CAREER: Dislocation-level Understanding of Shear Banding in Magnesium and Magnesium Alloys

职业：对镁和镁合金中剪切带的位错水平理解

• 批准号: 2144973
• 负责人: Yu Kelvin Xie
• 金额: $ 46.45万
• 依托单位: Texas A&M Engineering Experiment Station
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-15 至 2027-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2144973&HistoricalAwards=false
• 关键词: CAREER; Dislocation; level; Understanding; Shear

PART 1: NON-TECHNICAL SUMMARYMagnesium (Mg) is a light-weight metal that is nearly four times lighter than steel, making it very attractive for automobile and aerospace applications. However, pure Mg and Mg alloys tend to crack fairly easily at room temperature. When Mg is stretched, it does not evenly distribute the strains it experiences. Instead, Mg tends to concentrate strains in localized zones called "shear bands". These shear bands become locations where Mg most often breaks and are responsible for why Mg cracks more easily than other metals. This project relates shear banding to the atomic level defects that occur in metals when they are stretched or deformed. These atomic level defects are called "dislocations". A greater number of dislocations that are more spread out are expected to promote more uniform deformation, or stretching of a material, and thereby delay shear banding. The insights gained from this work will help identify new Mg alloys that exhibit delayed shear banding, increased crack resistance and a greater ability for Magnesium metal to be formed into different shapes. The findings from this research will also help promote increased use of Mg across a wide variety of automotive and aerospace applications. Moreover, this project also produces interdisciplinary educational opportunities to train students in metallurgy, electron microscopy, and mechanics of solids. This project also provides a platform for professors and graduate students to work closely with underrepresented students through the Louis Stokes Alliances for Minority Participation program to expose them to the topics of this research project.PART 2: TECHNICAL SUMMARYMagnesium (Mg) alloys hold great potential for use as lightweight energy-saving materials, but the structural applications of Mg have been hindered by its low strain-to-failure properties at room temperature. The comparatively lower strain-to-failure exhibited by Mg as compared to other metals is chiefly related to the formation of localized shear bands. The goal of this work is to advance the understanding of deformation and failure mechanisms in Mg and its alloys and, in particular, discover pathways that trigger or delay plastic instabilities in them. The hypothesis examined here is that increased non-basal, c+a dislocation activities lead to more uniform deformation and provide more homogeneous strain hardening throughout the microstructure, hence delaying plastic instabilities by delocalizing shear bands in Mg and its alloys. The objectives of this work are to 1) identify the role of c+a dislocations on the formation of shear bands; and 2) identify the effect of temperature (up to 75 degrees Celsius) as well as alloying on c+a dislocation activities and shear band characteristics (e.g. size, number density, and stored plastic strain) in quasi-statically deformed Mg and Mg alloys. These objectives will be accomplished by experimentally measuring i) the stresses needed to operate dislocation sources, ii) the dislocation glide distances produced under given stresses, and iii) the related cross-slip frequency. These latter measures will then be directly correlated to the shear band characteristics mentioned in the second objective. The broader impacts of this project are two-fold. First, identifying pathways to more ductile and malleable Mg and Mg alloys will significantly enhance the opportunity and likelihood for Mg alloy usage across a variety of applications resulting in significant weight-savings and increases in energy efficiencies. Secondly, this project will facilitate increased educational engagement and outreach to students and persons within the collegiate environment and beyond through i) hands-on experiences for undergraduate students, ii) a digital platform to further undergraduate interest in materials science and iii) expansion of an existing YouTube channel engaging the general public on matters and phenomena related to materials science.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.

第 1 部分：非技术摘要镁 (Mg) 是一种轻质金属，比钢轻近四倍，这使其对汽车和航空航天应用非常有吸引力。然而，纯镁和镁合金在室温下很容易破裂。当镁被拉伸时，它所承受的应变不会均匀分布。相反，镁倾向于将应变集中在称为“剪切带”的局部区域。这些剪切带成为镁最常断裂的位置，也是镁比其他金属更容易断裂的原因。 该项目将剪切带与金属拉伸或变形时出现的原子级缺陷联系起来。这些原子级缺陷称为“位错”。更多分布的位错预计会促进材料更均匀的变形或拉伸，从而延迟剪切带。从这项工作中获得的见解将有助于识别新的镁合金，这些合金表现出延迟的剪切带、更高的抗裂性以及镁金属形成不同形状的更大能力。这项研究的结果还将有助于促进镁在各种汽车和航空航天应用中的使用。此外，该项目还提供跨学科教育机会，对学生进行冶金、电子显微镜和固体力学方面的培训。该项目还为教授和研究生提供了一个平台，让他们通过路易斯斯托克斯少数族裔参与联盟计划与代表性不足的学生密切合作，让他们了解该研究项目的主题。 第 2 部分：技术摘要镁 (Mg) 合金具有巨大的潜力作为轻质节能材料，镁的结构应用因其在室温下的低应变失效特性而受到阻碍。与其他金属相比，镁表现出相对较低的失效应变主要与局部剪切带的形成有关。这项工作的目标是增进对镁及其合金变形和失效机制的理解，特别是发现触发或延迟其中塑性不稳定性的途径。这里检验的假设是，非基础 c+a 位错活动的增加导致更均匀的变形，并在整个微观结构中提供更均匀的应变硬化，从而通过使镁及其合金中的剪切带离域来延迟塑性不稳定性。这项工作的目标是 1) 确定 c+a 位错对剪切带形成的作用； 2) 确定温度（高达 75 摄氏度）以及合金化对准静态变形镁和镁合金中 c+a 位错活动和剪切带特性（例如尺寸、数密度和储存塑性应变）的影响。这些目标将通过实验测量 i) 操作位错源所需的应力，ii) 在给定应力下产生的位错滑移距离，以及 iii) 相关的交叉滑移频率来实现。后面的这些测量将直接与第二个目标中提到的剪切带特征相关。该项目的更广泛影响有两个方面。首先，找到更具延展性和延展性的镁和镁合金的途径将显着增加镁合金在各种应用中使用的机会和可能性，从而显着减轻重量并提高能源效率。其次，该项目将通过 i) 为本科生提供实践经验，ii) 一个数字平台，以提高本科生对材料科学的兴趣，以及 iii) 扩大现有的 YouTube 频道让公众参与与材料科学相关的问题和现象。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。