CAREER: Reversible plasticity in nanocrystalline metals and alloys for shape memory applications

非技术描述：纳米晶材料是由平均尺寸约为100纳米或更小的晶体（颗粒）组成的。小晶粒尺寸导致非常高的强度，这导致了使用这些材料的结构应用的显著兴趣。除了超强的强度外，纳米晶材料还表现出一些有趣的特性，包括恢复塑性变形的能力，而塑性变形通常被认为是不可恢复的。该职业奖支持的基础研究旨在利用纳米晶体金属和合金中这种不寻常的变形恢复，用于形状记忆相关应用。从本质上讲，该项目为纳米晶体金属和合金作为智能、功能性材料在航空航天、医学和机器人领域的应用奠定了基础。该研究活动与在多个层面上促进材料科学教育的广泛努力相结合。这些教育和推广工作包括一项新的指导计划和针对高中生的科学演示、教师研讨会、课程改进以及对本科生和研究生进行多学科材料研究的培训。技术说明：通常，塑性变形被认为是永久性的。而纳米晶材料在热活化卸载后可以恢复大部分塑性应变。该项目探索了这种不寻常的应变恢复的基本方面，并试图确定是否可以通过控制纳米晶金属和合金的微观结构来重复获得完全的应变恢复。研究的目标有两个：1)表征纳米晶面心立方金属和合金在多个循环过程中应变恢复的可重复性和温度依赖性；2)了解材料性能（弹塑性各向异性、层错能）和微观结构非均质性（晶粒尺寸和取向的变化）之间的相互作用如何影响应变恢复特性和机制。这些目标是通过新颖的微机电系统来实现的，该系统基于热机械测试和原位透射电子显微镜对具有可控微观结构的纳米晶金属和合金薄膜进行拉伸实验。

NON-TECHNICAL DESCRIPTION: Nanocrystalline materials are composed of crystallites (grains) that have an average size of about 100 nanometers or less. The small grain size leads to very high strength, which has led to significant interest in using these materials for structural applications. But in addition to their exceptional strength, nanocrystalline materials also exhibit several intriguing properties including the ability to recover plastic deformation, which is typically considered to be irrecoverable. This CAREER award supports fundamental research that aims to exploit this unusual deformation recovery in nanocrystalline metals and alloys for shape memory related applications. In essence, the project lays the foundation to employ nanocrystalline metals and alloys as smart, functional materials that have applications in aerospace, medicine and robotics. The research activity is integrated with a broad effort to promote materials science education at multiple levels. These education and outreach efforts include a new mentoring program and scientific demonstrations for high school students, teacher workshops, course enhancements, and training of undergraduate and graduate students in multidisciplinary materials research. TECHNICAL DESCRIPTION: Conventionally, plastic deformation is considered to be permanent. However, nanocrystalline materials can recover a large fraction of plastic strain after unloading by thermal activation. This project explores the fundamental aspects of this unusual strain recovery and seeks to determine whether complete strain recovery can be repeatedly obtained in nanocrystalline metals and alloys by controlling their microstructure. The research efforts are directed towards two distinct goals: 1) Characterizing the repeatability and temperature dependence of strain recovery in nanocrystalline face centered cubic metals and alloys over multiple cycles and 2) Understanding how the interplay between material properties (elastic and plastic anisotropy, stacking fault energy) and microstructural heterogeneity (variation in size and orientation of grains) affects the strain recovery characteristics and mechanisms. These goals are pursued using novel, micro-electro-mechanical systems based thermomechanical testing and in situ transmission electron microscopy straining experiments on nanocrystalline metal and alloy films with controlled microstructures.