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           COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
                             College of Science
                      (CDS Department CSI 898-Sec 001)
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    "Atomic-Level Structure and Its Evolution in Metallic Glasses"
                       Hongwei (Howard) Sheng
Department of Materials Science and Engineering, Johns Hopkins University

Metallic glasses, owing to their extraordinary physical properties (high
strength, good formability in the supercooled liquid state, excellent
corrosion resistance, etc.), are emerging engineering materials of current
research interest. Unlike the well-defined long-range order that characterizes
crystalline metals, the atomic arrangements in these amorphous metals remain
mysterious at present. Despite intense research activities on metallic glasses
and relentless pursuit of their structure description, the details of how the
atoms pack themselves in amorphous metals are not well-understood. In this
talk, by using a combination of state-of-the-art experimental and
computational techniques, I will present a general picture regarding the
atomic packing schemes in metallic glasses (Sheng et al., Nature, 2006):
distorted but quasi-equivalent clusters (Kasper polyhedra) are the dominant
building motifs, and they efficiently pack space in an icosahedral-like manner
to form the medium-range-order (~1 nm). The implication of this discovery will
be illustrated through a detailed analysis on the structure and forming
ability of Al-based glasses. Next, I will focus on the evolution of atomic
packing in metallic glasses as a function of thermodynamic variables (e.g.,
temperature and pressure), and relate it to outstanding problems in glass
science such as glass transition, deformation mechanism, and phase transition.
In particular, a new phase transition in metallic glass ⓠpolyamorphism
ⓠwill be introduced, where a metallic glass is induced by hydrostatic
pressure to transit between two different amorphous states (Sheng et al.,
Nature Materials, 2007). 
  
                          Febraury 12, 4:30 pm
                   Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at http://www.cmasc.gmu.edu/seminar/schedule.html
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