CAREER: Understanding Kirkendall Pore Formation and Evolution: Correlating Compositional, Geometrical, and Thermal Influences

职业：了解柯肯德尔孔隙的形成和演化：关联成分、几何和热影响

• 批准号: 2143334
• 负责人: Ashley Paz y Puente
• 金额: $ 50.71万
• 依托单位: University of Cincinnati Main Campus
• 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=2143334&HistoricalAwards=false
• 关键词: CAREER; Understanding; Kirkendall; Pore; Formation

PART 1: NON-TECHNICAL SUMMARY When you wake up in the morning to the smell of bacon or watch food coloring spread in water you are appreciating diffusion. In general terms, diffusion is the movement of things from areas of higher concentration to areas of lower concentration. Even though it is not obvious at room temperature, diffusion is happening in the solids around us as well - just at much slower speeds than what we witness when we smell something in the air or see something spread in water. Because certain types of atoms diffuse at higher rates than others, they can leave behind empty spaces called vacancies. If there are enough vacancies near one another in a material, they can merge and form pores. Typically, scientists try to avoid porosity in a material because it can decrease the mechanical, electrical or thermal properties especially when pores occur near a surface. Interestingly, it was discovered in the 1940's that diffusion in solids could be carefully controlled and as a result, influence where porosity in a material is located. This discovery is called the "Kirkendall effect" and it can be used to intentionally tailor the location of pores in a material so they become beneficial. Hollow structures for example can have several advantages in applications ranging from batteries to biomedical implants. This project supports fundamental research to determine how composition, geometry, and temperature influence the movement of vacancies and the evolution of these "Kirkendall" pores. By understanding the effect of composition, geometry and temperature we can design better materials that either eliminate porosity if harmful to the material or use them to create useful structures if advantageous for a given application. This project also includes a significant educational component that focuses on exposing students to, and engaging them in, materials science across high school, undergraduate and graduate levels. Through both recruiting and outreach activities integrated with this project, broadening participation of traditionally underrepresented groups in STEM will be emphasized to help diversify the engineering careers talent pool for years to come. PART 2: TECHNICAL SUMMARY This CAREER project aims to further understanding and control of vacancy-induced migration via the Kirkendall effect while engaging in multiple education and outreach activities to profoundly impact students in high school, undergraduate study and at the graduate level. The overall research goal is to systematically investigate the compositional, thermal and geometric influences on vacancy migration and Kirkendall pore evolution. Specifically, the three research objectives are to (i) evaluate the effect of Cr additions, (ii) assess the role of radial symmetry and aspect ratio and (iii) determine the magnitude of temperature gradient required for Kirkendall pore coalescence in Ni-Cr-Al-Ti based systems. These objectives are accomplished via experiments involving the fabrication and analysis of diffusion couples and diffusion coated micro-objects via conventional ex-situ metallography and 4-D microstructural characterization enabled by in-situ X-ray tomography. The broader impacts of this work are to help produce a diverse STEM-capable workforce for various career pathways by incorporating central concepts addressed in this project into education and outreach activities that expose and engage students in materials science. The education and outreach activities center on the following three education objectives: (i) expanding a Materials Camp for high school students and teachers (ii) enhancing a “How It’s Made” hands-on undergraduate honors seminar course, and (iii) creating innovative diffusion modules to enable flipped classes for materials science graduate students.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.

当你早上醒来闻到熏肉的味道，或者看着食用色素在水中扩散时，你正在欣赏扩散。一般来说，扩散是物质从浓度较高的区域向浓度较低的区域的运动。尽管在室温下并不明显，但扩散也在我们周围的固体中发生——只是扩散的速度比我们闻到空气中的气味或看到水中扩散的速度慢得多。因为某些类型的原子比其他类型的原子扩散速度更快，所以它们会留下被称为空位的空白空间。如果在一种材料中有足够的空位，它们就可以合并并形成孔。通常情况下，科学家们试图避免材料中的孔隙，因为它会降低机械、电气或热性能，特别是当孔隙出现在表面附近时。有趣的是，在20世纪40年代，人们发现可以仔细控制固体中的扩散，从而影响材料孔隙率的位置。这一发现被称为“Kirkendall效应”，它可以用来有意地调整材料中孔隙的位置，使它们变得有益。例如，中空结构在从电池到生物医学植入物的应用中具有若干优点。该项目支持基础研究，以确定成分、几何形状和温度如何影响空位的运动和这些“Kirkendall”孔隙的演化。通过了解成分、几何形状和温度的影响，我们可以设计出更好的材料，如果对材料有害，可以消除孔隙，如果对特定应用有利，可以使用它们来创建有用的结构。该项目还包括一个重要的教育组成部分，重点是让学生接触并参与高中、本科和研究生阶段的材料科学。通过与该项目相结合的招聘和推广活动，将强调扩大传统上代表性不足的群体在STEM中的参与，以帮助在未来几年实现工程职业人才库的多样化。本职业项目旨在通过Kirkendall效应进一步了解和控制空缺导致的移民，同时参与多种教育和推广活动，深刻影响高中、本科和研究生阶段的学生。总体研究目标是系统地研究组分、热因素和几何因素对空位迁移和Kirkendall孔隙演化的影响。具体来说，这三个研究目标是：(i)评估Cr添加的影响，（ii）评估径向对称和纵横比的作用，（iii）确定Ni-Cr-Al-Ti基体系中Kirkendall孔隙聚结所需的温度梯度的大小。这些目标是通过实验来实现的，包括通过传统的非原位金相和原位x射线断层扫描的4-D显微结构表征来制造和分析扩散偶和扩散涂层微物体。这项工作的更广泛的影响是，通过将本项目中涉及的核心概念纳入教育和推广活动，使学生接触和参与材料科学，帮助培养具有stem能力的多样化劳动力，以适应各种职业道路。教育和推广活动以以下三个教育目标为中心：(i)为高中学生和教师扩大材料营；（ii）加强“如何制造”实践本科荣誉研讨会课程；（iii）为材料科学研究生创建创新的扩散模块，使翻转课堂成为可能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。