NASA Technical Reports Server (NTRS) 20110008749: Creep Behavior of Hafnia and Ytterbium Silicate Environmental Barrier Coating Systems on SiC/SiC Ceramic Matrix Composites

6.2 MB·English

by  NASA Technical Reports Server (NTRS)

Creep Behavior of Hafnia and Ytterbium Silicate Environmental
Barrier Coating Systems on SiC/SiC Ceramic Matrix Composites

Environmental barrier coatings will play a crucial role in future advanced gas turbine engines
because of their ability to significantly extend the temperature capability and stability of SiC/SiC
ceramic matrix composite (CMC) engine components, thus improving the engine performance. In
order to develop high performance, robust coating systems for engine components, appropriate test
approaches simulating operating temperature gradient and stress environments for evaluating the
critical coating properties must be established. In this paper, thermal gradient mechanical testing
approaches for evaluating creep and fatigue behavior of environmental barrier coated SiC/SiC CMC
systems will be described. The creep and fatigue behavior of Hafnia and ytterbium silicate
environmental barrier coatings on SiC/SiC CMC systems will be reported in simulated
environmental exposure conditions. The coating failure mechanisms will also be discussed under
the heat flux and stress conditions.
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Dongming Zhu*, Dennis S. Fox*, Louis J. Ghosn** and Bryan Harder*
* Durability and Protective Coatings Branch, Structures and Materials Division
** Applied Structural Mechanics Branch, Mechanical and Fluid Systems Division
NASA John H. Glenn Research Center
Cleveland, Ohio 44135, USA
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January 23-28, 2011
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Revolutionary Ceramic Coatings and Composites Impact
TTuurrbbiinnee EEnnggiinnee TTeecchhnnoollooggyy
– Advanced environmental barrier coatings and SiC/SiC CMC combustor and
turbine airfoil component technologies are being developed for reduced cooling
and NO emission under NASA programs
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– Next generation environmental barrier coating-CMC development require more
sophisticated laboratory testing to simulate turbine engine temperature and
stress environments
Instability
CMC
Control
Fuel Liners
Staging
Multipoint
Injection
Low emission combustor
Advanced core technologies – HPT first stage
CCMMCC vane wiitthh siigniiffiicanttlly redduce coolliing
requirements
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NASA Environmental Barrier Coating – CMC System
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• Emphasize temperature capability, performance and durability requirements
• Help fundamental understanding, database and design tool development
• Increase the coatingg Technologgyy Readiness Levels for enggine apppplications
Current NASA Program Goals
Step increase in the material’s temperature capability
TTeemmppeerraattuurree - 3000°F* SiC/SiC CMC
combustor and turbine vane
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- 2800°F* ERA combustor EBC
Combustor
2700°F (1482C)
TBC (APS)
- 2700°F* SiC/SiC CMC blade
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2500°F - 2600°F* ERA turbine vane EBC
Turbine TBC
(EB-PVD)
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2400°F (1316°C)
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2000°F (1093°C)
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Challenges:
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* Recession: <5 mg/cm2 per 1000 hr (40-50 atm, Mach 1~2)
** Component strength and toughness requirements
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Outline
─ Advanced creep and fatigue testing development for environmental
barrier coating – CMC systems
• Higgh heat flux thermal fatiggue test rigg – ppast expperience
• New heat flux mechanical test rigs
• High heat flux tensile creep rupture rig
• High heat flux ball-on-ring creep/fatigue test rigs
•• FFEEMM aannaallyyssiiss aanndd mmooddeell vvaalliiddaattiioonn
─ Creep testing of candidate model environmental barrier coating
systems for SiC/SiC CMC airfoils and combustors
• YYtttterbbiium siilliicatte
• HfO and HfO Rare Earth Aluminosilicate EBCs
2 2
• The coating degradation and delamination under thermal cycle and
creep conditions
─ Preliminary failure mechanisms and modeling
─ Summary
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Laser High Heat Flux Approach
– Turbine level high-heat-flux tests crucial for CMC coating system developments
• Existing high heat testing High power CO laser high-heat-flux rig (up to 315 W/cm2)
2
Turbine: 450°F across 100 microns
Combustor:1250°F across 400 microns
Heat flux
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Real-Time Thermal Conductivity Measurements
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Optional miniature
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thermocouple for
m pyrometers for qq
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additional heat-flux
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Typical Thermal Cyclic Behavior of EBC Systms
– Sintering and delaminations of coatings reflected by the apparent thermal
conductivity changes
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8YSZ/mullite/mullite+20wt%BSAS/Si on SiC/SiC:
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Time, hours
7
Delamination in a High Heat Flux Thermal Cycling
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pp
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00..0000 00..0055 00..1100 00..1155 00..2200
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The FEM model
8
Experimental:
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- Integrated with a High Power CO laser system
2
- Allows very high temperature, high heat flux cooled thermal gradient testing
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- Accommodates conventional 6” tensile dog-bone and also other configuration
specimens
- Specifically designed for CMC turbine airfoil system development
Laser beam
delivery optic
ssyysstteemm CCoooolliinngg sshhooweerr
head jets
High temperature
extensometer
Test specimen
9