Characterization of Internal Oxidation - NISTcecamp/TMS2005/TMS 2005...0.05 0.2 0.5 0 B S O C K β=...
Transcript of Characterization of Internal Oxidation - NISTcecamp/TMS2005/TMS 2005...0.05 0.2 0.5 0 B S O C K β=...
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TMS 2005 --- Diffusion Symposium
Characterization of Internal Oxidation
Yali Li 1 and John E. Morral2
1 University of Connecticut, Storrs CT 06269 USA2 Ohio State University, Columbus OH 43210 USA
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Internal Oxidation Characterization
Cu-11%NiO2
unoxidized region
Internal oxidation region
Phases present --- XRDOxide fraction profile --- Image analysisConcentration profile --- EDXThickness of internal oxidation region
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Oxide Fraction Profile
Simulation results for saturated case in literature :
Rel
ativ
e ox
ide
frac
tion
Reduced distance
0
β→1
0.05
0.2
0.5
0B
SOCCK
=β
* E. K. Ohriner and J. E. Morral, Scripta Metallurgica, 13 (1979) 7.
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Oxide Fraction Profile
Experimental results in literature:
Fe-5%Cr
Fe-Cr alloys internally oxidized at 1000 °C for 20 hours with Po2=8.7×10-17atm.** O. Ahmed and D. J. Yong, Electrochemical Society Proceedings, 38 (1999) 77.
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Oxide Fraction Profile
Cu-7% Ni internally oxidized at 900° C in Rhines Pack
0
1000
2000
3000
4000
5000
10 30 50 70 90 110
Inte
nsity
NiOMatrix
2θ
XRD patternsSEM
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Oxide Fraction Profile
Image analysis: oxide area fraction profile
2µm
80µm
grey scale binary mode
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Oxide Fraction Profile
NiO area fraction versus distance
0 10 20 30 40 50 60 70 800
5
10
15
20
25
Distance from surface (micron)
Prec
ipita
te a
rea
perc
ent
Cu-7% Ni alloys internally oxidized at 900° C for 1 hour
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Oxide Fraction Profile
Simulation results: saturated case
0.00
0.25
0.50
0.75
1.00
0 0.4 0.8 1.2 1.6
=0.22 =0.03β β
Rel
ativ
e ox
ide
frac
tion
Reduced distance
DICTRA results0
β→1
0.050.2
0.5
Ohriner and Morral
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Oxide Fraction Profile
Simulation results: unsaturated case
Effect of β on relative oxide fraction profiles
x/x*
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
=0.001
=0.01
=0.1
=0.3
=0.5
=0.9
β
Rel
ativ
e ox
ide
frac
tion
β
β
ββ
β
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Oxide Fraction Profile
Summary:
When alloys are saturated with oxygen, oxide mole
fraction decreases asymptotically to zero and the position
of moving boundary cannot be defined.
When alloys are unsaturated with oxygen, the moving
boundary between internal oxidation region and
unoxidized region is well defined.
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Concentration Profiles
The classic model:
Moving boundary
Internal oxidation regionα(A+ dissolved O)+ BOν
Unoxidized regionα (A+ B)
Oxi
dizi
ngat
mos
pher
e
Assumptions:All the solute B is consumed to form BOv in the internal oxidation region.
The concentrations of dissolved B and O at the moving boundary are zero.
* C. Wagner, Z. Electrochem, 63 (1959) 772.
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Concentration Profiles
The classic model:O
xidi
zing
atm
osph
ere
Moving boundary
Internal oxidation regionα(A+ dissolved O)+ BOν
Unoxidized regionα (A+ B)
Distance from surface (x)
Con
cent
ratio
n
x*
αOC
αBC
BC
OC
0BC
SOC
ααBO CCK ×= = 0
* C. Wagner, Z. Electrochem, 63 (1959) 772.
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Concentration Profiles
Experimental results in literature:
Distance from surface (cm)
Haf
nium
( w
t% )
α+HfO2α
Nb-Hf alloy
* D. L. Corn et al. Oxidation of Metals, 35 (1991) 139
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Concentration Profiles
Concentration profiles under local equilibrium conditions
distance
α + β α
* W.J. Boettinger et al. Acta Metall.Mater. 48 (2000) 481-492.* J. E. Morral and H. Chen, Scripta Mater. 43 (2000) 699-703.
Matrix concentration profile, Ca,
is continuous in slope and value.
Average profile, , and
matrix profile, Cα, meet at the
moving boundary.
βα +C
Cα
Con
cent
ratio
n
Cα+β
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Concentration Profiles
The classic model versus Local equilibrium model
x*
0BC
Distance from surface (x)
Con
cent
ratio
n
αOC
Moving boundaryOxidized region Unoxidized region
αBC
BC
The classic model: BC αBC
K = 0
BC αBCLocal equilibrium model:
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Concentration Profiles
DICTRA simulation results: saturated case
0.00
0.05
0.10
0.15
0.0 1.0 2.0 3.0 4.0 5.00.000
0.005
0.010
0.015
Distance x ( ×10-4m )
Con
cent
ratio
n
CB (x)
CO (x)
Simulation conditions: β =0.96, DB/DO=10-3
2% oxide
Internal oxidation region
Unoxidized region
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Concentration Profiles
Concentration profiles of Cu-10% Ni alloys oxidized at 950 °C
-50 0 50 100 150 200 250 300 350 400 450 5000
2
4
6
8
10
12
3 hours 10 hours 30 hours
Ni%
in
mat
rix
Distance from surface (micron)
Estimated position of oxidation frontier
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Concentration Profiles
Error Function Model simulation results: unsaturated case
8.5
9.0
9.5
10.0
10.5
0.00 0.02 0.04 0.06 0.08 0.100.05
0.10
0.15
0.20
0.25
CB (x)
CO (x)
CB (x)
Con
cent
ratio
n
Reduced distance from surface ( λ )
moving boundary
Simulation conditions: β =0.96, DB/DO=10-3
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Concentration Profiles
Summary:
Concentration profiles in the classic model are in error because
they are not supported by experimental results in the literature
or in this study and have no theoretic basis.
When K = 0, there is no long-range diffusion of solute B, thus
the enrichment phenomena proposed by the classic model
doesn’t occur.
Near the boundary between oxidized and unoxidized region,
matrix solute concentration approaches initial solute
concentration rather than zero as assumed by the classic model.
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Thickness of Internal Oxidation Region
Cu-10%Ni alloys oxidized at 950 °C
3 hours
1 hour
10 hours
30 hours
Oxidation time (hour)
Thi
ckne
ss2
(×10
4µm
2 )
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35
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Thickness of Internal Oxidation Region
Cu-Ni alloys oxidized at 950 °C for 3 hours2.5% Ni
5.0% Ni
10.0% Ni
20.0% Ni0
2
4
6
8
0 10 20 30 40 50
Thi
ckne
ss2
(×10
4µm
2 )
01 NiC
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Conclusions (1)
For saturated cases:
(a) Because oxide fraction decreased asymptotically to zero, there
was no distinct boundary between the oxidized and
unoxidized regions.
(b) For DO>>DB, when oxide fraction approaches zero, matrix
solute concentration is close to initial solute concentration.
(c) DICTRA predicted internal oxidation under local equilibrium
for 0.03 < β < 0.22 for alloys saturated with oxygen.
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Conclusions (2)
For unsaturated cases:
(a) The moving boundary between internal oxidation region
and unoxidized region is well defined.
(b) For DO>>DB, solute concentration in matrix at the
moving boundary is close to initial solute concentration.
(c) When β → 1, Error Function Model can be used to
model internal oxidation for unsaturated alloys.
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Acknowledgements
Major advisor: Dr. John E. Morral
Dr. Ronald N. Caron at Olin Corporation
Dr. Carelyn E. Campbell at NIST
Dr. Caian Qiu at Ques Tek
UConn staff: Mary Anton, Fred Massicotte
All members of UConn diffusion group
National Science Foundation
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Applications
Design alloys with improved oxidation resistant
Design intermetallic alloys capable of protective scale formation ( e. g. Al2O3, Cr2O3 and SiO2)*
Synthesize functional ceramic surface structures (e.g. nitride and carbide catalysts Co3Mo3N or Co3Mo3C) by gas-metal reactions (oxidation, nitridation, carburization, etc.)*
* M. P. Brady and P.F. Tortorelli, Intermetallics, 12(2004) 779-789
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Approach: Experimental studies
Rhines Pack: Cu (shot) + Cu2O (powder) in a stainless steel tube
Sample size : 10×10 ×20 (mm)
The tube was welded at the ends in argon atmosphere
Cu-Ni alloy
Cu2O powder
Cu shot
Stainless steel tube
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Experimental results: Optical microstructures
---- Cu atom --- Cu+1 --- O-2
Cu shot +Cu2O powder
Stainless steel tube
Cu-Ni alloy
(1) The mixture of Cu and Cu2O in a Rhines Pack
Two Cu sources for the new Cu layer:
Ni : 6.59 cm3/mole NiO: 11.15 cm3/mole
(2) Internally oxidized Cu-Ni alloys
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Experimental results: EDX
Concentration profiles of Cu-10% Ni alloys oxidized at 950° C
Estimated position of oxidation frontier
0 50 100 150 200 2500
2
4
6
8
10
12
14
16N
i %
Distance from surface (micron)
Ni% in matrix Average Ni%
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Experimental results: EDX
New Cu layer at the surface:
4000
4500
Quantitative results:
Cu --- 99.69 wt%Ni --- 0.31 wt%
Kα1 Kβ1 Lα1 Lβ1
Cu 8.046 8.904 0.93
0.851
0.95
Ni 7.477 8.263 0.863
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Experimental results: Phase identification (XRD)
XRD patterns of Cu-20%Ni – before oxidation
0
500
1000
1500
2000
2500
3000
3500
10 20 30 40 50 60 70 80 90 100 110
2 theta
Inte
nsity
(1 1 1)
(2 2 0)
(2 0 0)
(3 1 1)(2 2 2)
Cu-20%Ni
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Experimental results: Phase identification (XRD)
XRD patterns of Cu-20%Ni – after oxidation
0
1000
2000
3000
4000
5000
10 30 50 70 90 1102 theta
Inte
nsity
(1 0 1) (1 0 4)
(0 1 2)
(1 1 3)(0 2 4)(2 0 2)
NiO
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Experimental results: Phase identification (XRD)
NiO crystal structure:
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Experimental results: EDX
Concentration profiles of Cu-Ni alloys oxidized at 950° C for 3 hours
-50 0 50 100 150 200 250 300 350 4000
4
8
12
16
20
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Ni%
in m
atrix
Distance from surface (micron)
20 wt% Ni 10 wt% Ni 5 wt% Ni
Estimated position of oxidation frontier
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Background: Existing models of internal oxidation
(a)
(b)
(c)
(a) C. Wagner, Z. Electrochem, 63 (1959) 772. (b) J. A. Nesbitt, Oxidation of Metals, 44 (1995) 309. (c) G. Bohm et al. Acta Metall.,12 (1964) 641
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Background: Venn diagram
A:Zero solubility
productK=0
B: DB = 0
D:Non-Local equilibrium
The classic mode = )()( BADA ∩∪∩
CDLocal equilibrium model =
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Background: Local equilibrium assumptions
The compositions and amount of
each phase are given by the local
average composition, the phase
diagram, and the lever rule.
Nucleation and growth rate of
precipitates are so rapid that only
long range diffusion need be
considered.
βCC
αCC
αBC β
BC
α
β
A B
C
CC
BC
α+β
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Simulation results: EFM
Diffusion paths:
0.00
0.05
0.10
0.15
0.20
0.25
0.30
9.6 9.7 9.8 9.9 10.0 10.1
Diffusion path in alpha
Diffusion path in alpha+oxidealpha/alpha+oxide phase boundary
tie line
CO
CB
α
α + oxide
Simulation conditions: , , , ==−=5106.9 −×=K
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Simulation results: DICTRA
Diffusion path:
α + oxide
α
Simulation conditions: , , , ==−=5106.9 −×=K
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DICTRA simulation
An ideal A-B-O solid solution system
Three elements: A - solventB - soluteO - fast diffuser (DO>>DB)
Two phases:matrix phaseline compound (BO)
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Simulation results: DICTRA
Effect of on oxide mole fraction:0BC
Distance x ( m)410−×
f oxi
de
0.00
0.10
0.20
0.30
0.40
0.50
0.0 1.0 2.0 3.0 4.0 5.0
%100 =BC
%150 =BC
%200 =BC
Simulation conditions: , , =−=5106.9 −×=K
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Simulation results
Comparison of EFM and DICTRAEFM DICTRA
Application Unsaturated case Saturated case
Boundary conditions
= Constant = Constant
[Deff] Constant Concentration dependent
Phase boundary Linear
β β →1 0.03 < β < 0.55
Local equilibrium conditions Satisfied Satisfied
KCC OB =
SOC
0=BJx
CDJ BBB ∂∂
−=
SOC
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Interesting diffusion paths
two-phase region
Zigzag shapeSingle-phase region
Serpentine shape
C1→
C2→
α
βα + β
C2→
C1→
⎥⎦
⎤⎢⎣
⎡
2221
1211
DDDD
Major eigen vector direction
Gibbs Phase law: f = c – p + 2