Upload
others
View
10
Download
0
Embed Size (px)
Citation preview
National Aeronautics and Space Administration
www.nasa.gov 2
Phase Stability and Thermal Conductivity of Composite Environmental Barrier Coatings on SiC/SiC Ceramic
Matrix Composites
Advanced environmental barrier coatings are being developed to protect SiC/SiC
ceramic matrix composites in harsh combustion environments. The current coating
development emphasis has been placed on the significantly improved cyclic durability and
combustion environment stability in high-heat-flux and high velocity gas turbine engine
environments. Environmental barrier coating systems based on hafnia (HfO2) and
ytterbium silicate, HfO2-Si nano-composite bond coat systems have been processed and
their stability and thermal conductivity behavior have been evaluated in simulated turbine
environments. The incorporation of Silicon Carbide Nanotubes (SiCNT) into high stability
(HfO2) and/or HfO2-silicon composite bond coats, along with ZrO2, HfO2 and rare earth
silicate composite top coat systems, showed promise as excellent environmental barriers
to protect the SiC/SiC ceramic matrix composites.
https://ntrs.nasa.gov/search.jsp?R=20110008738 2020-07-11T18:12:51+00:00Z
National Aeronautics and Space Administration
www.nasa.gov 1
Phase Stability and Thermal Conductivity of Composite Environmental Barrier Coatings on
SiC/SiC Ceramic Matrix Composites
Samantha Benkel *1, 2 and Dongming Zhu 1
1 Durability and Protective Coatings BranchStructures and Materials Division
NASA Glenn Research CenterCleveland, Ohio 44135
2 Carnegie Mellon UniversityPittsburgh, Pennsylvania
The 35th International Conference on Advanced Ceramics & CompositesDaytona Beach, Florida
January 23-28, 2011
This work was supported by NASA Fundamental Aeronautics Program and * NASA LERCIP Internship Program
National Aeronautics and Space Administration
www.nasa.gov 3
Motivation• Environmental barrier coatings (EBCs) for light-weight SiC/SiC ceramic
matrix composite (CMC) components critical for advanced propulsion engines
• Higher temperature and higher strength capable coatings highly desirable
• Composite environmental barrier coatings have promise for improved temperature capability, stability and performance
– High temperature stability is still of concern– HfO2-Si and HfO2-SiCNT bond coats as a major emphasis– HfO2-Yb2Si2O7 and/or HfO2-Yb2SiO5 top coats
• Advanced coating systems were also tested
Underlying SiC/SiC CMC
Composite bond coats
Composite top CoatingIntermediate Coating
National Aeronautics and Space Administration
www.nasa.gov 4
Outline
• Synthesis of Silicon Carbide Nanotubes (SiCNT)– Process optimization and scale up– TGA stability study in air
• Furnace Testing of Hot-Processed HfO2-Si and HfO2-SiCNT Composite Systems– Phase stability at 1400-1450°C
• Thermal Conductivity of HfO2-Si and HfO2-SiCNT systems
• High Pressure Burner Rig (HPBR) Stability of EBC-CMCs
• Cyclic Durability of Advanced Coating-CMC systems
National Aeronautics and Space Administration
www.nasa.gov 5
Experimental• SiC nanotubes synthesized by Si reaction
with multiwall carbon nanotubes (CNTs)at 1400°C in Ar + H2 environments
• Materials/specimens (hot-press): 1”diameter x ~3 mm thick HfO2+Si andHfO2+SiCNT disc specimens or coatingHfO2+Si and HfO2+SiCNT specimens onCMCs
• Furnace stability testing in air byThermogravimetric Analysis (TGA)
• X-ray diffraction and SEMcharacterization
• 3500 W continuous wave (cw) CO2 laser(10.6 micron wavelength) used for hightemperature thermal conductivity testingand high heat flux cyclic durability testing
• High Pressure Burner Rig StabilityTesting
Laser test rig
High Pressure Burner Rig
National Aeronautics and Space Administration
www.nasa.gov 6
SiCNT Processing and Stability Testing• Optimized SiCNT processing with Si to Carbon nanotube (CNT) weight ratio
55:45 for environmental barrier coating applications• Obtained almost full β-SiC phase for the SiCNT based on X-ray diffraction• Retained excellent nanotube morphologies based on SEM characterizations• Scaled up the process with increased High quality SiCNT yields at 0.2 g/batch• Demonstrated SiCNT stability in air using TGA
Ar+5%H2 Ar+5%H2
0
20
40
60
80
100
0 20 40 60 80 100
SiCNTCNT
Wei
ght c
hang
e, %
Time, hours
800ºC, in air
SiCNT processing and TGA stability evaluation SEM and EDS characterizations of SiCNTs
National Aeronautics and Space Administration
www.nasa.gov 7
Laser Steady-State Heat Flux Thermal Conductivity Testing Approach
Schematic of the laser heat flux test principles
Pyrometer
Uniformly distributed laser beam through an integrated
lens
Pyrometer
Specimen fixture
Cooling air nozzle
National Aeronautics and Space Administration
www.nasa.gov 8
Furnace Testing of Hafnia-Silicon Systems
• Optimum mixture composition found between 25wt% and 50wt%Si
Temperature HfO2+25%Si HfO2+50%Si HfO2+75%Si
1350˚C
1400˚
1450˚C
National Aeronautics and Space Administration
www.nasa.gov 9
The HfO2+SiCNT Bond Coats Showed High Temperature Stability in Oxidizing Environments
• HfO2, SiCNT and HfO2 silicate are major phases after the 100hr testing
0
5000
1 104
1.5 104
2 104
2.5 104
10 20 30 40 50 60 70 80
HfO2-18wt%SiCNT after 100 hr test
β-SiC
HfO2
HfSiO4
0
5000
1 104
1.5 104
2 104
2.5 104
Rel
ative
Inte
nsity
Rel
ative
Inte
nsity
Diffraction angle, 2θ
Before Testing + 1400˚C/50hr + 1450˚C/50hr
SiC nanotube (SiCNT) and HfO2-based nano-composite coatings
HfO2-SiCNT composite coating
SiCNT
National Aeronautics and Space Administration
www.nasa.gov 10
The HfO2+Si Bond Coats Showed Significantly Improved Temperature Capability
• Higher stability observed even after 1450ºC testing
Cross-section, Hot-pressed HfO2-50wt%Si on CMC, 1350°C tested
0
1 104
2 104
3 104
4 104
5 104
6 104
10 20 30 40 50 60 70 80
HfO2-25wt%Si-1350°C
HfO2-50wt%Si-1350°C
HfO2-75wt%Si-1400°C
HfO2SiHfSiO4
-1 104
0
1 104
2 104
3 104
4 104
5 104
6 104
Rel
ativ
e In
tens
ity
Rel
ativ
e In
tens
ity
Diffraction angle, 2θ
1350°C 1400°C 1450°C
HfO2-HfO2+30Si bond coat on CMC,
1500°C tested for 200 hours
National Aeronautics and Space Administration
www.nasa.gov 11
High Pressure Burner Rig Recession Testing
• HfO2/ytterbium silicate/HfO2-Si composite bond coat tested at 200 m/s in high pressure burner rig and showed excellent stability
0.0001
0.001
0.01
0.1
1
10
0.0005 0.00055 0.0006 0.00065 0.0007 0.00075 0.0008
SiC/SIC CMCBSASBSAS (200m/s)HfO
2-1 (200 m/s)
Tyranohex SA SiC composite (200m/s)
Spec
ific
wei
ght c
hang
e, m
g/cm
2 -h
1/T, K-1
1300Temperature, °C
14001500 12001600
HfO2-(Y,Gd,Yb) 2O3+Yb2Si2O7/ Yb2Si2O7+20BSAS/ HfO2+30wt%Si (200m/s)
No detectable weight loss, after the 5 hr HPBR Testing
HfO2-(Y,Gd,Yb) 2O3+Yb2Si2O7/ Yb2Si2O7+20BSAS/ HfO2+30wt%Si on the test rig
National Aeronautics and Space Administration
www.nasa.gov 12
High Heat Flux Thermal Gradient Cyclic Durability Evaluation of Environmental Barrier Coating and Bond
Coat Systems• Laser high heat flux rig thermal gradient thermal cyclic testing at surface
temperature of 1482°C (2700°F)• Advanced bond coats tested at up to 1375°C
HfO2-ytterbium silicate coating with HfO2-Si bond coat, after
100hr testing at Tsurface1482°C/Tinterface 1375°C
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 20 40 60 80 100 120 140
8YSZ_mullite_mullite-BSAS_SiHfO2-YbS2_YbS2_BSAS_HfO2-SiEB-YSZGdYb_HfO2-YbS2_YbS2+BSAS_SiYbS+HfO2_YbS-BSAS_HfO2-Si-SiCNT
Ther
mal
con
duct
ivity
, W/m
-K
Time, hours
Tsurface 1482°C/Tinterface 1375°C
Tsurface 1482°C/Tinterface 1175°C
Tsurface 1482°C/Tinterface 1375°C
Tsurface 1482°C/Tinterface 1175°C
National Aeronautics and Space Administration
www.nasa.gov 13
Thermal Conductivity of HfO2-12.4wt%SiCNT
• Effect of nanotube fractions on thermal conductivity is being evaluated and modeled
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
50
100
150
200
0 200 400 600 800 1000 1200 1400
kcera
qthru, w/cm2Ther
mal
con
duct
ivity
, W/m
-K
Hea
t flu
x, W
/cm
2
Surface Temperature, ºC
National Aeronautics and Space Administration
www.nasa.gov 14
Thermal Conductivity of HfO2-Si Systems• Thermal conductivity maintained stable after high temperature 100 hr
annealing
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0
50
100
150
200
0 200 400 600 800 1000 1200
kcera
qthruTher
mal
con
duct
ivity
, W/m
-K
Hea
t flu
x, W
/cm
2
Surface Temperature, ºC
HfO2+50Si on CMC 1450C pre-annealed
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0
50
100
150
200
0 200 400 600 800 1000 1200
kcera
qthruTher
mal
con
duct
ivity
, W/m
-K
Hea
t flu
x, W
/cm
2
Surface Temperature, ºC
HfO2+25Si on CMC 1450C pre-annealed
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
-50
0
50
100
150
200
0 200 400 600 800 1000 1200 1400
kcera
qthru, w/cm2Ther
mal
con
duct
ivity
, W/m
-K
Hea
t flu
x, W
/cm
2
Surface Temperature, ºC
HfO2+25Si free standing
National Aeronautics and Space Administration
www.nasa.gov
Summary
• Composite HfO2-Si and HfO2-SiCNT bond coats synthesized for high temperature environmental barrier coating applications
• The stability of HfO2-Si and HfO2-SiCNT bond coats demonstrated for stability up to 1450°C (1500°C for advanced processed coatings)
• Thermal conductivity of HfO2-Si and HfO2-SiCNT bond coats evaluated
• Multilayer EBC composite coatings showed combustion gas stability and thermal gradient durability in high pressure burner rig and laser high heat flux rig
National Aeronautics and Space Administration
www.nasa.gov
AcknowledgementsThe work was supported by NASA Fundamental
Aeronautics Program (FAP) Supersonics Project (Manager: Dale A. Hopkins) and NASA Integrated Systems Research Program (ISRP) Environmentally Responsible Aviation (ERA) Project (Manager: Janet Hurst).
The authors wish to thank Ms. Joyce A. Dever, Chief of Durability and Protective Coatings Branch, for her kind help and support in the research during the NASA Internship project.
Also Many Thanks to:• Bob Angus (Hot Press Operation)• Dr. Richard Rogers (X-ray Diffraction)• Terry McCue (SEM)• Don Humphrey, SiCNT TGA• Dennis Fox, EBC coating processing• Bob Pastel, High Pressure Burner Rig testing• NASA Lewis' Educational and Research Collaborative
Internship Project (LERCIP)
NASA Supersonics
NASA Subsonics/ERA