in-situ observations of moving interfaces during dp reaction · matrix pfz α lamella b....
TRANSCRIPT
1.1. SteadySteady state growthstate growth-- regularregular morphologymorphology
1.1. 1.1. OverallOverall viewview
1.2. 1.2. SoluteSolute concentrationconcentration profilesprofiles
1.2.1. 1.2.1. AcrossAcross thethe reactionreaction frontfront
1.2.2. 1.2.2. AcrossAcross thethe αααααααα lamellalamella
Paweł Zięba – Chemical and kinetic characterization of diffusional…
In-situ observations of moving interfaces during DP reaction
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2. 2. SteadySteady state growthstate growth-- irregularirregular morphologymorphology
2.1. 2.1. ChangesChanges of of thethe reactionreaction front front shapeshape
2.2. 2.2. ReRe--nucleationnucleation and and branchingbranching of of thethe ββββββββ lamellalamella
2.3. Stop2.3. Stop-- and go and go motionmotion ((oscillatoryoscillatory movementmovement))
3. Growth 3. Growth terminationtermination
3.1. 3.1. ImpingementImpingement of of coloniescolonies
3. 2. 3. 2. PrecipitatePrecipitate freefree zonezone
4. 4. SummarySummary, , unsolvedunsolved problemsproblems
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LT
αo
α β
vRF δ
λα
Paweł Zięba – Chemical and kinetic characterization of diffusional…
TheThe solutesolute redistributionredistribution occursoccurs atat thethe movingmoving RFRF
α+β
βα
xoA BxBxavxe
GB αo�α+β
ThereThere existsexists anan excessexcess ofof solutesolute atomsatoms withinwithin thethe αααααααα
lamellalamella comparedcompared toto thethe equilibriumequilibrium statestate
Nucleation
Paweł Zięba – Chemical and kinetic characterization of diffusional…
430 oC/0
460 oC/32 min
Fe-15 at.%Zn-C
E.P. Butler, V. Ramaswamy,
P.R. Swann, Acta Metall. 21
(1973-517-524.
470 oC/41 min
470 oC/45 min (DF)
470 oC/48 min
G.R. Purdy, N. Lange, in
Decomposition of Alloys:
the early stage, Proc. 2nd
Acta-Scripta Metallurgica
(P. Haasen, V. Gerold., R.
Wagner, M.F. Ashby- eds.),
Pergamon Press 1984, pp.
214-220
Al-28 at. % Zn: 105 oC±15 oC
STEADY STATE GROWTH – REGULAR MORPHOLOGY
Paweł Zięba – Chemical and kinetic characterization of diffusional…
STEADY STATE GROWTH – REGULAR MORPHOLOGY
Paweł Zięba – Chemical and kinetic characterization of diffusional…
Solute Distribution Across Reaction Front
20
30
at.
%]
RF
Paweł Zięba – Chemical and kinetic characterization of diffusional…
-200 -100 0 100 200
Distance [nm]
0
10
20
Zn c
on
ten
t [a
Matrix α lamella
Solute concentration profile across the α lamella
( )[ ]ooe x
Cyxxyx +
−−=
5.0cosh)()(
ins
Ds
vC
δ
λα2
=o
b
x
xs =
Paweł Zięba – Chemical and kinetic characterization of diffusional…
x(y)
λλλλαααα
y0 1
ooe xC
xxyx +−=)2/cosh(
)()(bDsδ ox
λλλλαααα
vinsRF
Shape changing
10
15
20
n c
on
tent
[at.
%]
0 s
50 s
90 s
Paweł Zięba – Chemical and kinetic characterization of diffusional…
0 s
50 nm
50 s 90 s
0.0 0.5 1.0
Spacing [arbitrary units]
5
Zn
α ββ
52o
41o
28o
73o
63o
48o
0.1 µm
Al-22 at.% Zn aged at 403 K.
K. Tashiro and G.R. Purdy:
Metall. Transactions A20 (1989) 1593.
RF RF shapeshape modellingmodelling (for (for knownknown solutesoluteconcentrationconcentration profile profile inin thethe αα phasephase lamellalamella
Paweł Zięba – Chemical and kinetic characterization of diffusional…
αβ β
49o
34o
34o
33o
23o
23o
0.1 µm
α
αα
αα
ρ
γc
m GM
vVo
o
∆−=
2
2
5.12
1
dy
zd
dy
dz
+
=ρ
( )( )
cosh,
)(C
ys
lxxxxy
−−= αλ
RF RF shapeshape modellingmodelling (for (for knownknown solutesoluteconcentrationconcentration profile profile inin thethe αα phasephase lamellalamella
Paweł Zięba – Chemical and kinetic characterization of diffusional…
( ) ( )2/cosh
,
)(Ceoo
lxxxxy
−−= αλ
∆G – local change of free energy at RF, M –RF mobility, Vm – molar volume of cellular
aggregate, γα/αο – α/αοinterfacial energy, r – local curvature of RF, v – growth rate
D. Duly, M.G. Cheynet, Y. Brechet:
Acta Metall. & Mater. 42 (1994) 3855.
cosθαα =0.1
γαβ=270 mJ/m2
cosθαα =0.4
γαβ=270 mJ/m2
cosθαα =0.707
γαβ=270 mJ/m2
cosθαα =0.707
γαβ=150 mJ/m2
y
yy
y
z
0.3
-0.3
-0.5 0.5
-0.5-0.5
-0.5
0.5
z
0.3
-0.3
zz
0.5
0.3 0.3
Paweł Zięba – Chemical and kinetic characterization of diffusional…
cosθαα =0.707
γαβ=400 mJ/m2
cosθαα =0.4
γαβ=400 mJ/m2
yy
-0.3 -0.3
-0.5 0.5-0.50.5
zz
-0.3-0.3
0.3 0.3
Mg-10 at.% Al aged at 493 K
D. Duly, M.G. Cheynet, Y. Brechet: Acta Metall. & Mater. 42 (1994) 3855.
ReconstructionReconstruction of of solutesolute concentrationconcentration profile profile inin thethe α α phasephase lamellalamella((fromfrom knownknown RF RF shapeshape))
α
αα
αα
ρ
γc
m GM
vVo
∆−=2
5.12
1
zd
dy
dz
+
=ρ [ ]oxxyRTG
)(2
−=∆ α
0 s
50 nm
50 s 90 s
For small solute content and small saturation (parabolic curve)
ααρcG
M o∆−=
2
2
dy
zdo
oc
xG
2=∆
[ ]2
22
)(5.0dx
GdxyxG c
oc
αα −=∆
)(yGc
α∆
x(y) xo
For small solute content (constant curvature)
Giibs free energy change
(thermodynamic data)
STEADY STATE GROWTH – IRREGULAR MORPHOLOGY
0 s
1
3
2�
1
2
3
12 sRe-nucleation
Paweł Zięba – Chemical and kinetic characterization of diffusional…
1
3B
2
3A
19 s
3A
3B
23 s
0.3 µm
30 s
45 s 90 s
33 s 0 s
Re-nucleation and branching
Paweł Zięba – Chemical and kinetic characterization of diffusional…
185 s � 200 s
240 s
0.4 µm
0 s
0.2 µm
15 s
20 s 35 s
Shape changing
Paweł Zięba – Chemical and kinetic characterization of diffusional…
400 s 310 s
65 s 105 s
160 s 265 s
6
8
10
en
t [a
t.%
]
b
Shape changing
Paweł Zięba – Chemical and kinetic characterization of diffusional…
0 100 200 300 400 500 600
Distance [µm]
4
6
Zn
con
te
Zmiana kształtu frontu reakcji
WZROST USTABILIZOWANY-MORFOLOGIA NIEREGULARNA
Oscillatory movement?
Paweł Zięba – Chemical and kinetic characterization of diffusional…
Stop- and go motion
oscillatory movement?
STEADY STATE GROWTH – IRREGULAR MORPHOLOGY
Paweł Zięba – Chemical and kinetic characterization of diffusional…
S. Abdou, G.I. Solorzano, M. El-Boragy,
W. Gust, B. Predel,
Scripta Mater. 34 (1995) 1431
Al-15 at.% Zn alloy: DP: 433 K
Impingement of colonies
0 s
C
A
B
0.4 µm
20 s
Paweł Zięba – Chemical and kinetic characterization of diffusional…
0 s 20 s
35 s 40 s
50 s 65 s
Precipitate free zone
a
A
A
0.1 µm
Paweł Zięba – Chemical and kinetic characterization of diffusional…
-80 -60 -40 -20 0 20 40
Distance [nm]
0
10
20
30
Zn c
onte
nt [a
t.%
]
Matrix α lamellaPFZ
b
A0.1 µm
Steady-state period of growth of DP reaction is influenced by variousinstabilities.
The system possesses some intrinsic capability to correct local RF shape tobalance the forces acting on it if the perturbation is not larger than a certaincritical value.
Paweł Zięba – Chemical and kinetic characterization of diffusional…
critical value.
This sensitivity of the system may result in some asymmetry of the soluteconcentration profile.
If the critical value is exceeded or simply perturbation imposed is too large,re-nucleation and branching phenomena occur.
In some cases system becomes to be unstable: non-steady state growth.
Termination of the DP reaction is due to impingement of colonies or PFZformation (backward migration of the RF).
There is no HREM in-situ observation: How the atomic transport at the RFreally looks like?
How to determine the solute profile across the αααα lamellae without a need forEDX/EELS analysis but based only on in situ recording of the RF shape?
What is the solute concentration profile within the RF from one to another
Paweł Zięba – Chemical and kinetic characterization of diffusional…
What is the solute concentration profile within the RF from one to anotherneighbouring ββββ lamella?
Paweł Zięba – Chemical and kinetic characterization of diffusional…