Grain Boundary Oxidation Processes and High Temperature … · 2018-03-19 · 12th Annual...
Transcript of Grain Boundary Oxidation Processes and High Temperature … · 2018-03-19 · 12th Annual...
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12th Annual GTT-Technologies Workshop
17th June, 2010
M. Auinger and M. Rohwerder
Grain Boundary Oxidation Processes and High Temperature Corrosion
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Overview
• Theoretical Background
• Programme Description (Linking ChemApp with COMSOL)
• Comparison with Experimental Results
• Introducing Chemical Potentials
• Summary
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Oxidation Processes
Figure: Schematic process of grain boundary oxidation in steel sheets, fabricatedby the hot-rolling technique.
scale (mainly ‘FeO’)
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Oxygen Partial Pressure
Figure: Thermodynamic stability diagram of iron and iron oxides with respect totemperature and oxygen partial pressure according to SGTE Pure Substance Data.
0 250 500 750 1000 1250-100
-75
-50
-25
0
γ-Fe
oxyg
en p
ress
ure
log(
p(O
2)/po)
temperature θ / °C
α-Fe
Fe3O4
Fe2O3 (hematite)
'FeO' (wustite)
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Programme Algorithm
0.00 0.25 0.50 0.75 1.00-40
-35
-30
-25
-20
-15
-10Fe2O3 (hematite) + Al2O3
Fe3O4 + FeAl2O4
oxyg
en p
ress
ure
log(
p(O
2) / p
o)
mole fraction aluminium xAl
Fe + Al
Fe + Al2O3
'FeO' + FeAl2O4
Fe + FeAl2O
4
Fe3O4 + Al2O3
Al2O3 + FeAl2O4
700 °C
element migration(COMSOL Multiphysics)
chemical reaction(ChemApp)
( )( ) ( )( )tx,iTx,i
tx,i c.D=dt
dc∇div
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Data HandlingAl - total
Al
Al-Oxide
Figure: Spatial phase distributions of Fe, 2 wt-% Al (4.05 mol-% Al) after oxidationat p(O2) = 10-22 bar for 60 min at 700 °C.
Al
Al2O3
FeAl2O4
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Calculation of Oxidationdepth - Distribution
0 25 50 750.000
0.025
0.050
0.075
0.100
rela
tive
abun
danc
e
depth x / µm
µ, σ
0 25 50 75 1000.00
0.25
0.50
0.75
1.00
Data: Data1_CModel: SLogistic1Equation: y = a/(1 + exp(-k*(x-xc)))Weighting: y No weighting Chi^2/DoF = 0.00721R^2 = 0.99588 a 3.20455 ±0.00818xc 29.5835 ±0.10386k 0.22165 ±0.00442
Frac
tion
of m
etal
lic C
hrom
ium
depth x / µm
Oxides metallic Cr
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Dependencies with Grain Size
Figure: Grain size dependency of the spatial distribution of chromium oxides in Fe, 3 wt-% Cr after finished cooling procedure (dGB = 500 nm).
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Comparison with the Experiments
Figure: Simulation of spatial phase distributions of Fe, 1 wt-% Si (1.97 mol-% Si) after oxidation at p(O2) = 10-22 bar for 90 min at 650 °C (left). AES-captions (right).
AES pictures by S. Borodin, MPIE
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Ternary Alloy Systems
Figure: Thermodynamic stability (according to SGTE Pure Substance Data) of silicon and aluminium containing oxide phases in an iron alloy at 650 °C.
0.00 0.25 0.50 0.75 1.00-35
-30
-25
-20Fe3O4 + FeAl2O4 + SiO2FeO
Fe + FeAl2O4 + Fe2SiO4
Fe + SiO2 + FeAl2O4FeAl2O4
Fe + Al2O3 + SiAl2O5
SiAl2O5
Fe + SiO2 + SiAl2O5
Fe + Al2O3 + FeSi
Oxy
gen
Parti
al P
ress
ure
log(
p(O
2)/p0)
xSi/(xSi+xAl)
3 w
t-% S
i, 1
wt-%
Al
Fe + Al + FeSi
Atmosphere
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Ternary Alloy Systems
Figure: Spatial phase distributions of silicon, aluminium and their oxides in Fe, 3 wt-% Si, 1 wt-% Al after oxidation at p(O2) = 10-22 bar for 110 min at 650 °C.
Si SiO2 Fe2SiO4 SiAl2O5 FeAl2O4 Al2O3 Al
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Programme Benchmark
Figure: Spatial phase distributions in a real alloy after oxidation at p(O2) = 10-22 bar in a technical cooling programme.
Fe FeO Fe3O4 Fe2O3 Fe2MnO4 FeCr2O4 FeSiO3 SiFe2O4 FeAl2O4 Fe3C
Mn MnO MnOx Fe2MnO4 SiMn2O4 SiMnO3 MnAl2O4 Mn23C6 Mn7C3
Cr Cr2O3 FeCr2O4 Cr23C6 Cr7C3 Cr3C2
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Programme Benchmark
Figure: Spatial phase distributions in a real alloy after oxidation at p(O2) = 10-22 bar in a technical cooling programme.
Si SiO2 FeSiO3 SiFe2O4 SiMn2O4 SiMnO3 SiAl2O5 SiC
Al Al2O3 FeAl2O4 MnAl2O4 SiAl2O5 AlPO4
C Fe3C Mn23C6 Mn7C3 Cr23C6 Cr7C3 Cr3C2 SiC
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Programme Benchmark
Figure: Spatial phase distributions in a real alloy after oxidation at p(O2) = 10-22 bar in a technical cooling programme.
C P2O5 AlPO4
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Part II
Introducing chemical Potentials
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Thermodynamics in normal life
http://adsjapan.blogspot.com (dl 10.06.2010)
Figure: Shibuya (渋谷) crossing in Tokyo at night when pedestrian lights are green.
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Thermodynamics in normal life
http://www.gettyimages.com (dl 10.06.2010)
Figure: Shibuya crossing in Tokyo in the evening when pedestrian lights are red.
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Some Formulas
general description
single phasecDJ A ∇−=
μ∇−= LJ A
∑∑ Δ+Δ+Δ−Δ=Δ nzFnTSpVG ϕμ
( )aRTo ln+= μμ
L=
( )cRTo γμ ln+=
⎟⎟⎠
⎞⎜⎜⎝
⎛∇+∇−∇−= γ
γμ RTLc
cRTL oc
cLLJ A ∇∂∂
−=∇−=μμ
( )cRTo ln~ += μ
321D
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Simulation Results
[1] Blavette et al. Microsc. Microanal. 13 (2007) 464
Figure: Numerical simulation of segregation (left) and 3D atom probe tomography of segregated boron atoms along the grain boundary in a NiAl superalloy [1] (right).
t = 0
t ∞concentration
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Summary
• simulations of (oxide) phase distributions in local thermodynamic equilibrium with ChemApp
• good agreement within experimental error for binary alloys
• some deviations for ternary systems
• concentration gradients alone can not explain interphase transport phenomena
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Again in real life…
Figure: Castle Schönbrunn (Vienna, Austria) in the summer time.
www.wikipedia.com (dl 10.06.2010)
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Acknowledgements
Funding
Christian Doppler Forschungs-gesellschaft
voestalpine Stahl GmbH
Academic partners
Institute of Chemical Technologies and Analytics