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

智力优点：我们有实验证据表明，平均晶粒尺寸为50- 100 nm的塑性变形的多晶自立式薄金属膜在宏观无应力条件下恢复所有塑性应变（Science，（2007）315，pp 1831-34）。这一观察结果挑战了塑性应变是永久性的古老观点。当晶粒尺寸增大到100- 200 nm时，薄膜不再恢复塑性应变，但在卸载过程中仍表现出强烈的包申格效应。这些令人惊讶的和看似无关的现象，我们假设，是由微观结构的小尺寸尺度和其不均匀性（晶粒尺寸和取向变化）之间的相互作用。这个项目将探索这种相对未被探索的范式。它将研究应变恢复和Bauschinger效应在薄金属膜（铝，铜，Au和镍）的机制，通过定量的原位变形和退火研究的薄金属膜在透射电子显微镜（TEM）使用一种新的MEMS为基础的测试阶段。更广泛的影响：从该项目中获得的见解对于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，与国际科学家一起工作。该研究将以两种新的方式与教育相结合：（1）本科生小组将开发关于纳米材料的短视频;（2）来自加州理工学院（一所教学学院）的两名教师和4名学生将在暑假期间接受纳米材料培训。 该研究由国际科学与工程办公室（OISE）和工程理事会材料加工和制造计划（ENG/CMMI/MPM）共同资助

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