Nanoscale Order in Metallic Glass

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Nanoscale Order in Metallic Glass
Paul M. Voyles, University of Wisconsin- Madison
, DMR 0347746
Primary Al crystallization in Al-based metallic
glasses offers a unique window into nucleation
and crystallization. We have previously used
fluctuation electron microscopy, a novel
technique for measuring order in glasses, to show
that rapidly quenched Al-glass contains crystal
nuclei frozen into the structure 1, offering a
snapshot of the earliest stages of nucleation.
Annealing after quenching allows those nuclei to
grow, but only to 10 nm in diameter before
out-diffusion of the rare-earth component limits
growth. We have now shown that substituting 1
at. Cu for Fe in Al88Y7Fe5 changes both the
distribution of quenched in nuclei and the
resulting crystallized microstructure. Adding Cu
increases the number density of nuclei at
approximately the same size. After annealing,
this results in an increase in the number density
of crystals and a reduction in their size. This
required developing a new model of the
fluctuation microscopy signal for this system,
and represents a complete structural
understanding of a new microstructure control
path. 1 W. G. Stratton et al. APL 86, 141910
(2005).
As-quenched Adding Cu decreases V(k), a measure
of the nanometer-scale spatial heterogeneity by
increasing the number density of quenched-in
nuclei.
Crystallized Adding Cu increases the number
density and decreases the size of nanocrystals.
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Nanoscale Order in Metallic Glass
Paul M. Voyles, U. Wisconsin, DMR 0347746
Training the Nanotechnology Workforce To support
education in advanced microscopy techniques using
TEM and STEM, Voyles has created the Electron
Microscopy Database (EMdb), a web clearinghouse
for high-quality educational examples. Most
teaching examples come from research, and not
every teacher has the ongoing research to provide
good examples for every technique. EMdb is a way
for teachers to exchange examples, including
possible exercises, and a way for researchers to
leverage their unpublished results for impact in
the classroom. Since its announcement at the
meeting Microscopy and Microanalysis Aug 5-8,
2007, over 200 users have registered to access
EMdb, and three research groups have submitted
examples for dissemination.