When 3:30 PM - 5:00 PM Oct 21, 2011
Where 1670 CSE
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Takeshi Egami, Materials Science and Engineering, University of Tennessee/Oak Ridge National Lab


Mechanical Failure of Metallic Glasses: An Atomistic View

Metallic glasses show very high mechanical strength, and are promising as structural materials.  However, the microscopic mechanism of failure is not known.  People generally assume that failure occurs because of some defects, such as free-volume or shear transformation zones, by extrapolating our knowledge of the crystalline state.  If that is the case the strength should depend sensitively on details of the structure and composition, as in crystalline materials, whereas the yield strain of a metallic glass is always about 2%.  I propose a rather different view, that the concept of defects is irrelevant, and the failure is a part of the nature of the glassy state itself.  It is possible to define defects as unstable atomic sites, but in this case the concentration of defects is about 25%, far larger than those in crystalline materials.  Failure is the stress-induced glass transition which can occur without heating or volume dilation.  This view is supported by the results of molecular dynamics simulation and x-ray diffraction. 

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