Self-Healing EBC Scales on SiC James L. Smialek, QuynhGiao N. Nguyen, R. Craig Robinson
description
Transcript of Self-Healing EBC Scales on SiC James L. Smialek, QuynhGiao N. Nguyen, R. Craig Robinson
Glenn Research Center Materials Division
Protective SiO2 scales react in hot gas environment, form volatile Si(OH)4, give paralinear (recession) kinetics.
kl gas transport model, Opila, et al:
Self-Healing EBC Scales on SiCJames L. Smialek, QuynhGiao N. Nguyen, R. Craig Robinson
422
222
)(22
OHSiOHSiOCOSiOOSiC
)/()/108exp(0.2)( 22121
22 hrcmmgv
PPRTkJHPBRk
Total
OHl
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Linear Weight Loss of SiC in HPBR6 atm, 20 m/s
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10,000/T (K)5.8 6.0 6.2 6.4 6.6 6.8
k l/(P
1.50 )(v
0.50 )
10-4
10-3(6)
(15) (5)(10)
1400 C 1200 C1300 C
kl=2.06(e-108kJ /mol*RT)(P1.50)(v0.50)
Atm.=
Normalized Recession Rate5-15 atm, 10-30 m/s
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Present Solution: Plasma sprayed EBC oxides 4. BSAS topcoat (barium strontium alumino-silicate)-----------------------------------------------------------------------------3. Mullite + BSAS intermediate layer (furnace sprayed)-----------------------------------------------------------------------------2. Si bondcoat-----------------------------------------------------------------------------1. Molten salt etched, washed, and dried CMC surface
Alternate approach: EBC scales formed on additives
TiC (TixSiy,TiAl, TiCrAl) TiO2, Al2O3
Hot pressed SiC-%TiX compositesFurnace (air, 50% H2O), HPBRCharacterization, optimization, kinetic models
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SiO2
SiC
Ti-X precursors:TiC, TixSiy, TiAl
Idealized EBC Scale Schematic
critical kp 2m2/hr for healing (100hr @ 10v/o, 10 m radius)
Self-healing scalesTiO2 (Al2O3) kp= 105 (102) SiO2 kp
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Pertinent Oxidation Background(non-oxide, multiphase ceramics)
• Si3N4–TiN, TiC,… Gogotsi, Lavrenko, Yaroshenko…
Bellosi, Vincenzini, Tampieri…Buljan, Zilberstein…
• ZrC, HfC (-TiC), Shimada,....
– At 25 wt.% TiN, continuous TiO2 surface scale forms.
– TiO2 nodules are only over individual particle at lower loadings.
– HfTiO4 inner scales develop under TiO2 surface scale.– Carbon found in scale at carbide interface (titanium oxycarbide?).
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Short Subjects
• 50-50 SiC-TiC furnace data vs T• 50-50 SiC-TiC, 1330oC HPBR oxidation, scale microstructure• 50-50, 90-10, 1000oC HPBR weight change• 50-50 SiC-TiC, 1000oC HPBR microstructure• TiSi2 furnace oxidation
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Self-Healed TiO2 Scale Formed on SiC-50TiC
As-polished SiC-TiC After 500 hr oxidation at 1000oC
25x
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Furnace Oxidation of SiC-50TiC Composites at 1000-1300oC
oxidation time, hours0 20 40 60 80 100 120
spec
ific
wei
ght c
hang
e, m
g/cm
2
0
10
20
30
40
50
60
goal
1000o
1100o
1200o
1300o
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Furnace Oxidation of SiC-50TiC Composites at 1000-1300oC
time1/2, hr1/2
0 2 4 6 8 10
spec
ific
wei
ght c
hang
e, m
g/cm
2
0
10
20
30
40
50
60
goal
1000o
1100o
1200o
1300o
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Arrhenius Plot of SiC-50TiC Oxidation Rates
1/T, 104 K-16 7 8pa
rabo
lic o
xida
tion
rate
, kp,
mg2 /c
m4 hr
0.01
0.1
1
10
goal
1100o
1200o
1300o
1000o170 kJ/moleoK
200 kJ/moleoK oxidation of Ti195 kJ/moleoK oxidation of TiN220 kJ/moleoK oxygen diffusion in Ti189 kJ/moleoK oxygen diffusion in TiO2
455 kJ/moleoK oxidation of Si3N4-Al2O3-TiN
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CSi
Ti
C
SiCDark phase
TiCLight phase
Unaffected coreSiC-50TiC, HPBR,1330oC, 7.5 hr
(dispersed porosity)
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6kV SiC spectra
C
Si
C
Si
C
Si
CSi
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3
C
TiO
6kV TiC spectrum
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C
Ti, O
100 m
TiO2 External Scale Formed in HPBR SiC-50TiC, 1330oC, 7.5 hr
Surface facets Cross section
20 m
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C
TiO
C
Ti, O
Si
Ti, k
6kV TiO2 spectra
15kV
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1
2 10 m
C
Ti, O O1) TiO2
Si2) SiO2
immediate subscale
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HPBR Oxidation of SiC-TiC Composites at 1000oC
oxidation time, hours0 20 40 60 80 100 120
spec
ific
wei
ght c
hang
e, m
g/cm
2
0
10
20
30
40
goal
50-50furnace90-10
50-50
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SiC-50TiC, HPBR, 1000oC, 60 hr
10 m
10 m
SiO2in TiO2
SiC in SiO2
10 m
10 m
100 m
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Furnace Oxidation of TiSi2 Composites at 1000-1300oC
oxidation time, hours0 20 40 60 80 100 120
spec
ific
wei
ght c
hang
e, m
g/cm
2
0
1
2
3
1000oC1100oC1200oC1300oCgoal
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Preliminary Status Report
• Hot pressed SiC-TiC; oxidized at 1000-1300oC.• At 25 and 50%, distinct, oversealing TiO2 scales formed.• Oxidation rates greatly exceeded target; porosity. • HPBR tests indicate even higher growth rates.• Faceted, continuous TiO2 surface, mixed TiO2+SiO2
subscale (not effective), then ‘intact’ SiC+TiO2
• (No guarantee of moisture resistance)