Nanoscale SelfOrganization of Metallic Alloys under Ion Irradiation Robert Averback and Pascal Bello

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Nanoscale Self-Organization of Metallic Alloys
under Ion IrradiationRobert Averback and Pascal
Bellon, University of Illinois, MET DMR Award
0407958
DMR METALS RESEARCH PROGRAM
Motivation for the research Alloys are subjected
to external forcing in a number of situations
wear, fatigue, ball milling and energetic
particle irradiation, and it has been observed
that these alloys can be driven far from their
equilibrium phases. Theoretical efforts to
understand these phenomena1 have led to the
construction of dynamic phase diagrams like the
one shown below. Here the dynamical variables
are, R, the distance over which atoms are forced
to move by the driving forces (i.e. shearing, or
irradiation), and g, the ratio of forced jumps to
thermally activated jumps. Our experiments are
designed to test these theoretical concepts and
aid in their development. We use ion beam
irradiation since the variable R and ? can be
carefully controlled.
Significant findings Our experiments employ thin
films of the eutectic alloy, Cu85Co15, subjecting
them to 1.8 MeV Kr irradiation at different
temperatures.2 This procedure samples the trace
through the phase diagram, indicated by the red
line. We use the superparamagnetic behavior of
small Co particles to determine the precipitate
size. As shown in the figure below, we find that
at irradiation temperatures below 300 C, the
precipitates reach a steady state size,
illustrating the patterning regime in the dynamic
phase diagram. By raising the temperature above
350 C, decreasing ?, the growth of the
precipitates does not saturate, indicating that
the system has crossed into the regime of
macroscopic phase separation, or coarsening. This
work thus confirms the theoretical predictions,
and it has begun to determine the phase
boundaries in a real alloy.
References 1. R. Enrique and P. Bellon, PRL 84,
2885 (2000). 2. P. Krasnochtchekov, R.S.
Averback and P. Bellon, Phys. Rev. B (in press)
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Nanoscale Self-Organization of Metallic Alloys
under Ion IrradiationRobert Averback and Pascal
Bellon, University of Illinois, MET DMR Award
0407958
DMR METALS RESEARCH PROGRAM
Broader impact The current and future
experiments of this research aim at providing
critical tests of concepts and models developed
in the so-called driven alloy framework. The
present results provide direct evidence for
compositional patterning induced by ion-beam
processing, in agreement with model predictions.
Because these findings are quantitative they can
be directly extrapolated to other external
forcing situations, and they should also be of
enormous help in designing materials for nuclear
energy applications. PB is currently writing a
chapter on the Relaxation on nonequilibrium
alloys for a book entitled Alloys Physics (Ed.
W. Pfeiler, pub. Wiley VCH), which will highlight
these results. PB has also submitted a proposal
to the MRS to organize in fall 2006 a symposium
on a theme that includes the present research
Thermodynamics and kinetics of phase and
microstructural evolution.

• A Materials Van to bring materials science
  demonstrations to local high schools
• The two graduate students supported by the grant
  as well as two female undergraduates from our
  Department have identified and prepared 10
  materials science demonstrations that will be
  presented this fall to a science class (11th
  grade) at a local high school
• work hardening of an aluminum strip
• heat treating and quenching of a piano wire
• shape memory alloys
• bulk amorphous metals for golf club heads
• heat resistance of a ceramic tile
• gelation of polyvinyl alcohol
• synthesis of nylon
• magnetic levitation with a high-Tc
  superconductor
• conduction of light by optic fiber
• grain boundary decohesion of Al by Ga wetting
• Several local high schools have also been
  contacted and are interested in scheduling a
  visit from our Materials Van.