NASA/TMm2001-211122
`
`Thermal
`Barrier
`
`Conductivity
`and Environmental
`
`of Ceramic
`Barrier
`
`Thermal
`
`Coating Materials
`
`Zhu
`Dongming
`Ohio Aerospace
`
`Institute,
`
`Brook
`
`Park, Ohio
`
`Narottam
`Glenn
`
`P. Bansal
`Research
`Center,
`
`Cleveland,
`
`Ohio
`
`Kang N. Lee
`Cleveland
`State University,
`
`Cleveland,
`
`Ohio
`
`Robert
`Glenn
`
`A. Miller
`Research
`
`Center,
`
`Cleveland,
`
`Ohio
`
`September
`
`2001
`
`1
`
`UTC 2024
`General Electric v. United Technologies
`IPR2016-01289
`
`

`

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`

`

`NASA/TM--2001-211122
`
`Thermal
`Barrier
`
`Conductivity
`and Environmental
`
`of Ceramic
`Barrier
`
`Thermal
`
`Coating Materials
`
`Zhu
`Dongming
`Ohio Aerospace
`
`Institute,
`
`Brook
`
`Park, Ohio
`
`Narottam
`Glenn
`
`P. Bansal
`Research
`Center,
`
`Cleveland,
`
`Ohio
`
`Kang N. Lee
`Cleveland
`State University,
`
`Cleveland,
`
`Ohio
`
`Robert
`Glenn
`
`A. Miller
`Research
`
`Center,
`
`Cleveland,
`
`Ohio
`
`National
`
`Aeronautics
`
`and
`
`Space Administration
`
`Glenn
`
`Research
`
`Center
`
`September
`
`2001
`
`3
`
`

`

`Acknowledgments
`
`by NASA Ultra-Efficient
`supported
`This work was
`at NASA Glenn Research
`George W. Leissler
`TBC and EBC coatings
`specimens.
`Thanks
`various
`
`Engine Technology
`Center
`for his assistance
`are due
`to John Setlock
`ceramic
`compositions.
`
`Program.
`(UEET)
`in the preparation
`for his help with
`
`The authors
`are grateful
`of plasma-sprayed
`hot pressing
`of
`
`to
`
`or manufacturers'
`report
`in this
`are used
`names
`names
`Trade
`not constitute
`an official
`does
`only. This usage
`identification
`implied,
`by the National
`or
`either
`expressed
`endorsement,
`Aeronautics
`and Space Administration.
`
`for
`
`for Aerospace
`NASA Center
`Drive
`7121 Standard
`Hanover, MD 21076
`
`Information
`
`National
`
`Technical
`
`Information
`
`Service
`
`5285 Port Royal Road
`Springfield,
`VA 22100
`
`Available
`
`from
`
`Available
`
`electronically
`
`at http://gltrs.grc.nasa.gov/GLTRS
`
`4
`
`

`

`THERMAL
`CONDUCTIVITY
`ENVIRONMENTAL
`
`BARRIER
`THERMAL
`OF CERAMIC
`BARRIER
`COATING
`MATERIALS
`
`AND
`
`Dongming
`
`Zhu, Narottam P. Bansal, Kang N. Lee and Robert A. Miller
`National
`Aeronautics
`and Space Administration
`Glenn Research
`Center
`Cleveland,
`Ohio 44135
`
`ABSTRACT
`
`been
`have
`EBC's)
`and
`(TBCs
`coatings
`barrier
`environmental
`and
`barrier
`Thermal
`from high
`engines
`turbine
`in gas
`components
`ceramic
`and Si-based
`developed
`to protect metallic
`based
`(BSAS)/mullite
`and
`(Ba,Sr)AlzSi_,Os
`oxides
`temperature
`attack.
`Zirconia-yttria
`based
`values
`of
`conductivity
`In this
`study,
`thermal
`have
`silicates
`been
`used
`as the
`coating materials.
`at high temperatures
`zirconia-yttria-
`and BSAS/mullite-based
`coating materials
`were
`determined
`test,
`the
`specimen
`using
`a steady-state
`laser
`heat
`flux
`technique.
`During
`the
`laser
`conductivity
`surface
`was heated
`by delivering
`uniformly
`distributed
`heat
`flux from a high power
`laser. One-
`dimensional
`steady-state
`heating
`was
`achieved
`by
`using
`thin
`disk
`specimen
`configuration
`(25.4 mm diam and
`2 to
`4 mm thickness)
`the
`appropriate
`backside
`air-cooling.
`The
`
`and
`
`temperature
`backside
`temperature
`corrections
`specimen
`
`by two surface
`measured
`carefully
`was
`thickness
`specimen
`the
`across
`gradient
`as
`a function
`determined
`were
`thus
`values
`thermal
`conductivity
`The
`pyrometers.
`heat
`loss and laser
`absorption
`radiation
`I-D heat
`transfer
`equation.
`The
`on the
`based
`measurements.
`The
`effects
`were
`considered
`in the
`conductivity
`of
`the materials
`porosity
`and sintering
`on measured
`conductivity
`values were
`also evaluated.
`
`and
`of
`
`of
`
`INTRODUCTION
`
`been
`have
`(EBC's)
`coatings
`barrier
`Environmental
`temperature
`from high
`engines
`turbine
`components
`in gas
`higher
`significantly
`for
`continuously
`increasing
`demands
`future
`EBC systems
`efficiency
`and better
`engine
`reliability,
`engine
`components
`the
`and
`environmental
`protections
`of
`barrier
`functions
`environment
`[4].
`In particular,
`thermal
`loads
`and
`chemical
`reducing
`engine
`component
`thermal
`the
`required
`mechanical
`properties
`and
`durability
`of
`these
`advanced
`thermal
`barrier
`and
`environmental
`barrier
`coatings
`impact
`the successful
`use of ceramic
`components
`in advanced
`
`ceramic
`Si-based
`to protect
`developed
`attack
`[1-3]. With
`environmental
`temperature,
`fuel
`engine
`operating
`for both
`thermal
`must
`be designed
`combustion
`gas
`in
`gas
`turbine
`a necessity
`for
`of EBC's
`become
`thus maintaining
`reaction
`rates,
`of
`development
`components.
`The
`(TBC's
`and EBC's)
`will
`directly
`engine
`systems.
`
`have
`coatings
`(Ba,Sr)A12Si2Os(BSAS)-mullite
`and
`ZrO2-8 wt% Y203,
`Plasma-sprayed
`and environmental
`for superalloy
`components,
`coatings
`successfully
`used as thermal
`barrier
`been
`respectively.
`In this
`matrix
`composite
`(CMC)
`systems,
`coatings
`for SiC/SiC
`ceramic
`barrier
`a laser
`steady-state
`heat
`flux technique
`is established
`to evaluate
`high temperature
`thermal
`study,
`the
`conductivity
`of
`both
`hot-pressed
`and
`plasma-sprayed
`TBC/EBC
`materials.
`The
`thermal
`conductivity
`data
`are of great
`importance
`for
`future
`advanced
`coating
`design.
`
`NASA/TM--2001-211122
`
`1
`
`5
`
`

`

`MATERIALS
`
`AND EXPERIMENTAL
`
`METHODS
`
`Materials
`
`materials,
`TBC and EBC coating
`Several
`tested
`at
`and mullite+BSAS
`mixtures,
`were
`conductivity
`values
`using
`a laser
`steady
`state
`either
`hot-pressed
`disks
`(25.4 mm diam and
`
`ZrO_,-8 wt% Y203,
`including
`high
`temperatures
`to determine
`heat
`flux test
`technique.
`The
`test
`2 to 4 mm thickness),
`or
`254
`
`BSAS, mullite,
`their
`thermal
`specimens
`were
`to 400-1am
`thick
`
`powders
`spray-dried
`using
`fabricated
`were
`specimens
`The hot-pressed
`coatings.
`plasma-sprayed
`by plasma-
`were prepared
`specimens
`coating
`under
`30 MPa pressure.
`The
`at 1500 °C for an hour
`or on melt-
`onto
`superalloy
`disks
`(25.4 mm diam and
`3.2 mm thickness)
`spraying
`the powders
`infiltrated
`(MI)
`SiC/SiC
`ceramic
`matrix
`composites
`(25.4 mm diam and
`2.2 mm thickness)
`substrates.
`
`Thermal
`
`Conductivity
`
`Testing
`
`Thermal
`3.0 kW CO2 laser
`
`conductivity
`(wavelength
`
`testing
`10.6
`
`ceramic
`the
`of
`lain ) high-heat
`
`materials
`coating
`flux
`rig. A schematic
`
`carried
`was
`diagram
`
`out
`of the
`
`using
`test
`
`a
`rig
`
`approaches
`test
`the general
`1, and
`in Fig.
`illustrated
`are
`facilities
`test
`actual
`the
`of
`photos
`and
`conductivity
`flux
`thermal
`In this
`steady-state
`laser
`heat
`[5-9].
`elsewhere
`described
`been
`have
`was provided
`by the laser
`beam,
`and backside
`air-cooling
`was
`surface
`heating
`the
`specimen
`test,
`the desired
`specimen
`temperatures.
`A uniform laser
`heat
`flux was obtained
`over
`used to maintain
`the
`23.9 mm diam aperture
`region
`the
`specimen
`surface
`by using
`an integrating
`ZnSe
`lens
`combined
`with the specimen
`rotation.
`Platinum
`wire
`flat
`coils
`(wire
`diam 0.38 mm) were
`used to
`form thin
`air gaps
`between
`the
`top
`aluminum
`aperture
`plate
`and
`stainless-steel
`back
`plate
`to
`minimize
`the specimen
`heat
`losses
`through
`the fixture.
`
`of
`
`The
`
`thermal
`
`conductivity
`
`kcerami
`
`c of
`
`the
`
`ceramic
`
`materials
`
`can
`
`be determined
`
`from the
`
`pass-through
`
`heat
`
`flux
`
`qthru and measured
`
`temperature
`
`difference
`
`ATcerami
`
`c
`
`across
`
`the
`
`ceramic
`
`specimen
`conditions
`
`the
`(or
`[5, 7]
`
`ceramic
`
`coating)
`
`thickness
`
`lcerami
`
`c
`
`under
`
`the
`
`steady-state
`
`laser
`
`heating
`
`k ceramic = q thru "l ceramic
`
`/ ATceramic
`
`( 1)
`
`obtained
`
`by
`
`The
`
`actual
`
`pass-through
`
`heat
`
`flux
`
`qthru
`
`for
`
`a given
`
`ceramic
`
`specimen
`
`was
`
`subtracting
`radiation
`
`the
`heat
`
`loss
`reflection
`laser
`loss
`(total
`emissivity
`
`(measured
`was
`taken
`
`and
`by a 10 ktm reflectometer)
`as 0.50 for
`the oxides
`and silicates)
`
`the
`at
`
`calculated
`the ceramic
`
`coating
`
`surface
`
`(i.e.,
`
`qthru = qdelivered --qreflected --qradiated ) from the
`
`laser
`
`delivered
`
`heat
`
`flux.
`
`that
`Note
`surfaces
`
`the
`because
`
`non-reflected
`of
`the
`
`quite
`
`laser
`high
`
`is
`energy
`emissivity
`
`assumed
`at
`the
`
`at or near
`absorbed
`to be
`10.6 _tm laser wavelength
`
`the
`region
`
`specimen
`for
`the
`
`oxides
`
`and
`
`silicates.
`
`In some
`
`test
`
`cases,
`
`the
`
`pass-through
`
`heat
`
`flux
`
`q,h,_ was
`
`verified
`
`with
`
`internal
`embedded
`
`flux
`heat
`miniature
`
`incorporated
`gauge
`thermocouple.
`
`with
`For
`the
`
`the
`hot
`
`substrates
`pressed
`
`(instrumented
`bulk
`specimens,
`
`via
`specimens)
`the
`temperature
`
`an
`
`an
`
`NASA/TM--2001-211122
`
`2
`
`6
`
`

`

`difference
`
`AT, vr.mi ,.
`
`in the
`
`ceramic
`
`was
`
`directly
`
`measured
`
`by
`
`using
`
`surface
`
`and
`
`backside
`
`pyrometers
`and
`at 0.97
`
`pyrometers,
`8 pm infrared
`(both
`for mullite
`and BSAS
`silicates).
`
`emissivity
`For
`
`set
`was
`coating
`
`oxides.
`for ZrO2-Y203
`at 0.94
`specimens,
`the
`temperature
`
`the
`
`difference
`
`in the
`
`ceramic
`
`coating
`
`AT_.er.,,,i,. was obtained
`
`from the measured
`
`coating
`
`surface
`
`and
`
`substrate
`respectively,
`
`using
`temperatures
`backside
`and subtracting
`the temperature
`
`an
`
`8 um pyrometer
`drops
`in the substrate
`
`two-color
`a
`and
`and bond coat
`
`pyrometer,
`
`ATcer.,,,,c
`
`= Tceramic-surqfi'e-
`
`T,',,bst,'ate-back
`
`10
`
`_li_
`
`_ fl_o,,a
`
`qthru
`
`" dl
`
`qth,-u
`
`dl
`
`k s,tl_strate(T )
`
`where
`
`and
`
`T_.ubstrate_l_ack
`
`are measured
`
`ceramic:
`
`surface
`
`and
`
`substrate
`
`backside
`
`L'eramic-surqlce
`
`temperatures,
`
`lboml,
`
`1
`
`sllb_D'afC
`
`,
`
`and
`
`kl, ond(T)
`
`and
`
`k
`
`(T_
`
`are
`
`the
`
`thicknesses
`
`and
`
`the
`
`_ltt)_D'Ug('
`
`temperature-dependent
`
`thermal
`
`conductivity
`
`of the bond coat
`
`and substrate,
`
`respectively.
`
`RESULTS
`
`AND DISCUSSION
`
`Phase Structures
`
`of Coating Materials
`
`the
`
`of ZrO2-8 wt% Y203, BSAS,
`results
`diffraction
`X-ray
`typical
`2 shows
`Figure
`hot-pressed
`ZrO2-8 wt% Y203
`had
`and
`plasma-sprayed
`The
`materials.
`BSAS+mullite
`phases
`after
`the processing
`and
`the
`laser
`some monoclinic
`and cubic
`t' phase with
`tetragonal
`and
`cubic
`phases were
`usually
`present
`conductivity
`testing. However,
`more monoclinic
`thermal
`due to the lower
`processing
`temperature.
`in the hot-pressed
`ZrO2-8 wt% Y203 specimen
`probably
`showed
`mainly
`the
`(Ba,Sr)Al2Si2Os
`Both
`hot-pressed
`and
`plasma-sprayed
`BSAS
`specimens
`celsian
`phase.
`The BSAS+mullite
`mixture
`specimen
`contained
`both the
`(Ba,Sr)Al2Si208
`celsian
`and mullite
`phases,
`as expected.
`
`and
`a
`
`Thermal
`
`Conductivity
`
`of ZrOz-8 wt % YzOa
`
`thermal
`the
`used
`is extensively
`(2I"O2-4.55 mol%)
`ZrO2-8 wt% Y203
`mechanical
`excellent
`low thermal
`conductivity
`and
`because
`of
`its
`material
`test
`temperature
`conductivity
`of a hot-pressed
`specimen
`as a function
`of
`thermal
`Fig. 3 (a). The
`dense
`bulk material
`a conductivity
`value
`of 2.0 to 2.3 W/m-K,
`only slight
`temperature
`dependence.
`
`had
`
`as
`
`coating
`barrier
`The
`properties.
`in
`is shown
`and
`showed
`
`The
`
`thermal
`
`conductivity
`
`of a 180-I, tm thick,
`
`plasma-sprayed
`
`ZrO2-8 wt% Y203
`
`coating
`
`superalloy
`based
`on a nickel
`specimen
`porous, microcracked
`thermal
`relatively
`1316 °C for
`temperature
`of
`surface
`of
`conductivity
`value
`1.0 W/m-K,
`but
`1.4 W/m-K
`due to the ceramic
`sintering.
`
`substrate
`barrier
`20 hr.
`after
`
`as a function
`coating
`(with
`can
`seen
`It
`20 hr
`testing
`
`be
`laser
`
`is shown
`of time
`10 vol% porosity)
`that
`the
`coating
`the
`conductivity
`
`in Fig. 3 (b). The
`was
`tested
`at a
`had
`an
`initial
`increased
`to
`
`NASA/TM--2001-211122
`
`3
`
`7
`
`

`

`Thermal
`
`Conductivity
`
`of BSAS
`
`and Mullite
`
`results
`test
`conductivity
`the thermal
`4 shows
`Figure
`thermal
`The measured
`flux
`technique.
`heat
`the
`laser
`using
`of
`temperature
`range
`2.8
`to 3.0 W/m-K
`in the
`about
`conductivity
`during
`the heating
`cycle
`is due
`to possible
`results
`are
`consistent
`with
`the
`conductivity
`measurements
`
`of a hot-pressed
`conductivity
`800
`to
`1400°C.
`specimen
`cracking.
`of
`a laser
`sintered,
`
`BSAS
`disk specimen
`specimen
`was
`of
`this
`A sudden
`drop
`in
`The
`conductivity
`254-_tm
`thick
`
`substrate
`superalloy
`base
`on a nickel
`specimen
`coating
`dense BSAS
`also be seen that
`thermal
`conductivity
`of a 254- _tm thick plasma-sprayed
`
`it can
`(Fig. 5). From Fig. 5,
`mullite
`coating
`showed
`
`stronger
`temperature
`temperature
`
`temperature
`regime.
`range
`
`than BSAS.
`dependence
`coating
`had
`The mullite
`of 1000 to 1400 °C.
`
`conductivity
`Lower
`conductivity
`values
`
`values were measured
`of-1.9
`to 2.5 W/m-K
`
`at high
`in the
`
`initial
`the
`coating,
`BSAS
`plasma-sprayed
`as
`the
`For
`As shown
`of higher
`porosity.
`due
`to the presence
`lower
`significantly
`of BSAS was
`about
`1.4 W/m-K
`at 900 °C. Considerable
`conductivity
`during
`the
`first
`heating-cooling
`cycle
`due
`to the
`ceramic
`observed
`to -2.2 W/m-K at 900 °C.
`cycle,
`the conductivity
`increased
`
`be
`can
`values
`conductivity
`thermal
`the initial
`in Fig. 6,
`conductivity
`increase
`was
`sintering.
`After
`the
`first
`test
`
`Thermal
`
`Conductivity
`
`of BSAS
`
`and Muilite Mixtures
`
`thermal
`the
`7 shows
`Figure
`using
`the
`disk specimens
`for
`the
`two materials
`were
`
`and mullite
`BSAS
`of hot-pressed
`results
`test
`conductivity
`conductivity
`thermal
`The measured
`laser
`heat
`flux technique.
`about
`3.0 W/m-K
`at 600 °C and
`1.6 to 2.0 W/m-K at 1500 °C.
`
`mixture
`values
`
`higher
`slightly
`A
`(30 wt% BSAS+70mullite)
`
`conductivity
`material.
`
`was
`
`observed
`
`for
`
`the
`
`higher
`
`BSAS
`
`containing
`
`to the
`Similar
`also
`coatings
`the
`254-_tm
`
`+ mullite
`BSAS
`plasma-sprayed
`the
`coating,
`BSAS
`sprayed
`plasma
`shown
`in
`value
`due
`to porosity.
`As
`initial
`conductivity
`lower
`showed
`thick mullite+20wt%
`BSAS
`coating
`had
`an
`initial
`conductivity
`of
`
`mixture
`Fig. 8,
`
`1.5 W/m-K,
`However,
`coating.
`
`to 2.0 W/m-K
`and increased
`coating
`had less
`conductivity
`
`the
`
`at 900 °C after
`increase
`due
`
`cycle
`first heating
`the
`to sintering
`as compared
`
`to sintering.
`due
`to pure BSAS
`
`Thermal
`
`Conductivity
`
`of TBC/EBC
`
`Systems
`
`also
`was
`systems
`of TBC/EBC
`conductivity
`Thermal
`results
`of a two-layer
`BSAS/mullite+20
`conductivity
`test
`thermal
`CMC
`substrate.
`The
`first
`heating-cooling
`on
`the
`SiC/SiC
`coated
`to the
`larger
`initial
`ceramic
`sintering.
`due
`conductivity
`increase
`much
`less
`conductivity
`increase.
`This
`cycle,
`however,
`showed
`temperatures,
`most of the sintering
`and densification
`had occurred
`
`the
`9 shows
`Fig.
`investigated.
`coating
`that was
`wt% BSAS
`had
`a
`significant
`cycle
`heating-cooling
`second
`The
`the
`given
`at
`is because
`during
`the first cycle.
`
`test
`
`NASA/TM--2001-211122
`
`4
`
`8
`
`

`

`In order to evaluate muitilayer TBC/EBC coating conductivity information at high
`temperature,a ZrO2-8wt% Y203/mullite/Si/SiC-SiCCMC system was tested at a surface
`temperatureof 1560°C with a laserpass-thruheat flux of 115W/m-K. Figure 10 (a) and (b)
`show the coatingthermal conductivity, and the estimatedtemperaturedistribution acrossthe
`coatingsystem.Theoverall initial ceramiccoatingconductivitywasabout 1.6to 1.8W/m-K, but
`theconductivityquickly increasedto about2.2W/m-K afterthe hightemperatureexposurefor a
`short period of
`time. A slight decreasein coating conductivity may be related to some
`microcrackingof thecoatingsystems.Coatingsinteringanddelaminationwill becomeimportant
`issuesfor developingadvancedceramiccoatingsystemsdesignedfor high temperatureandhigh
`thermalgradientapplications.
`
`CONCLUSIONS
`
`thermal
`conductivity
`used to investigate
`has been
`flux technique
`heat
`steady-state
`A laser
`current
`BSAS
`of
`the
`conductivity
`values
`Thermal
`several
`TBC and EBC coating materials.
`of
`as compared
`to
`in the range
`of 1.9 to 3.0 W/m-K,
`and mullite
`based EBC coating materials
`were
`plasma-sprayed
`barrier
`coating
`material.
`The
`-2.0 W/m-K
`for
`the ZrO2-8 wt% Y203
`thermal
`for
`1.0 W/m-K
`(1.4 W/m-K
`for EBCs
`and
`coatings
`showed
`lower
`initial
`conductivity
`values
`due
`to higher
`hot
`ZrO2-8 wt% Y203)
`as
`compared
`to the
`oppressed
`bulk
`coating
`materials
`TBC and EBC
`was
`porosity.
`Significant
`conductivity
`increase
`observed
`for
`the plasma-sprayed
`coating
`systems
`after
`the
`laser
`high temperature
`thermal
`exposure
`because
`of ceramic
`sintering
`and densification.
`
`REFERENCES
`
`Durability
`Surface
`
`and
`of Mullite
`and Coatings
`
`for
`
`Ceramics,"
`
`and Environmental
`"Development
`and R.A. Miller,
`K.N. Lee
`Dual Layer Coatings
`for SiC and Si3N4 Ceramics,"
`Mullite/YSZ
`vol. 86-87,
`pp. 142-148,
`1996.
`Technology,
`Barrier Coatings
`Environmental
`"Key Durability
`Issues with Mullite-Based
`K.N. Lee,
`2000.
`122, pp. 632-636,
`Si-Base Ceramics,"
`vol.
`Transactions
`of the ASME,
`Coatings
`for Si-Based
`K.N. Lee,
`"Current
`Status
`of Environmental
`Barrier
`vol.
`133-134,
`pp. 1-7, 2000.
`Surface
`and Coatings
`Technology,
`D. Zhu, K.N. Lee,
`and R.A. Miller,
`"Thermal
`Conductivity
`and Thermal
`Behavior
`of Refractory
`Silicate
`Coatings
`on SiC/SiC
`Ceramic
`Matrix
`NASA TM-210824,
`NASA Glenn Research
`Center, Cleveland,
`April
`2001.
`D. Zhu
`and R.A. Miller,
`"Thermal
`Conductivity
`and Elastic Modulus
`Thermal
`Barrier
`Coatings
`Under
`High
`Heat
`Flux
`Conditions,"
`NASA
`NASA Glenn Research
`Center, Cleveland,
`Ohio, April
`1999.
`Evolution
`D. Zhu
`and R.A. Miller,
`"Thermal
`Conductivity
`and
`Elastic Modulus
`of Thermal
`Thermal
`Barrier
`Coatings
`Under High Heat Flux Conditions,"
`Journal
`vol. 9, pp. 175-180,
`2000.
`Technology,
`Thermal
`of Ceramic
`Change
`D. Zhu
`and R.A. Miller,
`"Thermal
`Conductivity
`Kinetics
`NASA
`Laser Heat Flux Technique,"
`Barrier
`Coatings
`Determined
`by the Steady-State
`Glenn Research
`Center, Cleveland,
`Ohio, NASA TM-209639,
`Research
`and Technology
`1999, pp. 29-31, March
`2000.
`
`Cyclic
`Gradient
`Composites,"
`
`Evolution
`TM-209069,
`
`of
`
`of
`Spray
`
`[1]
`
`[21
`
`[3]
`
`[4]
`
`[5]
`
`[61
`
`[7]
`
`NASA/TM--2001-211122
`
`5
`
`9
`
`

`

`[8]
`
`[9]
`
`"Thermal
`D. Zhu and R.A. Miller,
`vol. 27, pp. 43--47,
`MRS Bulletin,
`D. Zhu, R.A. Miller,
`B.A. Nagaraj,
`Thermal
`Barrier
`Coatings
`Evaluated
`vol.
`
`Surface
`
`and Coath_gs
`
`Technology,
`
`Coatings
`
`for Advanced
`
`Barrier
`2000.
`"Thermal
`and R.W. Bruce,
`by a Steady-State
`Laser
`138, pp. 1-8, 2001.
`
`Gas-Turbine
`
`Engines,"
`
`Conductivity
`Heat
`Flux
`
`of EB-PVD
`Technique,"
`
`Laser beam/
`
`integrating
`
`lens
`
`Reflectometer_"
`
`300 rpm
`
`Specimen
`
`I
`
`3.0 kW CO 2 high power
`
`laser
`
`J
`
`Pyrometers
`
`Air gap
`
`Platinum flat coils
`
`Aluminum laser
`
`aperture
`
`Ceramic
`coating
`Bond coat
`Miniature
`
`thermocouple
`Back aluminum TBC
`coated
`plate edge
`
`Aluminum back
`
`plate
`
`Cooling
`
`air
`
`tube
`
`Metal
`
`_r CMC substrate
`
`Thermocouple
`
`(a)
`
`Slip ring
`
`Cooling
`
`air
`
`(b)
`
`During the test,
`of TBC/EBC materials.
`conductivity
`thermal
`flux rig for determining
`high heat
`Figure 1.wLaser
`temperatures
`are measured
`by infrared pyrometers.
`The
`surface
`and the substrate
`backside
`the ceramic
`thermal
`conductivity
`of the ceramics
`can be determined
`from the pass-through
`heat
`flux and measured
`temperature
`difference
`through
`the ceramic
`specimen
`(or the ceramic
`coating)
`thickness
`under
`the steady-
`state laser heating
`conditions
`by a one-dimensional
`(one-D)
`heat
`transfer model.
`(a) Schematic
`diagram
`laser
`test
`rig;
`(b) A 3.0 kW CO 2 continuous
`wave
`laser system;
`(c) The test
`rig with a ceramic
`specimen
`under
`testing.
`
`NASA/TM--2001-211122
`
`6
`
`10
`
`

`

`....
`
`4
`
`......
`
`t
`
`....
`
`I
`
`''
`
`'
`
`I
`
`....
`
`I
`
`....
`
`(a)
`
`•
`
`Zirconia
`cubic
`
`tetragonal
`phases
`
`and
`
`0 Zirconia monoclinic
`
`phase
`
`II
`F
`i
`
`1400[
`
`....
`
`I
`1200 _
`
`looo
`
`L
`800 _-
`
`¢n
`t-
`
`¢-
`,1
`
`.>
`
`ec
`
`•
`
`•
`
`1
`
`•
`
`ZrO2-8 wt% Y203
`plasma-sprayed
`
`-
`
`ZrO2-8 wt% Y203-hot
`•
`
`pressed
`
`•
`
`i
`200 [-
`
`oll •
`
`_ iO
`
`g
`0
`
`0 ["'":'_"' F"_-,,-.....i_,_,.,_,.,I _-_i_ r_'_'"FA ,-_,"......._.'-_,-,_-',,--_,,_I,__,"-_,.._,+_..i _',"r'i
`
`
`20
`30
`40
`50
`60
`70
`80
`90
`100
`
`Diffraction
`
`angle
`
`2e, deg
`
`8OO
`
`....
`
`I
`
`....
`
`!
`
`....
`
`i
`
`....
`
`I
`
`....
`
`•
`
`I
`
`....
`
`[
`
`....
`
`I
`
`....
`
`• Mullite
`
`(b)
`
`700
`
`600
`
`500
`
`o_
`
`400
`
`.1
`.>_
`
`_
`
`:300
`
`coo
`
`200
`
`100
`
`o
`
`o
`
`0
`
`00[
`
`0
`
`0
`
`•
`
`•
`
`o
`
`_
`
`o
`
`••
`
`o
`
`Mullite + 20wt%
`
`BSAS-hot
`
`pressed
`
`o BSAS celsian
`
`phase
`
`o
`
`o
`
`o
`
`o
`
`0
`
`o
`
`o o
`
`BSAS plasma-sprayed
`
`%0o
`
`o ooooo
`
`0 0 930 0 °°0
`
`0°o
`
`0
`
`0
`
`o
`
`o |
`
`BSAS hot pressed
`
`%0 Jlo.Ooo% oTo oooo
`
`yo
`
`o
`
`0
`
`20
`
`25
`
`30
`
`35
`Diffraction
`
`40
`angle
`
`45
`20, deg
`
`50
`
`55
`
`6O
`
`patterns
`diffraction
`X-ray
`2.nTypical
`Figure
`(b) BSAS,
`and BSAS + mullite materials.
`
`of
`
`(a) ZrO2-8 wt% Y203 , and
`
`NASA/TM--2001-211122
`
`7
`
`11
`
`

`

`]
`
`I
`
`I
`
`I
`
`]
`
`Hot-pressed
`
`specimen
`
`0
`
`0
`
`0
`
`0
`
`o
`
`0
`
`0
`
`4.0
`
`3.5
`
`3.0
`
`2.5
`
`2.0
`
`1.5
`
`1.0
`
`.m
`._>
`
`t-
`O
`
`e-
`l--
`
`0.5
`
`0.0
`
`200
`
`400
`
`600
`Test
`
`800
`temperature,
`
`1000
`"C
`
`1200
`
`1400
`
`1316 °C
`
`plasma-sprayed
`
`coating
`
`2O
`
`of ZrO2-8 wt% Y203 determined
`conductivity
`Figure 3.--Thermal
`by
`of
`technique.
`(a) Thermal
`conductivity
`steady-state
`laser heat
`flux
`a hot pressed
`specimen
`as a function
`of temperature.
`(b) Thermal
`conductivity
`of a plasma-sprayed
`coating
`specimen
`as a function
`of test
`time at 1316 °C.
`
`NASA/TM--2001-211122
`
`8
`
`12
`
`

`

`' ' ' I ' ' ' -U_
`
`I
`
`I
`
`! ' '
`
`F
`
`1500
`
`C}
`
`oc
`
`_
`
`-.,1
`O"
`
`"'l
`
`C1
`E
`
`-
`
`1000
`
`500
`
`k
`
`Tsurface
`Tback
`Laser
`
`power
`
`---t--
`
`....
`
`c
`
`BSAS
`
`5.0
`
`4.5
`
`4.0
`
`!E
`
`= :3.5
`
`t-
`O
`
`E :3.0
`
`e,-
`
`2.5
`
`3.5 mm disk specimen
`
`(a)
`
`2.0
`
`0
`
`I,,
`20
`
`1__,,
`40
`
`j,,,
`J,,,
`80
`60
`Time, minutes
`
`i,,,
`100
`
`,
`
`,
`
`J ,
`120
`
`0
`40
`
`5.0
`
`l
`
`'-
`
`'
`
`'
`
`I
`
`I
`
`1
`
`'
`
`'
`
`r
`
`I
`
`I
`
`BSAS
`
`Possible
`
`cracking
`
`--,
`
`\
`
`\\
`
`- " - <3- 0_'_ O'_'-'O0
`
`0
`
`0
`
`0
`
`0
`
`0 0
`
`0
`
`"\
`
`4.5
`
`4.0
`
`._>
`
`= 3.5
`"E}
`
`OO
`
`"_ 3.0
`
`e-
`t--
`
`2.5
`
`(b)
`,
`
`,
`
`2.0
`
`200
`
`,
`
`b
`400
`
`,
`
`,
`
`,
`
`J
`600
`
`I
`800
`Surface
`
`,
`
`,
`
`,
`I
`1000
`temperature,
`
`0
`
`,
`
`0
`
`,
`
`°C
`
`,
`
`,
`
`,
`I
`1200
`
`,
`
`L
`1400
`
`,
`
`,
`
`!
`
`,
`1600
`
`determined
`BSAS specimen
`k of a hot-pressed
`conductivity
`4.--Thermal
`Figure
`conductivity
`of BSAS specimen
`laser
`test
`technique.
`(a) Thermal
`a steady-state
`time during
`a heat-cooling
`cycle. A sudden
`drop
`in conductivity
`test
`function
`of
`of
`is due to possible
`specimen
`cracking.
`(b) Thermal
`conductivity
`during
`heating
`as a function
`of surface
`test
`temperature
`(the dashed
`line indicates
`BSAS specimen
`the average
`ceramic
`thermal
`conductivity).
`
`from
`as a
`
`NASA/TM--2001-211122
`
`9
`
`13
`
`

`

`]
`
`'
`
`'
`
`'
`
`I
`
`l
`
`I
`
`I
`
`'
`
`'
`
`'
`
`I
`
`'
`
`'
`
`'
`
`,,,"
`
`8
`10 f
`
`'
`
`'
`
`,
`
`; C}
`
`_
`
`_1_
`
`/--Mullite
`
`BSAS
`
`i _%_.
`
`-
`
`_,
`
`delan_nation
`
`____
`
`6
`
`4 2
`
`200
`
`400
`
`600
`
`1000
`800
`Surface
`temperature,
`
`°C
`
`1200
`
`1400
`
`1600
`
`BSAS
`of 254 i_m thick, plasma-sprayed
`conductivity
`Figure 5.--Thermal
`and mullite
`coatings
`on superatloy
`substrate
`specimens.
`The coating
`specimens
`were previously
`laser-sintered
`at 1300 °C for 2 hours and
`thermal
`conductivity
`of the coating
`specimens
`were measured
`using a
`heating-cooling
`cycle (the dashed
`lines represent
`estimated
`average
`thermal
`conductivity
`values).
`
`NASA/TM--2001-211122
`
`10
`
`14
`
`

`

`1400
`
`1200
`
`1000
`
`800
`
`600
`
`400
`
`2OO
`
`E
`
`e-
`
`o"
`
`E
`
`0
`5O
`
`(b)
`
`6
`
`_r
`
`5
`
`4
`
`3
`
`2
`
`6_
`03
`rn
`
`O
`
`t-
`O
`
`e-
`l-
`
`Tsurfac e _,
`
`\
`
`/
`
`/
`
`_Tback
`
`•
`
`//
`
`/-- kBSAS
`
`_-- Heat
`
`flux
`
`/
`
`/
`
`/
`
`0
`
`0
`
`10
`
`20
`Time, minutes
`
`30
`
`40
`
`'
`
`1
`
`i
`
`I
`
`'
`
`I
`
`{
`
`BSAS
`thickness
`
`254 p.m
`
`Cooling
`
`3.5
`
`3.0
`
`2.5
`
`2.0
`
`--
`
`1.5
`
`-
`
`1.0
`
`iE
`
`"5
`
`"O
`
`c"o
`o
`
`t-k-
`
`0.5
`
`F
`
`80(
`
`....
`
`....
`
`t
`900
`
`....
`
`I
`1000
`Surface
`
`'
`
`I
`
`i
`1100
`temperature,
`
`....
`
`'
`
`I
`I
`1200
`°C
`
`....
`
`I
`1300
`
`1400
`
`of 254 p.m thick,
`BSAS coating
`plasma-sprayed
`conductivity
`Figure &--Thermal
`as a function
`of BSAS coating
`SiC/SiC
`CMC substrate.
`(a) Thermal
`conductivity
`test
`time during
`a heat-cooling
`cycle.
`The conductivity
`rise is due to the coating
`sintering.
`(b) Thermal
`conductivity
`of BSAS coating
`as a function
`of
`test
`temperature.
`
`on
`of
`
`NASA/TM--2001-211122
`
`11
`
`15
`
`

`

`l
`
`F
`
`'
`
`I
`
`I
`
`'
`
`'
`
`t
`
`'
`
`I
`
`20 wt% BSAS + 80 wt% mullite
`disk specimen
`
`(a)
`
`O00q_
`
`<_.
`
`0
`
`O
`
`6.0
`
`5.0
`
`._ 4.0
`
`_-_>
`
`= 3.0
`"0
`t-
`
`2.0
`
`1.0
`
`O E
`
`r-
`p-
`
`0.0
`200
`
`,
`
`,
`
`,
`
`!
`400
`
`,
`
`,
`
`,
`
`,
`
`,
`
`t
`600
`
`,
`
`,
`
`J ,
`800
`Temperature,
`
`,
`
`1 ,
`,
`1200
`
`,
`
`,
`
`I
`1400
`
`,
`
`,
`
`,
`
`1600
`
`,
`
`,
`
`I
`1000
`°C
`
`3.5
`
`'
`
`1
`
`E
`
`I
`
`'
`
`'
`
`'
`
`t
`
`_
`
`l
`
`30 wt% BSAS + 70 wt% mullite
`disk specimen
`
`(b)
`
`O
`
`O
`
`O
`
`3.0
`
`2.5
`
`._>
`
`= 2.0
`"10
`
`C0
`
`E 1.5
`
`e-
`l'-
`
`1.0
`
`0.5
`
`200
`
`,
`
`,
`
`,
`
`I
`400
`
`,
`
`,
`
`,
`
`,
`
`,
`
`I
`600
`
`,
`
`,
`
`,
`
`I
`800
`Temperature,
`
`,
`
`,
`
`,
`
`I
`1200
`
`,
`
`,
`
`[
`1400
`
`,
`
`,
`
`,
`
`1600
`
`,
`
`,
`
`I
`1000
`°C
`
`conductivity
`7.mThermal
`Figure
`specimens
`as a function
`of
`+ 30 wt% BSAS.
`
`of hot-pressed
`temperature.
`
`test
`
`BSAS and mullite mixture
`wt% BSAS;
`(a) Mullite-20
`
`disk
`(b) Mullite
`
`NASA/TM----2001-211122
`
`12
`
`16
`
`

`

`'
`
`'
`
`I
`
`....
`
`I
`
`'
`
`'
`
`i
`
`'
`
`I
`
`I
`
`....
`
`Mullite + 20 wt% BSAS coating
`thickness
`254 I*m
`
`-_--
`
`Cooling
`
`%_
`
`0 C_
`
`_v
`
`Heating
`
`3.5
`
`,_ 3.0
`
`2.5
`
`_
`.__
`
`t-
`O 2.0
`
`e-
`_-
`
`1.5
`
`1.0
`
`0.5
`
`....
`
`800
`
`....
`
`l
`900
`
`I
`1000
`Surface
`
`....
`
`I
`1100
`temperature,
`
`....
`
`°C
`
`J ....
`1200
`
`....
`
`i
`1300
`
`1400
`
`of 254 p.m thick mullite
`conductivity
`8.mThermal
`Figure
`CMC substrate
`SiC/SiC
`as a function
`of
`test
`temperature.
`increase
`was observed
`during
`the heating/cooling
`cycle
`
`+ 20 wt% BSAS coating
`Thermal
`conductivity
`due to ceramic
`sintering.
`
`on
`
`NASA/TM--2001-211122
`
`13
`
`17
`
`

`

`3.5 __ ....
`
`_ '
`
`E BSAS + (mullite
`
`total
`
`thickness
`
`I
`
`+ 20 wt% BSAS)
`254 ixm
`
`(a)
`
`3.0
`
`2.5
`
`,
`E
`_
`
`1 st cycle
`
`\, _ _._'
`
`_\_i _,\ :_;;_.--:._ \
`
`i_._ _:_\<_
`
`_._._ _.
`
`--_
`
`Cooling
`
`-
`
`_
`
`_
`
`_
`
`HA_tinn
`
`g 2.0
`
`"O
`
`EO
`
`E 1.5
`
`e'-
`F-
`
`1.o
`
`0.5 L ....
`800
`
`_ ,
`
`,
`
`I
`900
`
`....
`
`I
`,
`1000
`Surface
`
`....
`
`I
`1100
`temperature.
`
`....
`
`I
`1200
`°C
`
`1 .....
`1300
`
`1400
`
`3.5
`
`....
`
`I
`
`....
`
`I
`
`....
`
`I
`
`....
`
`I
`
`....
`
`I
`
`....
`
`BSAS + (mullite
`
`+ 20 wt% BSAS)
`
`total
`
`thickness
`
`254 i_m
`
`(b)
`
`2nd cycle
`
`.
`....L
`_._!': L\i';t":::_
`
`_
`
`" ii
`
`_':
`
`--_
`..... :C,,
`
`_
`
`:
`
`Cooling
`',? -
`
`_:_,,:
`
`........
`
`Heating
`
`3.0
`
`2.5
`
`!E
`
`"6
`"_ 2.0
`
`1.5
`
`1.0
`
`EOI
`
`3 E
`
`¢-
`F-
`
`0.5
`
`tlZl
`
`8OO
`
`_ ,
`
`,
`
`I
`900
`
`,
`
`,
`
`I
`,
`1000
`Surface
`
`,
`
`....
`
`I
`,
`1100
`temperature,
`
`l
`1200
`°C
`
`,
`
`,
`
`,
`
`I
`,
`1300
`
`,
`
`,
`
`,
`
`,
`
`1400
`
`+ 20 wt% BSAS
`of BSAS (127 l_m thick)/mullite
`Figure g._Thermal
`conductivity
`(127 _m thick) on SiC/SiC CMC substrate
`as a function
`of coating
`test
`temper-
`ature.
`(a) The first heating-cooling
`cycle showed
`a larger conductivity
`increase
`due to ceramic
`sintering.
`(b) The second
`heating-cooling
`cycle had much less
`conductivity
`increase
`probably
`because most of the sintering and densification
`occurred
`during the first cycle.
`
`NASA/TM--2001-211122
`
`14
`
`18
`
`

`

`1600
`
`1400
`
`1200
`
`0
`
`lOOO
`E
`
`8OO
`
`600
`
`(a)
`
`\
`
`\
`
`_-- koverall ceramic
`
`coating
`
`10
`
`20
`
`30
`Time, minutes
`
`40
`
`50
`
`60
`
`ZrO2-8 wt% Y203
`
`_ Mullite
`
`Si
`
`(b)
`
`3.0
`
`2.5
`
`2.0
`
`._>
`
`"o
`(.-
`
`oo
`
`e.-
`I--
`
`1.5
`
`1.0
`
`0
`
`1600
`
`1550 [
`
`1500
`
`9
`
`1450
`
`1400
`
`-
`
`_1_,_;_
`
`_ii )1":::_:t- :2
`
`Q)tn
`E
`
`1350
`
`1300
`
`1250
`
`-
`
`-
`
`-
`
`1200
`
`,
`
`0.0
`
`0.5
`
`Pass-thru
`
`heat
`
`flux 115 W/cm 2
`
`1.0
`Distance
`
`2.0
`1.5
`from surface, mm
`
`2.5
`
`3.5
`
`(2541_m)/
`of a ZrO2-8 wt% Y203 (1371_m)/mullite
`conductivity
`10._Thermal
`Figure
`Si
`(76 _m) on a SiC/SiC
`CMC substrate.
`(a) Thermal
`conductivity
`increased
`during
`a short
`time
`high temperature
`exposure.
`(b) The estimated
`temperature
`distribution
`in the coating
`system.
`
`NASA/TM--2001-211122
`
`15
`
`19
`
`

`

`REPORT
`
`DOCUMENTATION
`
`PAGE
`
`Form Approved
`OMB No. 0704-0188
`
`Public reporting
`burden
`gathering
`and maintaining
`collection of
`information,
`Davis Highway,
`Suite
`
`1 hour per response,
`is estimated to average
`information
`of
`for this collection
`and completing
`and reviewing
`the collection
`of
`information,
`the data needed,
`for
`reducing
`this burden,
`to Washington
`Headquarters
`including
`suggestions
`1204. Arlington,
`VA 22202-4302,
`and to the Office
`of Management
`and Budget,
`
`data sources.
`existing
`searching
`instructions,
`reviewing
`the time for
`including
`aspect of
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`Send comments
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`or any other
`Services, Directorate
`for
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`1215 Jefferson
`Paperwork Reduction
`Project
`(0704-0188), Washington.
`DC 20503.
`
`1. AGENCY
`
`USE ONLY
`
`(Leave
`
`blank)
`
`2.
`
`REPORT
`
`DATE
`
`3. REPORT
`
`TYPE
`
`4.
`
`TITLE
`
`AND
`
`SUBTITLE
`
`September
`
`2001
`
`Thermal
`
`Conductivity
`
`of Ceramic
`
`Thermal
`
`Barrier
`
`and Environmental
`
`Barrier
`
`Coating Materials
`
`6. AUTHOR(S)
`
`Dongming
`
`Zhu, Narottam
`
`E Bansal,
`
`Kang N. Lee,
`
`and Robert A. Miller
`
`AND DATES
`Technical
`
`COVERED
`Memorandum
`
`5. FUNDING
`
`NUMBERS
`
`%_-71_0_20_0
`
`7.
`
`PERFORMING
`
`ORGANIZATION
`
`NAME(S)
`
`AND
`
`ADDRESS(ES)
`
`Aeronautics
`National
`John H. Glenn
`Research
`
`and Space Administration
`Center
`at Lewis
`Field
`
`Cleveland,
`
`Ohio
`
`44135-3191
`
`9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
`
`Aeronautics
`
`and Space Administration
`
`8.
`
`PERFORMING
`
`ORGANIZATION
`
`REPORTNUMBER
`
`E-12971
`
`10.
`
`SPONSORING/MONITORING
`AGENCY
`REPORTNUMBER
`
`National
`
`Washington,
`
`DC 20546-0001
`
`11.
`
`SUPPLEMENTARY
`
`NOTES
`
`NASA TM--2001-211122
`
`Zhu, Ohio Aerospace
`Dongming
`Miller, NASA Glenn Research
`
`Institute, 22800 Cedar Point Road, Brook Park, Ohio 44142; Narottam P. Bansal
`Center: Kang N. Lee, Cleveland
`State University,
`1983 E. 24th Street, Cleveland,
`
`and Robert A.
`Ohio 44115-2403.
`
`Responsible
`
`person, Narottam E Bansal,
`
`organization
`
`code 5130, 216-433-3855.
`
`12a.
`
`DISTRIBUTION/AVAILABILITY
`
`STATEMENT
`
`12b.
`
`DISTRIBUTION
`
`CODE
`
`Unclassified-
`
`Unlimited
`
`Subject
`
`Category:
`
`27
`
`Distribution:
`
`Nonstandard
`
`Available
`
`electronically
`
`at hun://_ltrs.urc.nasa.uov/GLTRS
`
`from the NASA Center
`is available
`This publication
`13. ABSTRACT (Maximum 200 words)
`
`for AeroSpace
`
`Information,
`
`301-621-0390.
`
`Thermal
`
`barrier
`
`and
`
`environmental
`
`barrier
`
`coatings
`
`(TBC's
`
`and EBC's)
`
`have
`
`been
`
`developed
`
`to protect
`
`metallic
`
`Si-based
`
`ceramic
`
`components
`
`in gas
`
`turbine
`
`engines
`
`from high
`
`temperature
`
`attack.
`
`Zirconia-yttria
`
`based
`
`oxides
`
`and
`
`and
`
`8 (BSAS)/mullite
`(Ba,Sr)AI2Si20
`ity values
`of zirconia-yttria-
`
`silicates
`based
`and BSAS/mullite-based
`
`have
`
`as the
`used
`been
`coating materials
`
`coating
`were
`
`materials.
`determined
`
`In this
`at high
`
`thermal
`study,
`temperatures
`
`conductiv-
`using
`a
`
`steady-state
`
`laser
`
`heat
`
`flux technique.
`
`During
`
`the
`
`laser
`
`conductivity
`
`test,
`
`the
`
`specimen
`
`surface
`
`was
`
`heated
`
`by delivering
`
`uniformly
`
`distributed
`
`heat
`
`flux
`
`from a high
`
`power
`
`laser. One-dimensional
`
`steady-state
`
`heating
`
`was
`
`achieved
`
`by using
`
`thin
`
`specimen
`disk
`temperature
`
`configuration
`gradient
`across
`
`and the appropriate
`(25.4 mm diam and 2 to 4 mm thickness)
`the
`specimen
`thickness
`was
`carefully
`measured
`by two
`surface
`
`The
`air-cooling.
`backside
`and backside
`pyrometers.
`
`The
`
`thermal
`
`conductivity
`
`values
`
`were
`
`thus
`
`determined
`
`as a function
`
`of
`
`temperature
`
`based
`
`on the
`
`1-D heat
`
`transfer
`
`equation.
`
`the materials
`
`were
`
`considered
`
`in the
`
`conductivity
`
`measure-
`
`The
`
`radiation
`
`heat
`
`loss
`
`and laser
`
`absorption
`
`corrections
`
`of
`
`ments.
`
`The
`
`effects
`
`of specimen
`
`porosity
`
`and
`
`sintering
`
`on measured
`
`conductivity
`
`values
`
`were
`
`also
`
`evaluated.
`
`14.
`
`SUBJECT
`
`TERMS
`
`Ceramic
`
`coatings;
`
`Thermal
`
`conductivity;
`
`Mullite;
`
`Zirconia;
`
`Celsian
`
`15. NUMBER
`
`OF PAGES
`
`16.
`
`PRICE
`
`CODE
`
`21
`
`17.
`
`CLASSIFICATION
`SECURITY
`OF REPORT
`
`18.
`
`SECURITY
`OF THIS
`
`CLASSIFICATION
`PAGE
`
`Unclassified
`
`NSN 7540-01-280-5500
`
`Unclassified
`
`19.
`
`SECURITY
`
`CLASSIFICATION
`
`20.
`
`LIMITATION
`
`OF ABSTRACT
`
`OF ABSTRACT
`
`Unclassified
`
`Standard
`
`Form
`
`298
`
`(Rev.
`
`2-89)
`
`Prescribed
`298-102
`
`by ANSI
`
`Std. Z39-18
`
`20
`
`