-------------------------------------------------------------------- COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER College of Science (CDS Department CSI 898-Sec 001) -------------------------------------------------------------------- Plastic Flow of Amorphous Metals: Insights from In-situ Transmission Electron Microscope Measurements Evan Ma Department of Materials Science and Engineering Johns Hopkins University, Baltimore, MD 21218 The metals and alloys we are familiar with are all crystalline and well understood. In contrast, their recently emerged amorphous counterparts, i.e., "bulk metallic glasses" (BMGs), pose new challenges to the materials science community. Here even the basic issues, such as why they are such easy glass formers, how atoms pack inside, and how plastic deformation proceeds in the absence of well-defined dislocations, have not been resolved. We report in situ nano-compression and nano-tensiton tests of metallic glasses (MGs) in a transmission electron microscope. This new technique is capable of spatially and temporally resolving the plastic flow in MGs. The observations reveal the intrinsic ability of monolithic MGs to sustain large plastic strains (with gradual necking in tension as known for ductile crystalline metals), which would otherwise be pre-empted by catastrophic instability in macroscopic samples and conventional tests. The high ductility in volume-limited MGs, and the sample size effects in suppressing the rapid failure common to glasses, is explained by considering the evolution of the collectivism of flow defects towards localization. Monday, March 17, 2008 4:30 pm Room 301, Research I, Fairfax Campus Refreshments will be served at 4:15 PM. ---------------------------------------------------------------------- Find the schedule at www.cmasc.gmu.edu/seminar/schedule.html --------------------------------------------------------------------