Interplay Between In-Homogeneity and Size Scale of Microstructure: A New Paradigm in the Mechanistic Exploration of Nano Grained Metal Deformation

智力优势：我们有实验证据表明，在宏观无应力条件下，平均晶粒尺寸为50-100 nm的塑性变形的多晶自支撑金属薄膜可以恢复所有的塑性应变(Science，(2007)315，pp1831-34)。这一观察结果挑战了古老的观点，即塑性应变是永久性的。当晶粒尺寸增加到100-200 nm时，薄膜不能恢复塑性应变，但在卸载过程中表现出很强的包辛格效应，但仍处于拉伸状态。我们假设，这些令人惊讶且看似无关的现象，是由微观结构的小尺寸尺度及其不均匀性(颗粒尺寸和取向变化)之间的相互作用所控制的。这个项目将探索这一相对未被探索的范例。利用一种新型的基于MEMS的测试平台，通过对金属薄膜(Al、Cu、Au和Ni)的原位形变和退火的定量研究，研究了金属薄膜(Al、Cu、Au和Ni)的应变恢复机制和包辛格效应。这项工作将与奥地利科学院联合进行。广泛的影响：从该项目中获得的见解将对开发纳米材料的计算/理论模型至关重要。参与该项目的学生将有难得的机会前往奥地利，与国际科学家合作。这项研究将以两种新的方式与教育相结合：(1)本科生小组将开发纳米材料短视频；(2)加州大学保利分校(一家教学学院)的两名教职员工和4名学生将在暑假期间接受纳米材料培训。这项研究是由国际科学和工程办公室(OISE)和工程局材料加工和制造计划(ENG/CMMI/MPM)共同资助的

Intellectual merit: We have experimental evidence showing that plastically deformed polycrystalline free standing thin metal films with average grain size of 50-100nm recover all of the plastic strain under macroscopic stress-free condition (Science, (2007) 315, pp 1831-34). This observation challenges the age-old view that plastic strain is permanent. When the grain size is increased to 100-200nm, the films do not recover plastic strain, but they show strong Bauschinger effect during unloading, while still under tension. These surprising and seemingly unrelated phenomena, we hypothesize, are governed by an interplay between the small size scale of the microstructure and its inhomogeneity (grain size and orientation variations). This project will explore this relatively unexplored paradigm. It will investigate the mechanism of strain recovery and Bauschinger effect in thin metal films (Al, Cu, Au and Ni) through quantitative in-situ deformation and annealing studies of thin metal films in Transmission Electron Microscope (TEM) using a novel MEMS based testing stage. The work will be conducted jointly with Austrian Academy of Science.Broader impact: The insight gained from the project will be essential to develop computional/theoretical models of nanomaterials. The students involved in the project will have the rare opportunity to travel to Austria and work with international scientists. The research will be integrated with education in two new ways: (1) groups of undergraduate students will develop short videos on nanomaterials; (2) Two faculty members and 4 students from Cal Poly (a teaching college) will be trained on nano materials during summer breaks. The research is co-funded by the Office of International Science and Engineering (OISE) and the Engineering Directorate Materials Processing and Manufacturing Program (ENG/CMMI/MPM