璃是相当坚韧的（断裂能类似于高强度晶体合金的断裂能），而另一些则是真正易碎的。这种差异的起源还不清楚。了解的基本物理机制负责将是一个重要的贡献，新合金的发展与改善韧性和损伤容限。PI试图通过一项结合实验和计算技术的研究计划来解决这一挑战，以探索金属玻璃塑性变形和断裂之间竞争的基本方面。最近观察到的弹性性能和断裂能之间的相关性是理解结构和断裂之间关系的一个潜在有用的环节。PI将详细研究脆性断裂和塑性流动之间的竞争。这项工作的核心将是详细的结构表征的塑性区周围的裂纹尖端使用高能X射线散射在加载过程中进行原位。该技术允许测量金属玻璃中的弹性应变（以及应力），在结晶相和非晶相中具有优异的（~10 μ m）空间分辨率。这将使PI探索的条件下，剪切带开始附近的裂纹尖端。作为这项工作的一部分，PI将探索已知的三个变量的影响，以调解脆和坚韧行为之间的转变：温度，结构松弛，合金成分。我们的目标是开发一个详细的，现实的机制模型，通过该区域的分布塑性变形的裂纹尖端周围的发展。这个计划的第二个主要方面将是探索弹性性质和剪切模量，特别是如何受到非弹性原子重排的影响。PI试图在温度、松弛和成分的影响下，将在负载下观察到的结构变化与测量到的弹性常数变化相关联。PI还将通过详细的非原位表征将这种行为与结构联系起来，包括共振X射线散射和波动电子显微镜。通过理解原子重排（可能与塑性变形有关）影响剪切模量的方式，PI可以开始理解基本水平上弹性性质与断裂之间的联系。非技术性：该研究计划将通过将研究生，本科生和当地高中生整合到一个包括PI和他的研究小组其他成员的研究团队中，来推进研究生，本科生和当地高中生的教育和培训。基础科研的结果将通过期刊出版物、会议和研讨会报告（由本科生和研究生以及主要研究者）和网络传播。高中生，包括一些来自代表性不足的群体，将通过与巴尔的摩理工高中的项目合作计划参加。