Nanoscale patterning in alloy systems under driving forces

1
Nanoscale patterning in alloy systems under
driving forces
OUTLINE I/ Examples of patterning in alloys
driven by shear or irradiation II/ Driven
systems competing dynamics... III/ with
different length scales IV/ Challenges and
potential applications
2
I.1/ Compositional patterning in ball-milled
Cu50Ag50

• Stable steady-statesfor various milling T
• at liquid nitrogen
• Forced mixing of immiscible
• elements into a solid solution
• at 230C
• Decomposed with l  30 nm

EDS/STEM chemical map Cu and Ag
(S Zghal, R. Twesten, F. Wu, P. Bellon, Acta
Mater 2002.)
3
I.2/ Patterning of chemical order in
Ni-13.5Alinduced by ion-beam processing
Nelson et al, J. Nucl. Mater 44, 318 (1972)
/ Ni-13.5 at Al alloy irradiated with 100keV
Ni ions at 550 C, up to 100 dpa, undergoing
inverse coarsening(dark ield image of ordered
precipitates)
Patterns of ordered (L12) and disordered (A1)
phases
Origin of the patterns?
/ Additional recent evidence dppt2nm Ni-12 at
Al, 300 keV Ni at 550C G. Schmitz et al., PRB
63, 224113 (2001)
4
II.1/ Driven systems competing dynamics... (G.
Martin, Phys. Rev. B 1984)

• Binary alloy under irradiation thermal
  ballistic diffusion
• Effective free energy f
• f (c) Regular solution
• Effective temperature criterion
• Effective interaction criterion

No patterning
5
III.1/ with different length scales
Irradiation Plastic deformation L from a
few atoms for EPKA 25-100 eV L the grain
size to 104 atoms for EPKA 10 keV and
above (macroscopic) R mostly nearest
neighbor relocations, R 1 to 100 b but
medium to long range tail (nm) mixing from MD
simulations, mixing random in Cu-Ag
random mixing if DHmixlt0 or moderately
positive (Cu-Ag),
6
III.2/ Irradiation w/ finite length ballistic
jumps, RR. Enrique, PRL 00, PRB 01, APL01,
JAP 03

• wR(x) distribution of ballistic exchanges
• R average relocation length

Distribution of ballistic atomic relocations
along a crystallographic direction, during an
irradiation event.
7
III.3/ Dynamical phase stabilityfrom dynamics
to effective interactions

• Express concentration field by conserved order
  parameter ?(x) c(x) - 1/2

• Where, for thermal diffusion

• Yielding the governing equation

• Reformulate the problem in terms of an effective
  free energy E

and
with
8
III.4/ Analytical steady-state phase diagramfor
alloys under irradiation effect of relocation
length R
Patterning whenR gt Rc and g1 lt g lt g2
R average relocation distance
Insets steady-state Kinetic Monte Carlo
simulations, R 5 ann,(111)cuts.
R.A. Enrique and P. Bellon, Phys. Rev. Lett. 84,
2885 (2000).
g G/M normalized frequency of ballistic
exchanges
9
III.5/ Fluctuations in solid solutionEquilibrium
case
H. E. Cook, Acta Met. 18 297 (1970)
Fourier transform, linearize around
J. S. LangerAnnals Phys. (1971, 1973)
10
III.6/ Structure factor with 2 dynamics in
parallelgeneralized effective interactions
Generalized effective temperature for driving
force and fluctuations
11
III.7/ Irradiation w/ finite cascade size, L
Stoichiometric ordered alloy (TltTc)irradiated
with energetic heavy ions-gt disordered zones
L
Four ordering variants
12
III.8/ KMC steady-state phase diagramfor alloys
under irradiation effect of cascade size b (L)
2b number of atoms in cascade
L12 stoichiometric alloy ( Ni3Al)
Patterning (OP) whenL gt Lc and g1 lt g lt g2
g G/M normalized frequency of ballistic
exchanges
Jia Ye and P. Bellon (2003)
13
III.9/ Alloys under shear3D kinetic Monte Carlo
simulations.

• External forcing Random shearing in 111 along
  lt110gt at rate Gsh
• High T, low Gsh Moderate T, Gsh Low T, high
  Gah
• Kinetic roughening Mesoscopic phase Solid
  solution (Tunable wavelength)

L
P. Bellon, RS Averback, Phys. Rev. Lett. 74, 1819
(1995).
14
III.10/ Summary on irradiation- or shear-induced
patterning

• Dynamical Self-Organization Competing dynamics
  operating at different length scale can
  stabilize tunable nanoscale patterns.
• Kinetic modeling
• - Driving forces Effective free energies or
  effective interactions- Quantitative agreement
  with atomistic simulations (KMC)
• Effect of external length scales on patterning

15
IV.1/ Characterization of Cu-Ag
nanocompositesthree-dimensional atom probe
microscopy
20 nm
Milled at 150 C Decomposed ( 3 nm), diffuse
interfaces
Milled at 180 C Decomposed (5nm), interfaces
becoming sharp
Milled at 120 C Solid solution w/ some
clustering
F. Wu, P. Bellon, D. Isheim, D.N. Seidman, in
preparation
16
IV.2/ Potential applications and more examples

• Superhard electrical conductors,
• (Cu-Ag -gt 6 GPa)
• or coatings
• Megajoule permanent magnets
• (Sun et al, Nature 2002)
• Void lattice formed
• by irradiation (Loomis)
• Dislocation patterning induced by
  plastic deformation (Jäger)

17
Nanoscale patterning in alloy systems under
driving forces
OUTLINE I/ Examples of patterning in alloys
driven by shear or irradiation II/ Driven
systems competing dynamics... III/ with
different length scales IV/ Challenges and
potential applications