Special Materials Science & Engineering Seminar
Date: April 23, 2014 from 11:00 am to 12:00 pm EDT
Location: Columbia University, Morningside Heights,
210 Mudd (APAM Conference Room)
Contact: For further information regarding this event, please contact APAM Department by sending email to seasinfo.apam@columbia.edu or by calling 212-854-4457.
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Lisa Chen (Materials Science, Columbia University, B.S. '08)
University of Pennsylvania

"Investigating Thermally Activated Incipient Plasticity in Pd Nanowhiskers"

While plastic deformation in bulk FCC metals is primarily mediated by dislocation motion and interactions, single-crystal nanostructures lacking pre-existing dislocations or dislocation sources must rely on other mechanisms such as dislocation nucleation. Several experiments have demonstrated this phenomenon at room temperature, but challenges remain in quantitatively evaluating the barriers for nucleation as well as the associated scatter in the measured yield strengths. In particular, dislocation nucleation is predicted to be thermally activated and thereby much more sensitive to parameters such as temperature than incipient plastic flow in bulk systems. To investigate the presence of thermally activated processes, tensile tests on nominally defect-free single-crystal Pd nanowhiskers have been performed over a range of strain rates (10-5 to 10-3/s) and temperatures (100K to 475K).  The resulting mechanical response during in situ SEM and TEM testing and temperature testing in a controlled cryostat environment are coupled with a theoretical framework to enable the quantification of relevant thermal activation parameters.

Joint work with Jungho Shin a, Soraya Terrab a, b, Gunther Richter c, John P. Sullivan d, Daniel S. Gianola a 

a Department of Materials Science, University of Pennsylvania
b Department of Physics, Bryn Mawr College
c Max Planck Institute for Intelligent Systems
d Center for Integrated Nanotechnologies

Host: I.C. Noyan