玻璃外文文献加手工翻译_精品文档.doc
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玻璃外文文献加手工翻译_精品文档.doc
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Microstructureandsolidparticleerosionofcarbonbasedmaterialsusedfortheprotectionofhighlyporouscarbon-carboncompositethermal
insulation
R.I.BAXTER,R.D.RAWLINGS
DepartmentofMaterials,ImperialCollegeofScience,TechnologyandMedicine,
LondonSW72BP,UK
Multiparticleerosiontestswereperformedoncandidatecoating(colloidalgraphitepaints)andcladding(densecarbonc—arboncompositesandgraphitefoil)materialsemployedtoprotectporouscarbon—carboncompositethermalinsulationinvacuumandinert-gasfurnacesthatutilizeinertgasquenching.ThedependenceoftheerosionrateontheangleofincidenceoftheerodentwasexaminedandrelatedtothemicrostructureandthemechanismsofmaterialremovalasobservedbySEM.Inaddition,theeffectofathinchemicalvapourdeposited(CVD)carbonlayerontopofacolloidalgraphitepaintcoatingandagraphitefoilcladwasinvestigated.Thecoatingandcladdingmaterialsdisplayedagreatererosionresistanceatallanglesofincidencecomparedtotheporouscarbon—carboncomposite.Ingeneral,thegreatesterosionratewasfoundatanangleofincidenceof90°,wheretheerodentstreamisperpendiculartotheerosionsurface,andbrittlefracturewasthepredominantmechanismofmaterialremoval.Theexceptionwasthegraphitefoilmaterialwhichdisplayedmaximumerosionatanangleofincidenceof60°.Forthismaterial,twomechanismswereeffective:
disruptionofthegraphiteflakes,whichare
mainlyheldtogetherbymechanicallocking,andaploughing-likemechanism.TheadditionofathinCVDcarbonlayertocolloidalgraphitepaintimprovedperformance,whereastheerosionresistanceofthegraphitefoilwasslightlydegradedasthe
CVDlayerwastoothintopreventtheploughing-likemechanism.
1.Introduction
Aclassofhighlyporouscarbon—carbon(C—C)composites,withlowdensitiesintherange0.1—0.4Mgm\3,areutilizedasthermalinsulationinvacuumandinert-gasfurnacesattemperaturesupto2800°C.Aconsequenceofthevacuum-mouldingprocessusedintheproductionofthecompositeisthatthediscontinuousfibresareorientatedintolayerstoformatwo-dimensionalplanarrandomstructure.Thevastmajorityofthevolumeofthecompositeconsistsofinterconnectedporesandthefibrenetworkisbondedattheintersectionsoffibresbydiscreteregionsofthecarbonmatrixasopposedtoacontinuousmatrix.Forthisreasonthesecompositesarealsoknownascarbonbondedcarbonfibre(CBCF).Asaresultofthehighporosityandthefibreorientation,thethermalconductivityperpendiculartothefibrelayerplanesislow,atypicalvalueforamaterialwithanominaldensityof0.20Mgm\3is0.24Wm\1K\1at2000°Cinvacuum.Investigationsintothemicrostructure[3,4],mechanicalproperties[2,5—9]andthermalproperties[10,11]ofthesematerialshavebeenreported.(1997Chapman&HallCBCFisusedinfurnacesemployedinhightechnologyapplicationssuchassingle-crystalgrowing(forexample,siliconorgalliumarsenide)ormetalheattreatment.Theheattreatmentofmetals,suchastoolsteels,isincreasinglycarriedoutinfurnacesthatutilizegasquenching(typicallynitrogenisused)[12,13].Thegasquenchmaybeusedtoreducetheturnaroundtimeofbatchprocessesorasanintegralpartoftheheat-treatmentregime.Theadvantageofgasquenchingduringheattreatment,asopposedtoanoilquench,isthatthecoolingratecanbecontrolled;therefore,itispossibletoreducewarpingandcrackinginthecomponent.Duringgasquenching,parti-culatemattermaybecomeentrainedinthegasflows,andimpingementwiththeinsulationmayresultinmaterialremoval.Inthechallengingenvironmentofgasquenching,thereisarequirementforerosionprotectionoftheCBCFbytheuseofhigherdensitycarbon-basedcoatingandcladdingmaterials.Generally,ductileandbrittlematerialsexhibitdifferenterosioncharacteristics;ofparticularinterestistheirrelationshipbetweentheerosionrateandtheangleofincidence[15].Ductilematerialstendtodisplaymaximumerosionatglancinganglesofimpact,approximately30°formetals,andmaterialremovalisthoughttooccurbyamicromachiningmechanismwithacontributionofdeformationwearathigherangles.Ontheotherhand,forbrittlematerials,maximumerosionisfoundwheretheerodentstreamisperpendiculartotheerosionsurface,andmaterialremovaltypicallyresultsfromtheformationofHertzianorlateralcracks.Althoughitisaconvenientapproachtoidealizematerialserosionbehaviourinthismanner,itisanoversimplification,becaus
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