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Review: chemical compatibility of SiC/SiC
composites with the GFR environment
C. Cabet
Laboratoire of Non Aqueous Corrosion, CEA Saclay, FRANCE
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Aqueuse
1
01.04.15
GFR and SiC/SiC composites
Fuel assembly
850°C
Heat
eXchanger
Helium
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Introduction
2
Concepts of fuel assembly
Needle concept
composite
SiC-SiCfibers
Fission gas
Actinide
compound :
UPuC or UPuN
(56%vol of fuel)
diffusion barrier
refractory metal : We, Mo, Cr,…
Plate
concept
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Introduction
3
Requirements on material for fuel assembly
• Containment of fuel and FP
• Refractory behaviour
– Resistance to normal operating temperatures (about 900°-1200°C)
on extended lifetimes
– Confining of FP during a transient incident up to 1600°C
– Mechanical integrity after a major accident up to 2000°C
• High thermal conductivity (>10 W/m.K)
• Transparency to fast neutrons
• Mechanical strength and creep resistance
• Ability to dissolve in nitric acid
• Workability and assemblage
• Resistance to corrosion/ oxidation
Best candidate material : SiCf/SiCm
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Introduction
4
GFR environment
• High temperature: 900-1200°C
+ short term transitory up to 1600°C (confining) and accident
up to 2000°C (integrity)
• Long in-core times
• No inspection, no repair
• Cooling gas : impure helium
secondary circuit
cooler
H2 ?
Helium
+ traces
air, H2O
Helium
air, H2O
refueling
maintenance
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
air, H2O,
CO, CH4 ?
degassing
Introduction
5
SiCf/SiCm usual applications
Turbines
Rocket
engines
•
•
•
•
High temperature
Oxidative atmospheres
Inspection and repair
Short term
Aircraft
engines
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Introduction
6
SiCf/SiCm compatibility with GFR physicochemical conditions over long term ?
• Thermal stability
Lifetime
prediction
• Oxidation resistance
• Consequences of thermal aging and oxidation
on the mechanical (and confining) properties
• Improvement strategies
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Introduction
7
Content
• Introduction on the GFR application
• SiCf/SiCm structure and fabrication
• Thermal stability
• Oxidation propertis
• Composite resistance
• R&D needs to qualify SiC/SiC for GFR applications
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
8
SiCf/SiCm structure
SiC-based
matrix
SiC-based
fibre ~10µm
crack
interphase (C) ~0.1µm
Fibres in bundle
UD or 1D
2D
3D
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
SiCf/SiCm structure and fabrication
9
SiC based matrix (SiC + Si)
• CVI Chemical Vapor Impregnation
porosity
• PIP Polymer Impregnation and Porolysis
preceramic
pyrolysi
s
Carbon coated
fibre tows
Pre-forming
Polymer
infiltration
Pyrolysis
• RMI Reative Melt Infiltration
• SI-HPS Slurry Infiltration
and High Pressure Sintering
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
additives
10
SiC-based fibres: fabrication
spinning
curing
Weak fibres
Dense fibres
PCS
• 1st generation
– cure in oxygen at T~1200°C
– Si-C-O: 2nm SiC + C + SiCxOy
• 2nd generation
– cure by electron beam in inert atm at T~1400°C
– Si-C + C (+ 0.5% O)
• 3rd generation or nearly stoichoimetric
– cure at 1800°-2000°C + optimization
– thin C layer on the surface
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
SiCf/SiCm structure and fabrication
11
SiC-based fibres: 3 generations
• Exemple of the development of the Nicalon fibres by Nipon Carbon
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
12
Interphase
• Compliant material
• Thin layer ~100nm
• « leaf » structure
– pyrocarbon
– hex-BN
– Multilayer
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
13
Content
• Introduction on the GFR application
• SiCf/SiCm structure and fabrication
• Thermal stability
– Monolithic SiC
– Matrix
– Fibres
• Oxidation properties
• Composite resistance
• R&D needs to qualify SiC/SiC for GFR applications
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
14
SiC phase diagram
• Stoichoimetric
• no other intermediate
compound
• SiC
2540°C
(SiC)(l) + C
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
15
Thermal stablity of SiC
in vacuum or inert atmopshere
• Thermodynamic calculation
SiC
C + Si(g)
+ recrystalisation
SiC + Si
104/T (K)
• Kinetic factors: SiC stable up to ~1600°C
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
16
Thermal Stability of the matrix
in vacuum or inert atmopsheres
• SiC and SiC/C matrixes are stable up to about 1600°C
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
17
Thermal Stability of fibres
Fibres of the 1st generation: Si-C-O
• Basically instable à T>1200°C
• (SiC, C, SiC2xO1-x)  w SiC + x C + y CO(g) + z SiO(g)
Porous C/SiC
(large grains)
1300°C
Mass loss
Decrease the
creep strength
1200°C
Creep curves for Nicalon fibres tested
in pure Ar under 0.7 GPa
Mass loss for Nicalon fibres tested in
pure Ar
[Bodet et al. J Amer Ceram Soc 79 (1996) 2673]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
18
Thermal Stability of fibres
Fibres of the 2nd generation: Si-C(0.5% O)
• Stable up to 1350°C
• (SiC, C) + Otrace(g,s)  SiC + CO(g) +C
Large grains Mass loss
= r
Si-C-O Nicalon NL202 and Si-C Hi-Nicalon
Tensile
strength
at
(as-received
and and
heatYoung’s
treated)modulus
fibres under
RT
of Si-C
Hi-Nicalon
after
annealing
under
100kPa
Ar (heating
rate:
10°C/min)
[Chollon
100kPa
Ar forSci
tp=1hrs
exept333]
*tp=10hrs)
et al., J Mater
32 (1997)
[Chollon et al., J Mater Sci 32 (1997) 333]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
19
Thermal Stability of fibres
Nearly stoichiometric fibres
• Stable up to very high temperatures 1800°-2000°C
• Some SiC grain growth
• Good mechanical properties up to 1400°-1500°C
Strengh as a function of
temperature for 3rd gen fibres with
a 250mm gauge length
[Bunsell and Piant, J Mater Sci 41
(2006) 835]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Thermal stability
20
Content
• Introduction on the GFR application
• SiCf/SiCm structure and fabrication
• Thermal stability
• Oxidation properties
– Monolithic SiC
• passive oxidation
• active oxidation
– Matrix
– Fibres
– Interphase
• Composite resistance
• R&D needs to qualify SiC/SiC for GFR applications
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
21
Oxidation of SiC at high Po2: passive oxidation
• Same mechanism that the oxidation of Si and other ceramics
– SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g)
– SiC(s) + 2 O2(g) = SiO2(s) + CO2(g)
Very
protective
T>800°C
Monolithic SiC
– Linear-parabolic kinetics
KP
x
Parabolic rate
constant
2

KL
 (t   )
x
Scale
thickness
linear rate
constant
a-SiC in 1 atm air
[Costello & Tressler, J Am Ceram Soc 64 (1981) 327]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
22
Oxidation of SiC at high Po2: mechanism
  Ea 
K p  B . exp 

 RT 
T>800°C
Monolithic SiC
Growth rate = oxygen transport through the SiO2 scale
T>1400°C
Ea 150-300 kJ/mole
atomic diffusion
cristobalite
T<1400°C
Ea 300 kJ/mole
molecular diffusion
amorphous SiO2
90µm
MEB image of sintered a-SiC 6hrs at
1400°C in 1 atm air
[Costello & Tressler, J Am Ceram Soc 64
(1981) 327]
KP for the oxidation of single-crystal SiC
under 0.001 atm O2
[Zheng, J Electrochem Soc 137 (1990) 854]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
23
Oxidation at high Po2: polycrystalline SiC
  Ea 
K p  B . exp 

 RT 
• Determining factors for Kp
– Polytype
– Porosity (fabrication
process)
– Additives and impurities
• Formation of a silicate
with a lower viscosity
( transport of O )
• Modify the
crystallisation
HP SiC with different %Al2O3 at 1370°C in 1 atm O2
[Opila
Jacobson,for
in Materials
and technology
Kp from
the& literature
different science
type of SiC
Vol.et
19,
RW.
Cahn
et al.Soc
Ed.72
(2000)]
[Narushima
al.,
J Am
Ceram
(1989) 1386]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
24
Oxidation at high Po2: effect of water vapour
• Passive oxidation by water vapour
T<1400°C
SiC + 2 H2O(g)
SiO2 + CH4(g)
T>1400°C
SiC + 3 H2O(g)
SiO2 + CO2(g) + 3 H2(g)
Some water
vapour
the oxidation
• Higher
oxidation
rateincreases
in pure water
vapour rate
SiO2(s) + H2O(g) = SiO(OH)2(g)
SiO2(s) + 2 H2O(g) = Si(OH)4(g)
CVD-SiC at 1200°C in pure CO2,
pure O2 and 50%H2O/50%O2
[Opila & Nguyen., J Am Ceram
Soc 81 (1998) 1949]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
25
Oxidation of SiC at low Po2: active oxidation
• Same mechanism that the oxidation of Si and other ceramics
– SiC + O2(g) = SiO (g) + CO(g)
Mass Change
Volatilization
ka
CVD-SiC in 0.1 MPa at 1600°C – Po2 in Ar
Corresponding rate constant for
from 0 to 160Pa
active oxidation at two gas flow rates
[Goto et al., Corrosion in advanced ceramics, KG Nickel Ed. (1993) 165]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
26
Oxidation of SiC at low Po2: active oxidation
• Transition point between active and passive oxidation
• Determining factors for transition
– Temperature
– Po2
– SiC purity
– Vgas
– Total pressure
Active to passive transitions from the
literature for different types of SiC
[Opila & Jacobson, in Materials science and
technology Vol. 19, RW. Cahn et al. Ed. (2000)]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
27
Oxidation at low Po2: effect of water vapour
• Active oxidation by water vapour
SiC + 2 H2O(g) = SiO(g) + CO(g) + 2 H2(g)
Corrosion rate
active
Active to passive
transition
Flexural strength at RT
passive
1400°C
PLS α-SiC at 1300° and 1400°C 10min in H2 with different P(H2O)
[Opila & Nguyen., J Am Ceram Soc 81 (1998) 1949]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - SiC
28
Oxidation of SiC-based matrixes at high Po2
• Under oxidizing atmosphere CVD-SiC (representative of CVI-SiC:
Passive oxidation
Thickness of the SiO2 scale
Crystallisation
Amorphous SiO2
CVD-SiC representative of CVI-SiC at 1000°C and 100 kPa
[Naslain et al. J Mater Sci 39 (2004) 7303]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - matrix
29
Oxidation of fibres: passive mode at high Po2
• Growth of silica around
the fibre surface
SiO2
(2nd and 3rd generation fibres)
Flexural strength
Mass change at 1300°C
Mass change in Ar-25%O2
Hi-Nicalon S
Hi-Nicalon
Nicalon
Hi-Nicalon fibres (SiC-C) in Ar-O2 at 1300°C
[Shimoo et al. J Mater Sci 35 (2000) 3301)]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation in Ar-O2 at 1500°C
[Shimoo et al., J Ceram Soc Japan 108
(2000) 1096)]
Hi-Nicalon fibres (SiC-C) in Ar-25%O2
Oxidation - fibres
30
Oxidation of fibres: active mode at low Po2
• Volatilization of SiO(g)
SiC(s) + O2(g) = SiO(g) + CO(g)
+ recrystallisation of SiC
RT tensile strength
SiO2
Mass change at 1500°C
Passive
oxidation
Active
oxidation
Lox M fibres in Ar-O2 at 1500°C
[Shimoo et al. J Mater Sci 37 (2002) 4361)]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
RT tensile strength for fibres heated for
SiC
20hrs in Ar-O2 at 1500°C
Oxidation - fibres
31
Oxidation of fibres: case of 1st generation
Mass change
• Passive oxidation with SiO2 growth
SiC + 3/2O2(g) = SiO2 + CO(g)
No thermal decomposition of Si-C-O
• Thermal decomposition of Si-C-O
SiCO = SiO(g) + CO(g) + SiC + C
+ recrystallisation of SiC
• Active oxidation
SiC + O2(g) = SiO(g) + CO(g)
+ recrystallisation of SiC
Nicalon CG fibres in Ar-O2 at 1500°C
[Shimoo et al. J Amer Ceram Soc 83 (2000) 3049]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - fibres
32
Oxidation of fibres: active to passive transition
• As for pure SiC, there is an active to passive transition
Mass change
Fibres heated 72 ks in Ar-O2 at 1500°C
[Shimoo et al. J Mater Sci 37 (2002) 1793]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Active to passive transition
Po2 for active to passive transition
Oxidation - fibres
33
Oxidation of fibres: effect of water vapor at high Po2
Ln (Kp) (h-1)
• As for pure SiC, H2O increases the oxidation rate
Kp for Hi-Nicalon fibres tested in N2/O2/
H2O under 100 kPa and Po2=20 kPa
[Naslain et al. J Mater Sci 39 (2004) 7303]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Tensile strength of SiC fibres after 10h
at 1400°C in dry or wet (2%H2O) air
[Takeda et al. J Nucl Mater 258-263
(1998)1594]
Oxidation - fibres
34
Oxidation of the interphase at any Po2
• Carbon is highly oxidizable at T>600°C
– C + O2(g) = CO2(g)
– C + ½ O2(g) = CO(g)
– C + 2 H2O(g) = CO2(g) + 2 H2(g)
– C + H2O(g) = CO(g) + H2(g)
• Oxidation rate is dertermined by
– Temperature
– Po2
– Total pressure
– Gas flow rate
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Oxidation - interphase
35
Content
• Introduction on the GFR application
• SiCf/SiCm structure and fabrication
• Thermal stability
• Oxidation properties
• Composite resistance
– Thermal aging
– Oxidation
– Improvement of the HT oxidation resistance
• R&D needs to qualify SiC/SiC for GFR applications
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
36
Thermal aging of UD SiCf/SiC (inert gas)
•
•
•
•
UD-SiCf/C/PIP-SiCm
Nicalon CG - 1st generation SiCO : thermal decomposition
Hi-Nicalon - 2nd generation SiC-C (0.5% O) : stable up to 1350°C
Hi-Nicalon S - 3rd generation: nearly stoichiometric
Mass change
Residual oxygen
Fracture strength
UD SiCf/C/PIP-SiCm 3.6ks in vacuum [Araki et al. J Nucl mater 258-263 (1998) 1540]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – thermal aging
37
Thermal aging of 2D SiCf/SiC (inert gas)
• 2D Nicalon CG/C/CVI-SiC
• 1st generation SiCO : thermal decomposition
SiCO = SiO(g) + CO(g) + SiC + C
• Interaction with the interphase
Tensile strength
SiO(g) + 2 C = SiC + CO(g)
coarse SiC
Interfacial decohesion (weakening
of the fibre-matrix bounding)
Partial consumption of the interphase
with formation of coarse surface SiCgrains (weakening of the fibres)
Total consumption of the interphase
with decomposition/crystallisation
(fully brittle)
Stress-strain curves of 2D Nicalon/C/SiC composite at RT
after thermal aging in vacuum under various conditions
[Labrugère et al. J Eur Ceram Soc 17 (1997) 623]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – thermal aging
38
Passive oxidation of model SiCf/SiCm (high Po2)
• Passive oxidation of fibres and matrix
– SiC + 3/2 O2(g) = SiO2 + CO(g)
– SiC + 2 O2(g) = SiO2 + CO2(g)
• Oxidation of the interphase
– C + O2(g) = CO2(g)
– C + ½ O2(g) = CO(g)
[Filipuzzi et al. J Amer Ceram Soc 77 (1994) 459]
• Model UD Nicalon/C/CVI-SiC no coating on the back and front surfaces
–  gas phase diffusion of O2 and CO in the pore
–  reaction of O2 with the C interphase
–  diffusion of O2 in SiO2 and reaction with SiCf
– diffusion of O2 in SiO2 and reaction with Sim
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
39
Passive oxidation of 2D SiCf/C/SiCm (high Po2)
• Oxidation of the interphase
• Sealing
– C +of
O2the
(g) pore
= CO2(g)
• Passive
the matrix
– C + oxidation
½ O2(g) = of
CO(g)
– SiCoxidation
+ 3/2 O2(g)
SiO2 and
+ CO(g)
• Passive
of =fibres
matrix
SiC ++ 3/2
2 OO
= SiO2 +
CO2(g)
–– SiC
2(g)
2(g) = SiO
2 + CO(g)
– SiC + 2 O2(g) = SiO2 + CO2(g)
Mass change
Residual Young’s modulus
2D Nicalon / C (δ=0.1 µm)/ CVI-SiC without an anti-oxidation coating heated for 35hrs
in air at different temparatures [Huger et al. J Amer Ceram Soc 77 (1994) 2554]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
40
Active oxidation of 2D SiCf/C/SiCm (low Po2)
• SiC-based fibers are basically instable
SiC + O2(g) = SiO(g) + CO(g) + recrystallisation of SiC
• Strong impact on the fibre strength that provides the mechanical
properties of the composite
– Surface flaws  cracks
Fully brittle
no test
RT tensile strength of fibres heated for
3.6ks in Ar-O2 at 1500°C
[Shimoo et al. J Mater Sci 37 (2002) 4361)]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
41
Oxidation of composites under load
• Even for coated specimens
• At >0-100MPa  matrix cracking
• At 500-1000°C
• Jones et al. proposed a Po2/T map
SiO2 on the fibres
Interphase removal
Fibre creep only
[Jones et al. J Amer Ceram Soc 83 (2000) 1999]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
Crack velocity for model composite with
Nicalon fibres at 1100°C
[Jones et al. Mater Sci Eng A198 (1995) 103]
composite – oxidation
42
Improvement of the oxidation resistance: EBC
• Environmental Barrier Coating
SiO2
SiC
CVD SiC
B-based phase
Si or SiC bound coat
r (MPa)
• Boron forms an oxide with a low melting
point [Tf(B2O3)=450°C]
2B + O2  B2O3
RT2BN
flexural
2D+ Ostrength
2  B2Oof
3 +aN
2(g)
Nicalon/C/CVI-SiC with and without
B4C + 4 O2  2 B2O3 + CO2(g)
a CVD-SiC
seal coat after oxidation
SiB
+
11/2
in air at
6 1000°CO2  3 B2O3 - SiO2
[Lowden,
in boron
Designing
Ceramic
• Fusible
oxide
or boron silicate seal
Interfaces
II, Peteves
Ed. crack
(1993) tips
157]
the porosity
and the
Time at 1000°C in air (h)
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
43
Improvement of the oxidation resistance:
self-healing matrixes
• Matrix with dispersed particles
Applied stress
– Boron-based particles: B4C, BN, SiB6
– Forms a healing oxide
– Matrix fabricated by PIP
• Multilayer matrix
– Low
melting
Nicalon
fibresphase X: B, B4C, Si-B-C
– Compliant material Y: PyC, C(B), hex-BN
– Matrix fabricated by P-CVI: (X-Y-X-Y’)n
2D-Nicalon/C/
SiC+C-B
2D-Nicalon/C/SiC
Fatigue life (tensile) at 900°C in air
[Steyer et al., J Amer Ceram Soc 81
(1998) 2140]
[Lamouroux et al., Composites
Sci Technol 59(199) 1073]
Time (h)
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
44
Improvement of the oxidation resistance:
alternative interphases
• B-based interphases: hex-BN or C(B)
2BN + O2  B2O3 + N2(g)
2B + O2  B2O3
Forms a healing oxide
• Multilayer interphase
– Oxidation resistant material: SiC, TiC
– Compliant material Y: PyC, hex-BN
– Deposition by P-CVI: (X-Y-X-Y’)n
Fatigue life (4-point bending)
of 2D-Nicalon/PyC or BN/CVISiC in air at 600° and 950°C
[Lin et al., Mater Sci Eng A321
(1997) 143)]
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
composite – oxidation
45
Content
• Introduction on the GFR application
• SiCf/SiCm structure and fabrication
• Thermal stability
• Oxidation
• Composite resistance
• R&D needs to qualify SiC/SiC for GFR applications
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
46
R&D needs for qualifing SiC/SiC composite for GFR
Corpus of data on the thermal aging and
oxidation behaviour of composites
• All studies are on a very short term!
• For monolithic SiC: wide ranges of
temperature and P(O2) were covered
– Widespread results (strong dependence
to SiC purity and nature)
– Few data on the effect of water in
relevant ranges
• For components: some domains of
temperature and P(O2) were investigated
– Strong influence of chemistry, structure
and fabrication processes
 Pre-selection of candidate technologies
and systematic study
• For whole composites: some particular
studies at high P(O2)
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
conclusion
Helium +O2, H2O
900°-1200°C
Very long times
+
Short time at 1600°C
(even 2000°C)
47
R&D needs for qualifing SiC/SiC composite for GFR
Choice of best state
of the art materials
Helium +O2, H2O
Control of the
environment
• Stoichiometric fibres
• Control of the Po2 (lower
and upper limit)
• Low-porosity matrix
(+dispersed particles) or
multilayer matrix
• Control of the PH2O
(upper limit)
• Environmental Barrier
Coating
• Multilayer interphase
900°-1200°C
Very long times
• Limit on the temperature
• Design
Acceptability of
additives and B ?
DEN/DANS/DPC/SCCME
Laboratoire d’Etude de la Corrosion Non Aqueuse
conclusion
48
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