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
