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

非技术描述：纳米晶体材料由平均尺寸约为100纳米或更小的微晶（晶粒）组成。小晶粒尺寸导致非常高的强度，这导致了对将这些材料用于结构应用的极大兴趣。但除了其特殊的强度，纳米晶材料还表现出几个有趣的特性，包括恢复塑性变形的能力，这通常被认为是不可恢复的。这个职业奖支持基础研究，旨在利用这种不寻常的变形恢复纳米晶金属和合金的形状记忆相关的应用。从本质上讲，该项目为将纳米晶金属和合金用作智能功能材料奠定了基础，这些材料可应用于航空航天，医学和机器人技术。研究活动与广泛的努力相结合，以促进多层次的材料科学教育。这些教育和推广工作包括一个新的指导计划和高中学生的科学演示，教师研讨会，课程改进，以及多学科材料研究的本科生和研究生的培训。技术描述：通常，塑性变形被认为是永久性的。然而，纳米晶材料可以通过热激活在卸载后恢复大部分塑性应变。该项目探讨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其微观结构在纳米晶金属和合金中重复获得完全的应变恢复。研究工作针对两个不同的目标：1）表征纳米晶面心立方金属和合金在多个循环中应变恢复的可重复性和温度依赖性，以及2）理解材料特性之间的相互作用（弹性和塑性各向异性，层错能）和显微结构不均匀性（晶粒尺寸和取向的变化）影响应变恢复特性和机制。这些目标是追求使用新的，微机电系统为基础的热机械测试和原位透射电子显微镜应变实验纳米晶金属和合金薄膜与控制的微观结构。

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.