NASA/TM-- 1999-208812

Advances in Thin Film Thermocouple

Durability Under High Temperature

and Pressure Testing Conditions

Lisa C. Martin and Gustave C. Fralick

Lewis Research Center, Cleveland, Ohio

Keith F. Taylor

Cortez III Service Corporation, Cleveland, Ohio

January 1999

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NASA/TM-- 1999-208812

Advances in Thin Film Thermocouple

Durability Under High Temperature

and Pressure Testing Conditions

Lisa C. Martin and Gustave C. Fralick

Lewis Research Center, Cleveland, Ohio

Keith F. Taylor

Cortez III Service Corporation, Cleveland, Ohio

National Aeronautics and

Space Administration

Lewis Research Center

January 1999

NASA Center for Aerospace Information7121 Standard Drive

Hanover, MD 21076Price Code: A03

Available from

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Springfield, VA 22100Price Code: A03

ADVANCES IN THIN FILM THERMOCOUPLE DURABILITY UNDER

HIGH TEMPERATURE AND PRESSURE TESTING CONDITIONS

Lisa C. Martin and Gustave C. Fralick

National Aeronautics and Space AdministrationLewis Research Center

Cleveland, Ohio 44135

and

Keith F. Taylor

Cortez III Service CorporationLewis Research Center

Cleveland, Ohio 44135

SUMMARY

Thin film thermocouples for measuring material surface temperature have been previously demonstrated on

several material systems and in various hostile test environments. A well-developed thin film fabrication procedure

utilizing shadow masking for patterning the sensors elements had produced thin films with sufficient durability for

applications in high temperature and pressure environments that exist in air-breathing and hydrogen-fueled burner

rig and engine test facilities. However, while shadow masking had been a reliable method for specimens with flat

and gently curved surfaces, it had not been consistently reliable for use on test components with sharp contours. This

work reports on the feasibility of utilizing photolithography processing for patterning thin film thermocouples.

Because this patterning process required changes in the thin film deposition process from that developed for shadow

masking, the effect of these changes on thin film adherence during burner rig testing was evaluated. In addition to

the results of changing the patterning method, the effects on thin film adherence of other processes used in the thin

film fabrication procedure is also presented.

INTRODUCTION

The continuous development and evaluation of both space and aeronautics propulsion systems requires surface

temperature measurement techniques that are reliable and durable in the hostile test conditions typically encountered

in burner rig and test engine environments. Reliable surface temperature data enables experimental verification of

analytical techniques that have been created to determine surface temperature distribution. Such information is rel-

evant to several research areas, including materials and structures evaluation, and fluid mechanics.

Ideally, a surface temperature measurement device that is used in burner rig or engine tests should not disturb

the conditions at the surface during testing. Wire sensors mounted on the test surface may significantly disrupt the

flow conditions. This can be overcome by installing the sensors in machined grooves in the test structure; however,

the heat transfer and temperature distribution profiles may be compromised. In addition, this procedure can alter the

structural integrity of the test component which is often unacceptable in burner rig and test engine situations.

Thin film thermocouples are intended to minimize the negative effects of placing a sensor on the surface of a

test structure. These sensors do not require that the surface be machined and are many orders of magnitude thinner

than wire sensors. As a result, thin film thermocouples add negligible mass to the surface and create minimal distur-

bance of the gas flow over the surface.

At NASA Lewis Research Center, thin film thermocouples were initially developed for superalloy turbine blade

applications for air-breathing propulsion systems (ref. 1). The technology has since been extended to other high tem-

perature material systems, including ceramic, intermetallic and ceramic matrix composite systems (refs. 2 to 3).

Additionally, the technology has been demonstrated in hydrogen-fueled test environments (refs. 2 and 4). The test

configurations have ranged from testing sensors on coupons in static furnace conditions to sensors on flat specimens

and complex shaped components in burner rig and engine test environments.

NASA/TM--1999-208812 1

Thesensorsutilizeplatinum-13%rhodium(Pt-13%Rh)versusplatinum(Pt)thermocoupleelements(standardTypeR)forhightemperaturecapabilityandaresputterdepositeddirectlyontothetestspecimenorcomponent.Thinfilmthermocoupleshavetraditionallybeenpatternedusingshadowmaskingtechniquesontestcomponentswithcurvedsurfaces,includingturbinebladesandcombustorliners.However,shadowmaskingwithstenciledstainlesssteelshimstockhasprovencumbersomeandlimitingwheninstrumentingacomponentcontainingsharpcontours.It isdifficulttoclampastiffmetalmasktothesubstratesoastosufficientlymaintainconstantmask-to-surfacecontactacrosstheentirepatternwhichisneededtopreventshadowingofthedepositedmetalfilm.Addition-ally,theheatpresentduringsputterdepositioncandistortthemaskleadingtoshadowingofthedepositedfilm.Ifseveralthermocoupleelementsarestenciledinthemetalmask,decreasedmaskstiffnessresultsmakingit difficulttosufficientlyclampthemaskbetweentheelementstopreventdistortion.Also,asfinerlinewidthsareneededforsmallerthermocouples,themaskthicknessmustbedecreasedtopreventshadowingfromthepatternedgeline.Be-causethinnermasksarelessstiff,susceptibilitytoheatdistortionincreases.Anexampleofacomponentwithsharpcontoursistheturbinebladeonwhichtheshoulderseparatingtheairfoilandshankareasprotrudesoutfromthebladesurfaceatasharpangleandpresentslimitedspaceforclampingametalmask.Spaceshuttlemainenginetur-binebladeshavebeenshadowmaskedforthinfilmthermocoupleswithgreatdifficultyoverthisbladearearesultinginlowsuccessrateswhenfabricatingworkingthinfilmsensors(refs.2and4).It ispreferabletohaveanalternativemaskingmethodthatisreliableforuseonthesetypesofchallengingshapes.

Theworkpresentedhereindiscussestheviabilityofusingphotolithographymaskingtechniquestopatternthinfilmthermocouplesforapplicationsinburnerrigandenginetesting.Photolithographyemployspatternedphoto-maskswhichareplacedonthesurfaceafterapplicationofphotoresistandarethenexposedtoultravioletlight.Thecomponentwithapatternedlayerofphotoresistis thendepositedwiththesensormaterial.Becauseexposureoccursatroomtemperatureandthephotomaskisnolongerneededafterpatterningthephotoresist,maskdistortionduringsputterdepositionisnotaconcernasit isformetalmasks.Photomasksalsoofferflexibilityin thatpatternswithfinelinegeometriesareachievable.Thisisvaluableinapplicationswhereseveralthermocouplesareneededinasmallspacewhichdictatesthatthesensorelementwidthsbesmallerthanwhatisreliablyfeasiblewithmetalmasks.Flex-iblephotomaskshavebeenfabricatedwithmylarfilmwhichconformtothecomponentshapetherebymakingthephotolithographyprocessapplicabletocurvedsurfaces(ref.5).

ThefabricationprocedureutilizingshadowmaskingthathadbeendevelopedforthePt-13%RhversusPtthinfilmsensorshasproducedfilmsthatweresuccessfullytestedinvarioustestenvironments.However,thisfilmdepo-sitionprocedurehadtobealteredtoaccommodatethetemperaturelimitsimposedbythematerialsusedinthepho-tolithographyprocess.Theresultantfilmswerethentestedfordurabilityonflatspecimensinahydrogen-fueledrocketenginetestfacility.Thetestfacilitywasalteredtoprovidehighpressureconditionsinaspecimentestcham-ber.Previouslyreportedtestsinthisfacilitylimitedthespecimenstohightemperaturegasexposurewhilemountedintheengineexhaustplane(refs.2and4).Whilethistestwasdesignedforareusablelaunchvehicleapplication,theresultsarerelevanttothinfilmsensorapplicationsforairbreathingpropulsioncomponentsaswell.

Inadditiontoinvestigatingtheeffectonfilmdurabilityofalteringthedepositionparameterstoaccommodatethephotolithographymaskingtechnique,twoadditionalfabricationparameterswerelookedattodetermineif therewasanyinfluenceonfilmdurabilityduringhightemperatureandhighpressuretesting.Theeffectofusingfinepowdergritblastingtopreparethesurfacepriortofilmdepositionwasexaminedtodetermineif it aidedfilmadhe-sionduringtesting.Additionally,twodepositionmethods,sputterdepositionandelectronbeamevaporation,werecomparedtodeterminetheeffect,if any,ofdepositionmethodonthedurabilityandadhesivestrengthofthedepos-itedaluminumoxidelayer.Thefunctionofthislayerwastoelectricallyinsulatethethermocoupleelementsfromtheconductingsubstratematerial.

SENSORFABRICATION

Asshownintheschematicin figure1,thinfilmthermocouplesarecomposedof several layers. The substrates,

2.5 x 12.7 x 0.318 cm (1 x 5 x 0.125 in.), were a nickel-based superalloy, Mar-M 246, which is stock material for

first stage turbine blades used in the high pressure fuel turbopump of the space shuttle main engine. The metal ther-

mocouple elements were electrically insulated from the metal substrate by a layer of aluminum oxide. Several steps

were used to prepare this layer. A 125 Hm (0.005 in.) thick coating of PWA 270 NiCoCrA1Y (12 wt% Co, 18 wt%

Cr, 12 wt% A1, 0.3 wt% Y and balance Ni) was electron beam vapor deposited onto the substrates. The coating was

then glass bead peened to increase its density. Half of the twenty samples were grit blasted with 27 Hm aluminum

NAS A/TM-- 1999 -208812 2

oxidepowderinordertostudytheeffectsonfilmadhesionoflightlyrougheningthecoating.All ofthesampleswerethencleanedinmicrosoapanddeionizedwaterandheattreatedinvacuumat1000°C(1800°F)tofacilitatemigrationofaluminumtothesurface.Thiswasfollowedbyanoxidationheattreatmentinairat1000°C(1800°F)tothermallygrowaluminumoxidewithathicknessontheorderof 1to3_tm.Toformapinhole-free,crack-freeelectricallyinsulatingfilm,anadditionallayerofaluminumoxidewasdepositedontothegrownaluminumoxide.

Fortheremainingprocessingsteps,amatrixoffabricationstepswascreatedinordertodeterminetheeffects,ifany,ofeachprocessonfilmadhesionpropertiesduringtestinginharshconditions(tableI).Foreachsetofsamples,oneprocessingparameterwaschangedwhiletheotherparameterswereheldconstant.Sputterdepositionwasusedtodepositaluminumoxideonhalfofthesamplesandelectronbeamvapordepositionwasusedfortheremainingsamples.Sputterdepositionoccurredinthediodemodeinpureargonatapowerdensityof3.09W/cm2.Thesput-teredaluminumoxidefilmswere-2 to3_tmthick.Fordepositionbytheelectronbeamvapordepositionprocess,asubstrateheaterwasmaintainedat900°C.Theevaporatedfilmswere-4 to5_tmthick.Theelectronbeamvapordepositionprocessofferstheadvantageofbeingamuchfasterprocessthansputterdepositionwithprocesstimesof<1hrversus10to20hrfordepositingfilmsofthesethicknesses.Thesampleswerethenreadytobepatternedforthethermocoupleelementspriortometaldeposition.

PerthematrixintableI,halfofthesampleswerepatternedwith0.025cm(0.010in.)thickstainlesssteelshimstockmasksthathadbeenmachinedwithathermocoupleelementpattern.Themetalmaskswereclampedontothesamplesurfaceandsputterdepositedwitha3to5_tmthickplatinumlayer.Themetalsweresputterdepositedinmagnetronmodeatapowerdensityof2.47W/cm2.Aheaterlocatedatanadjacentsputterstationwasmaintainedat400°C.Forthefirstseveralthousandangstromsofdepositedmetal,oxygen-enhancedsputterdepositionwasusedtoaidfilmadhesiontothealuminumoxidelayer.Themaskinganddepositionprocesswasthenrepeatedfortheplatinum-13%rhodiumelement.

Theremainingsampleswerepatternedviathephotolithographyprocess.Fortheliftofftechnique,positivepho-toresistwasfirstappliedtothesurface.Becausethispatterningwasforthedepositionofrelativelythick(3_tm)metalfilms,thephotoresistlayerwasthicker(-3_tm)thanthattypicallyusedinphotolithographyprocessesforthemicroelectronicsmanufacturingindustry(<1_tm).Subsequentstepsincludedexposuretoultravioletlightofthephotoresistthroughapatternedmaskandprocessingindevelopertoremovetheexposedphotoresist.Someunder-cuttingoccurredatthephotoresistlineedgesthatwouldlaterallowgreatereaseinremovingthephotoresistandoverlyingdepositedmetal.Thespecimenswerethenbakedatlowtemperature(90°C,190°F)toremoveanyremainingmoisturefromthephotoresistlayer.

Theuseofpositivephotoresistforpatterningthethermocoupleelementslimitsthetemperaturetowhichthesamplecanbeexposedduringsputterdeposition.Asaresult,somedepositionparameterswerealteredtopreventoverheatingandsubsequentdamagetothephotoresist.Whenphotoresistisdamagedin thisway,thesolventisunabletoremovethephotoresistandoverlyingmetalfilm.Duringmetaldeposition,thespecimenswerepositionedonacooledsubstrateholdermaintainedat0°C.Platinumwassputterdepositedindiodemodeatapowerdensityof1.10W/cm2.Oxygen-enhancedsputterdepositionwasusedforthefirstseveralthousandangstromsofdepositionandthemetalfilmswere-3 to4_tmthick.Afterdepositionoftheplatinumlayer,thephotoresistandoverlyingmetalwereremovedbysoakinginacetone.Theprocessingstepswerethenrepeatedfortheplatinum-13%rhodiumlayer.

Despitestepstakentopreventoverheatingthephotoresistduringdeposition,thesampleswerenotevenlycooledacrossthesurfaceresultinginsomeareasofphotoresistdamage.Consequently,thesolventwasunabletocompletelyremovethephotoresistfromtheentiresurface.Thiswasevidentbyscatteredmetaldepositsonthesur-faceaswellaspooredgelinesforsomeofthethermocouples.Inseverecases,linesofscatteredmetaldepositscrossedbetweenthetwothermocoupleelementsresultinginshortingbetweentheelements.

Figure2isaphotographofasampleinstrumentedwithathinfilmthermocoupleelementpattern.Theindi-vidualelementlengthandwidthwere10.64cm(4.188in.)and0.159cm(0.063in.),respectively.Thejunctionatwhichthetwoelementsmetwasthesurfacetemperaturemeasurementpointandwas-0.318cm(0.125in.)by0.635cm(0.250in.).Thethermocoupleswerefabricatedwithenlargedleadwirepadstoallowgreatereaseinliningupthebareleadwireswiththethinfilmelementspriortoclampingandinstallationintothetestrig.

Inall,therewereeightgroupsofspecimens,eachrepresentingauniquesetofdepositionparameters(tableI).All ofthespecimenswereannealedfor20hrat1000°C(1800°F).Theleadwireswere75_tm(0.003in.)diameterplatinum-13%rhodiumandplatinumbarewiresthatwereclampedtothefilmspriortoinstallationintherocketlaboratoryfacilityfortesting.

NASA/TM--1999-208812 3

ROCKETLABORATORYTESTFACILITY

Therocketlabfacilityinwhichthespecimensweretestedutilizesagaseoushydrogenandoxygenrocketcom-bustortogeneratehightemperature,highheatflux,hydrogen-oroxygen-richhotgasenvironments(ref.6). Thisfacilityapproximatesthethermalshockconditionsofthespaceshuttlemainengineturbopumps.Gastemperaturesrangingfromabout1000to2700°C(1800to5000°F)areobtainableatcombustionchamberpressuresupto4.1MPa(600psi).Forthesetests,theenginewasoperatedatfuel-richratios(O2:H2massflowrateratioof 1.0)resultingingastemperaturesof-900to1100°C.Unlikeprevioustestsinwhichthesamplesweremountedintheexhaustplaneoftheengine(refs.2and4),thesamplesweremountedinspeciallydesignedhardwarewithinthecombustionchamber.Thisprovidedfortestingthespecimensunderhigherpressureconditionsof-3.4MPa(500psi).Thefacilitywasinstrumentedwithapressuresensorformonitoringthepressureprofilewithinthecom-bustionchamber.Thethinfilmthermocouplejunctionwaslocatedapproximatelyinthecenterofthegasflowwithinthecombustionchamber.Thetestdurationwas3sec/run.Thetestrunswerereducedto3secfrom5secusedinprevioustests(refs.2and4) duetoconcernswithoverheatingofthetestchamberhardware.If afilmwasintactafterone3-sectestrun,it thenunderwentadditionaltestrtms.

Fortheinitialtests,thesamplesweremountedwiththesensorsurfacepositionedparalleltothegasflow.Thosesamplesthatperformedwellundertheseconditionswerethentestedwiththesamplesurfacepositionedata22.5°angleintotheflow.Additionaltestingwasperformedonthesurvivingfilmswiththesamplesurfaceata45° angleintotheflow.Thispositionallowedforgreaterimpactofthecombustiongassesonthethinfilmsensors.Notallofthepreparedsamplesweretestedin thefacility.Thosesamplesthatdidnotgivetemperatureoutputduetoabreakinfilmcontinuitywerenottested.

RESULTSANDDISCUSSION

Thethreefabricationprocessesoutlinedabovewereevaluatedforeffectonfilmdurabilityunderhightempera-tureandhighpressureconditions.Sputteredaluminumoxidefilmsandelectronbeamvapordepositedaluminumoxidefilmsdidnotdemonstrateanyappreciabledifferenceinabilitytoaidtheadhesionofthethermocoupleele-mentstothesubstrateduringtesting.Thisevaluationwasbaseduponcomparingallofthesamplesthatwerepro-cessedwithsputtereddepositedaluminumoxidewiththosethathadelectron-beamvapordepositedaluminumoxide.Approximatelythesamepercentageofeachsetofsampleshadintactfilmsaftertesting.Thesamplesthathadbeengritblastedpriortothinfilmprocessingdemonstratedgreaterdurabilitythanthosesamplesthathadbeenleftasis.Theformersetofsampleshadabout50percentwithintactfilmsversusonly20percentwithintactfilmsforthelatterset.ThelightrougheningoftheNiCoCrA1YsurfacemayhaveallowedforsomedegreeofmechanicalinterlockingbetweenthedepositedaluminumoxideinsulatinglayerandtheunderlyingNiCoCrA1Yandthermallygrownaluminumoxidelayers.

Severalsamplespatternedwiththephotolithographyprocessperformedverywellduringtesting.A setofthreesampleswhichhadprocessingproceduresthatincludedgritblastingtheNiCoCrA1Ycoating,sputterdepositionofaluminumoxide,andthephotolithographymasksurvivedallofthetestrunsintherocketlabprocess(samplegroupno.4in tableI).A totalofsixtestrunseachwereconductedontwoofthesamplesandthethirdunderwentthreetestruns.Thesamplepositionsvariedbetweentestrunsandincludedorientationsof0,22.5,and45° anglestothegasflow.All ofthefilmswereintactattheconclusionofthetests.Whilethefocusofthesetestswasfilmadhesionanddurability,temperaturedatawerealsocollected.Figure3includessurfacetemperatureandpressuredatameas-uredinthecombustionchamberduringonetestrun.Thesamplewasorientedata0° angletothegasflow.Thethinfilmthermocouplemeasuredamaximumsurfacetemperatureofapproximately580°C(1080°F)priortoshutdown.Thenominalchamberpressurewas-3.5MPa(510psi).Becausethetestrtmwasfor3seconly,it isexpectedthatthesurfacetemperaturewouldnotapproachthegastemperature,thereforethemeasuredsurfacetemperatureisreasonable.Theapparenttemperaturespikein thedataaftershutdownwaspresentinthedatafromallofthetestrunsandis likelyduetosometypeofelectricalinterferenceintheinstrumentationsystem.Withsubsequenttestruns,themaximumsurfacetemperatureoutputdiddemonstrategradualdegradation,evenasthesampleswereori-entedtowardstheflow.Thismaybeattributabletogradualerosionofthethinfilmmaterialduringeachadditionaltestrunthusaffectingthesensoraccuracy.Thiseffectcanbedelayedwiththeapplicationofaprotectivealuminumoxideovercoatfilmflinthasbeenutilizedinpreviouswork(refs.2and4).

NASA/TM--1999-208812 4

Becausetraditionalwirethermocoupleshaveprovenunabletowithstandthetestconditionsinthisfacility,nogastemperaturedatacouldbecollectedsimultaneouslytoverifythethinfilmthermocoupledata.However,thefactthatthetemperatureprofilein figure3correspondstothechamberpressureprofileindicatesthatthethinfilmther-mocoupleswereoperatingnormally.Thismarksthefirsttimethattemperatureswithinthecombustionchambercouldbemeasuredin thisfacility.

Whilethefilmspatternedwithphotolithographyperformedwellinthesetests,improvementsarestillneededtomakethisareliable,repeatableprocess.Inordertopreventpotentialshortingacrossthethermocoupleelementsduetostraymetaldepositsoutsidetheelementspattern,theprocessforremovingthephotoresistafterdepositionmustbeimproved.Moreconsistentcoolingacrossthespecimenduringsputterdepositionisneeded.Additionally,othersolventssuchascommercialstripperscanbeinvestigatedthatmayremoveheat-damagedphotoresistmoreeasilywithoutcausingdamagetothedepositedmetalfilms.Finally,increasingthethicknessofthephotoresistlayerrela-tivetothatofthemetalfilmmayalsoincreaseeaseofphotoresistremoval.

Sincethemetaldepositionparametersusedforthespecimenspatternedwithphotolithographyproducedfilmsdurableforapplicationsinburnerrigandenginetesting,itwouldbeofinteresttodetermineif thesesameparam-eterscoupledwithmetalshadowmaskswouldalsoprovidedurablefilms.Ofparticularinterestistheeffectofsub-stratecoolingduringsputterdepositiononthefilmadherencesincepastworkhaddemonstratedtheeffectivenessofsubstrateheatinginforminghighlyadherentfilms.It isexpectedthatsubstratecoolingwouldeffectivelyeliminatethemetalmaskdistortionthatoccurswithsubstrateheatingandthehigherpowerdensitiesusedfortheshadowmaskedspecimens.Thisshouldthenreducetheoccurrenceoffilmshadowingoutsideofthepatternedthermocoupleelements.Additionally,thinnermetalmaskscouldthenbeusedformultiplethermocouplesandsmallerlinewidths.If filmsfabricatedwiththesedepositionparametersprovedtobeconsistentlydurablewhenusedwitheithershadowmaskingorphotolithography,thiswouldallowtheflexibilityofutilizingeitherpatterningmethodasneededforanyparticularapplication.Additionalsensorfabricationandtestingisrequiredtodeterminethedurabilityandreliabilityofsuchfilms.

CONCLUSIONS

Thepreliminaryworkdescribedhereindemonstratedthatreplacingthe shadow mask procedure with a photoli-

thography mask procedure is a viable means for patterning thin film thermocouples to be used in high temperature,

high pressure burner rig tests. Films fabricated with deposition procedures designed to accommodate the low tem-

perature requirements for using photoresist proved to be durable in a harsh test environment. While a possible

method for patterning thin film sensors on complex shaped components, improvements are needed to make photoli-

thography a reliable, repeatable process. In particular, the process for removing the photoresist after deposition must

be improved. The deposition process used for photolithography may also have potential for use with shadow mask-

ing. Additional work is needed to determine the viability of using the low temperature deposition process for both

photolithography and shadow masking techniques. The effect of fine powder grit blasting in improving thin film

adherence was also demonstrated. A comparison of deposition methods for aluminum oxide did not yield a clear

advantage of either sputter deposition or electron beam vapor deposition in improving film adherence. Finally, these

tests with thin film thermocouples marked the first time in which surface temperature was measured within the com-

bustion chamber of this rocket lab test facility. Previous use of wire sensors had proven unreliable and insufficientlydurable to withstand the harsh environmental conditions.

REFERENCES

1. Grant, H.P., Przybyszewski, J.S., and Claing, R.G.: "Turbine Blade Temperature Measurements Using Thin

Film Temperature Sensors," PWA-5604-31, Pratt and Whitney Aircraft, NASA Contract NAS3-20831,

NASA CR-165201, 1981.

2. Martin, L.C., and Holanda, R.L.: "Applications of Thin Film Thermocouples for Surface Temperature Measure-

ment," SPIE/NASA Conference on Spin-Off Technologies for Commercial Sensors and Scientific

Instrumentation, San Diego, CA, July 1994.

NASA/TM-- 1999-208812 5

3. Martin,L.C.,andWill,H.A.:"ThinFilmThermocoupleApplicationsinBurnerRigTestingofCeramicMatrixCompositeHardware,"HITEMPReview1997:AdvancedHighTemperatureEngineMaterialsTechnologyProgram,NASACP-10192,1997.

4. Martin,L.C.:"TestingofThinFilmThermocouplesinRocketEngineEnvironments,"AdvancedEarth-to-OrbitPropulsionTechnology,NASACP-3282,1994.

5. Will,H.A.,andBhatt,H.:"StatusofThinFilmHeatFluxSensors,"AdvancedEarth-to-OrbitPropulsionTechnology,NASACP-3282,1994.

6. Green,J.M.:"A VersatileRocketEngineHotGasFacility,"AIAAAerospaceGroundTestingConference,AIAA-94-2487,1994.

TABLE I._ABRICATION PROCESSES FOR TEST SAMPLES

Sanlple Nunlber of

group samplesnumber

1 2

2 3

3 2

4 3

5 3

6 2

7 2

8 3

Thernlocouple

patterningtechnique

Grit blast prepm'ation A1203 deposition

process

Shadow masking None Sputter deposition

Photolithography None Sputter deposition

Shadow nlasking 27 pin A1203 powder Sputter deposition

Photolithography 27 pin A1203 powder Sputter deposition

Shadow nlasking None E beam vapor

Photolithography None E beam vapor

Shadow nlasking 27 pin A1203 powder E beam vapor

Photolithography 27 pin A1203 powder E beam vapor

NAS A/TM-- 1999 -208812 6

Thermocouple Elements 3-5gin

Deposited AI203 2-5gin

Thermally grown AI203 1-2

:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

iiiiiiiiiiNii_i_CirAil_ii_ialii iiii_i2iSi_i_iiiiiiiiii:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Figure 1.--Schematic of thin film

thermocouple layers.

Figure 2.--Test sample instrumented with thin film thermocouple.

NASA/TM-- 1999-208812 7

{530

0r_E

900

800

700

6OO

500

400

300

2OO

100

- 1O0

Thin Film Thermocouple

Chamber Pressure

1 2 3 4 5 6 7 8

Time, seconds

Figure 3.--Temperature and pressure data from thin film thermocouple burner rig test.

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

ulul

m

NAS A/TM-- 1999-208812 8

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January 1999 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Advances in Thin Film Thermocouple Durability Under High Temperature and

Pressure Testing Conditions

6. AUTHOR(S)

Lisa C. Martin, Gustave C. Fralick, and Keith F. Taylor

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135- 3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546- 0001

WU-537-04-22-00

8. PERFORMING ORGANIZATION

REPORTNUMBER

E-11407

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--1999-208812

11. SUPPLEMENTARY NOTES

Lisa C. Martin and Gustave C. Fralick, NASA Lewis Research Center; Keith F. Taylor, Cortez III Service Corporation,

Cleveland, Ohio 44135. Responsible person, Lisa C. Martin, organization code 5510, (216) 433-6468.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Categories: 35, 07, and 20 Distribution: Nonstandard

This publication is available from the NASA Center for AeroSpace Information, (301) 6214)390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Thin film thermocouples for measuring material surface temperature have been previously demonstrated on several

material systems and in various hostile test environments. A well-developed thin film fabrication procedure utilizing

shadow masking for patterning the sensors elements had produced thin films with sufficient durability for applications in

high temperature and pressure environments that exist in air-breathing and hydrogen-fueled burner rig and engine test

facilities. However, while shadow masking had been a reliable method for specimens with flat and gently curved

surfaces, it had not been consistently reliable for use on test components with sharp contours. This work reports on the

feasibility of utilizing photolithography processing for patterning thin film thermocouples. Because this patterning

process required changes in the thin film deposition process from that developed for shadow masking, the effect of these

changes on thin film adherence during burner rig testing was evaluated. In addition to the results of changing the

patterning method, the effects on thin film adherence of other processes used in the thin film fabrication procedure is

also presented.

14. SUBJECT TERMS

Thin films; Thermocouple; High temperature measurements; Hydrogen flame temperature

17. SECURITY CLASSIFICATIONOF REPORT

Unclassified

NSN 7540-01-280-5500

15. NUMBER OF PAGES

]416. PRICE CODE

A0318. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF THIS PAGE OF ABSTRACT

Unclassified Unclassified

Standard Form 298 (Flev. 2-89)Prescribed by ANSI Std. Z39-1B298-102