Tian , L; Cheng, YQ; Shan, ZW; Li, J; Wang, CC; Han, XD; Sun, J; Ma, E,

1. Approaching the Ideal Elastic Limit of Metallic Glasses En (Evan) Ma, Johns Hopkins University, DMR 0904188 The ideal elastic limit is the upper bound to the stress and elastic strain a material can withstand. This intrinsic property has been widely studied for crystalline metals, both theoretically and experimentally. For amorphous metals, or metallic glasses (MGs), their ideal elastic limit remains poorly characterized and understood. We have shown that the elastic strain limit and the corresponding strength of submicron-sized MG specimens are about twice as high as the already-impressive elastic limit observed in bulk MG samples, in line with simulation predictions. At room temperature, the proportionality limit is found to be 3.3% and the total recoverable strain is 4.4%, compared with ~2% of bulk MG samples. We achieved this measurement by employing an in situ transmission electron microscopy tensile deformation technique. The ultimate limit found is of obvious interest because one of the most attractive attributes of MGs is their high strength (2 to 5 GPa) and large elastic strain, rendering them very appealing for applications requiring high load-bearing capacity and/or involving the storage of elastic energy. The very strong and elastic (submicron) “whiskers” we used are very interesting for applications in MEMS and NEMS devices. Stress-strain curve obtained from quantitative in situ tensile test inside a TEM: note the high stress levels and large recoverable (elastic) strains. TEM images from the movie recorded during the tensile test of submicron specimen: the strains measured are marked for the gauge length between the two markers • Tian, L; Cheng, YQ; Shan, ZW; Li, J; Wang, CC; Han, XD; Sun, J; Ma, E, • Approaching the ideal elastic limit of metallic glasses, Nature Communications3 (2012) 609 DOI: 10.1038/ncomms1619

2. Approaching the Ideal Elastic Limit of Metallic Glasses En (Evan) Ma, Johns Hopkins University, DMR 0904188 For the work discussed here, the notable broader impact is the strong international collaboration component. The quantitative in situ tensile test is the best in the world for metallic glasses, and was made possible through a collaboration with Prof. Z.W. Shan’s group at Xi’an Jiaotong University in China. A new procedure was developed to deposit carbon as markers for the gauge length, to allow accurate monitoring of small strains. The submicron specimens were made by using focused ion beam micromachining, as shown in panel (a). The gauge section (red box in (b) was marked using deposited carbon, as shown in (c). The technical knowhow for this procedure was developed by Prof. Z.W. Shan’s group at Xi’an Jiaotong University in China. The collaboration not only made this work possible, but also benefited both sides in training graduate students and making the best use of the state-of-the-art instruments for research on cutting edge nanomechanics ideas. The success of this project will have impact on sustaining a long-term future collaboration with Xi’an Jiaotong University.