sitionare℃,ahydrogentoMTSratioof,andapressureofafewkPa.Argonwasusedasdilutegastoslowdownthechemicalreactionrateofdeposition.Afterthedensificationofthecompositeswasfinished,theC/SiCcompositeswerecoatedwithsilicon-molybdenumalloy(Si-Mo)meltattemperatureof~℃invacuumfor.h...OxidationtestsTheoxidationtestswereconductedat~℃inair.Thethermalshockexperimentswereconductedasfollows:thesampleswereplacedintothefinthedevelopmentofasuccessfuloxidationprotectionsystemforcarbon-basedcompositematerials[,].Thecriticalfactorsforoxidationprotectionsystemofcarbon-basedcompositematerialsare:(i)oxygendiffusionthroughthecoatingmicro-cracks；(ii)volatilityofcoatingmaterialsathightemperature；(iii)oxidationofcoatingbydiffusionofoxygenthroughthecoatinglayer,and；(iv)thechemicalandmechanicalcompatibilitybetweencoatingandsubstrate.Theoxidationprotectioncoatingforcompositesisusuallypreparedbychemicalvapordeposition(CVD)methodwhichhasbeendescribedelsewhere[].Thecoatinghasasandwichstructurewhichcouldbedividedintothreelayers.TheinnerlayerisCVDSiClayer,themediumlayerisboron-containinglayer(BNorBC),andtheouterisCVDSiClayer.Athightemperatures,BO-SiOglassisformedfromtheoxidationofboron-containinglayerandSiCandsealseasilythemicro-crackstoprotectthecomposites[,].Theservicetemperatureofthiskindcoatingislowerthan℃becausetheborateglassesexhibithighvaporpressureathightemperature.Inordertoimprovetheservicetemperatureofoxidationprotectioncoating,itisnecessarytodevelopnewkindofcoatingmaterialssystem.Thispaperisacontinuationofanarticlespublishedpreviously[-],andtheaimsare(i)developanewkindofoxidationprotectioncoatingforC/SiCcompositeswhichcouldbeutilizedabove℃；(ii)investigatetheoxidationbehaviorofcoatedC/SiCcomposites,and；(iii)examinetheeffectsofoxidationonthemechanicalpropertiesandfailurebehaviorofthecomposites..Experimentalprocedure..Preparationofthreedimensionalcarbon/siliconcarbidecompositesPAN-basedcarbonfiberwasemployedandeachyarncontainedfilaments.Thefabricpreformwaspreparedbythreedimensionalbraidedmethod,andsuppliedbyNanjingInstituteofGlassFiber(PeopleRepublicofChina).Thefibervolumefractionwas.Inthepresentexperiment,isothermal/isobaricchemicalvaporinfiltration(ICVI)wasemployedtoprepareC/SiCcompositewhichhasbeendescribedelsewhereindetails[-].InICVIprocess,athinlayerofpyrolyticcarbonwaspre-depositedonthesurfaceofcarbonfiberasinterfaciallayerwithbutaneat℃priortodensification.Methytrichosilane(MTS,CHSiCl)wasusedfordepositionofSiCandwascarriedbybubblinghydrogenintothereactionchamber.Typicalconditionsbeingusedfordepositionare℃,ahydrogentoMTSratioof,andapressureofafewkPa.Argonwasusedasdilutegastoslowdownthechemicalreactionrateofdeposition.Afterthedensificationofthecompositeswasfinished,theC/SiCcompositeswerecoatedwithsilicon-molybdenumalloy(Si-Mo)meltattemperatureof~℃invacuumfor.h...OxidationtestsTheoxidationtestswereconductedat~℃inair.Thethermalshockexperimentswereconductedasfollows:thesampleswereplacedintothef加。氧化行为三维C/SiC复合材料和二维C/SiC复合材料氧化过程相似可以图C/SiC复合材料中SiC基体微裂纹SEM图：CVI制备SiC基体氧化曲线由Lamouroux[]提出模型得到证明。众所周知，碳纤维、和CVI制备SiC基体热膨胀系数有明显差异。T碳纤维是一种各向异性材料，通过两个CTE表征：一个径向CTE（-.-.-℃-）和一个纵向CTE(.-℃-).CVI制备SiC基体CTE是.-℃-[]。因此,在SiC基体上有许多由于热应力产生垂直于纤维轴微裂纹(Fig.)。在温度为~℃氧化过程,这些微裂纹扮演了一个供氧内扩散通道。在这一阶段,氧化机理被认为是由碳与氧之间化学反应控制,氧化率应遵循阿伦尼乌斯方程。很明显,温度增加导致氧化速率加快。随着温度增加到~℃,裂纹宽度(e(T)）变窄，这个温度称为功能温度。TTeTe()e是在室温下裂纹宽度,T是测试温度,T是裂纹宽度为零时温度。菲克鲁生定律认为裂纹宽度减少会引起氧化机理变化[、]。因此,复合材料氧化机理受氧气在微裂纹中扩散控制。氧扩散受微裂纹几何形状影响，特别是有关微裂纹宽度和深度。在温度高于℃时,微裂纹宽度由于SiC基体热膨胀变得非常狭窄，SiC氧化变得明显，并受氧通过SiC层扩散控制。此外，大量氧化SiC最终会覆盖微裂纹。因此，氧化机理受氧在SiC层扩散控制。在图中，CVI制备SiC基体氧化过程,验证了复合材料氧化模型。在℃以下，SiC基体氧化重量基本没有变化。在~℃温度范围内、氧化速率随着温度升高而迅速提高。.C/SiC复合材料氧化保护涂层结构表征一个重要问题是有关氧气主要障碍选择。它通常是强调形成原位吸附氧可吸附在复合材料自由表面上。硅基陶瓷拥有最好热膨胀相容性且具有最低氧（a）（b）（c）图涂层C/SiC复合材料氧化图氧化保护层孔洞和抗弯强度关系曲线化速率。因此，它们经常被用于碳基复合材料保护。据报道,一定量薄无定形二氧化硅有低氧扩散系数，可通过加入其他氧化物控制玻璃粘度来改善。如图所示,扫描电镜观察结果表明，氧化保护涂层包括三层：()最外层是玻璃态二氧化硅氧化层；()中间层是Si＋MoSi层；()内层是SiC层。由于Si＋MoSi层氧化，玻璃态二氧化硅层氧化层非常光滑。在Si＋MoSi层，MoSi颗粒分散在硅基体中。如图b、c、d所示为中间层TEM形貌和衍射图形。进一步观察用TEM观察玻璃态二氧化硅颗粒显示该层主要由二氧化硅和少量钼元素组成(图)。硅、二硅化钼氧化反应反应式如下[，]：SiOOSi()SiOMoOOMoSi()MoO有相对低熔点(℃)和优越流动性,以致它能密封氧化涂层裂纹，提高复合材料抗氧化性。通常，Mo是一种玻璃网络中调节元素，并不能单独形成玻璃。但在SiO存在条件下，Mo和SiO能形式一种具有结晶和氧扩散能力高阻抗玻璃。在玻璃系统中，钼以MoO形式存在[]。.氧化作用对含涂层复合材料力学性能影响研究发现，含涂层C/SiC复合材料在整个氧化过程中氧化增重。在最初氧化阶段、氧化增重和温度之间呈现线性关系。当氧化时间超过小时时增长速率减少。氧化时间达到小时时，氧化重量达到最大值,然后随着氧化时间增加而降低。与之相对应，在小时氧化时间内，抗弯强度稍有降低。然后，在小时后，抗弯强度急剧降低,当氧化时间达到小时时，抗弯曲度为零(图)。显然，氧化增重曲线最大值点是涂层C/SiC复合材料力学性能减弱起点。氧化增重在初始阶段归因于Si和MoSi氧化反应，通过和两个化学反应完成。然而，产物MoO由于高温时拥有高蒸汽压而很容易逃离氧化涂层。因此，氧化增重率随温度而减小。随着硅氧化进行，Si和MoSi含量减少，如果Si和MoSi在小范围内存在，氧化将生成SiC。由于局部氧分压低，SiC氧化活性将改变[]。如果局部压力达到临界值，气态产物将会逃溢对SiO-MoO玻璃层造成伤害。氧化涂层中形成孔洞变成了氧传输通道(图)。进而,加速氧化过程,导致C界面层和碳纤维氧化。最重要是孔洞形成部位是氧化涂层失效点。图所示为热冲击（℃～℃）对抗弯强度影响。随着热冲击次数增加,抗弯强度稍有下降。在次热冲击后，抗弯强度保持在MPa，但涂层C/SiC复合材料失效行为与复合材料相似(图)。研究结果表明:涂层C/SiC复合材料具有优越抗热震性。结论、研发了一种可用于三维碳纤维增强SiC复合材料新型Si-MoSi氧化保护涂层。该氧化保护涂层有三层结构：外层是氧化硅玻璃层，中间层是Si-MoSi层，内层是SiC层。、研究了涂层C/SiC复合材料在~℃温度范围内氧化性。整个氧化过程可分为三个阶段：()℃℃，SiC氧化变得明显，受O通过SiC层扩散控制。、被包覆C/SiC复合材料表现出了优越抗氧化性和抗热震性。复合材料分别于空气中℃退火h和℃~℃间热冲击次后，抗弯强度分别保持了和。氧化重量变化和抗弯强度之间关系，表明了氧化保护涂料关键是氧化涂层增重最大点就是失效开始点。致谢本研究工作由国家自然科学基金会(NNSF、国家航空科学基金会(NASF)和国家国防科学基金会(NDSF)支持。inthedevelopmentofasuccessfuloxidationprotectionsystemforcarbon-basedcompositematerials[,].Thecriticalfactorsforoxidationprotectionsystemofcarbon-basedcompositematerialsare:(i)oxygendiffusionthroughthecoatingmicro-cracks；(ii)volatilityofcoatingmaterialsathightemperature；(iii)oxidationofcoatingbydiffusionofoxygenthroughthecoatinglayer,and；(iv)thechemicalandmechanicalcompatibilitybetweencoatingandsu附录外语文献原文英文原文OxidationbehaviorandmechanicalpropertiesofC/SiCcompositeswithSi-MoSioxidationprotectioncoatingYONGDONGXU,LAIFEICHENG,LITONGZHANG,HONGFENGYING,WANCHENGZHOUStateKeyLaboratoryofSolidificationProcessing,NorthwesternPolytechnicalUniversity,Xi’an,Shaanxi,People’sRepublicofChinaAnewkindofoxidationprotectioncoatingofSi-MoSiwasdevelopedforthreedimensionalcarbonfiberreinforcedsiliconcarbidecompositeswhichcouldbeservicedupto℃.Theoveralloxidationbehaviorcouldbedividedintothreestages:(i)℃℃,theoxidationofSiCbecamesignificantandwascontrolledbyoxygendiffusionthroughtheSiClayer.Microstructuralanalysisrevealedthattheoxidationprotectioncoatinghadathree-layerstructure:theoutlayerisoxidationlayerofsilicaglass,themedialayerisSiCMoSilayer,andtheinsidelayerisSiClayer.ThecoatedC/SiCcompositesexhibitedexcellentoxidationresistanceandthermalshockresistance.Afterthecompositesannealedat℃forhinairand℃~℃thermalshockfortimes,theflexuralstrengthwasmaintainedbyandrespectively.Therelationshipbetweenoxidationweightchangeandflexuralstrengthrevealedthecriteriaforprotectioncoatingwasthatthemaximumpointofoxidationweightgainwasthefailurestartingpointforoxidationprotectioncoating..IntroductionCarbonfiberreinforcedsiliconcarbidecomposite(C/SiC)isakindofpromisingthermalstructurecompositesforuseinapplicationsrequiringhighstrength,lowdensity,andhighfracturetoughnessatelevatedtemperaturesinaero-enginesandaerospace[].However,asevereproblemisthatthecarbonfiberandin-terfaciallayerofthecompositeareeasytobeattackedbyoxygeninairatthetemperaturesaslowas℃[,].Themainreasonisthattherearemanymicrocracksonthesiliconcarbidematrixresultedfromthemis-matchofthermalexpansioncoefficientsbetweencarbonfiberandsiliconcarbidematrix.Theoxidationhasasignificanteffectontheweakeningandmechanicalpropertiesofthematerials.Ithasbeenreportedthattheoxidationweightlossofwtresultedinthetensilestrengthdecreaseofalmostatmediumtemperatureof℃byoxidationtreatment[].Sofar,twokindsofapproacheshavebeendevelopedtoprotectthecarbonfiberandinterfaciallayer.Thefirstapproachisoxidationprotectionofinterfaciallayer,suchcomposition-gradedC(B)interfaceandBNinterfaciallayer[-].Obviously,theeffectofthisapproachislimitedbecausetheinterfaciallayerisusuallyverythin(~nm).Thesecondapproachisoxidationprotectioncoatingforcomposite,andisconsideredasapromisingmethod.Therearemanyissueswhichmustbeconsideredinthedevelopmentofasuccessfuloxidationprotectionsystemforcarbon-basedcompositematerials[,].Thecriticalfactorsforoxidationprotectionsystemofcarbon-basedcompositematerialsare:(i)oxygendiffusionthroughthecoatingmicro-cracks；(ii)volatilityofcoatingmaterialsathightemperature；(iii)oxidationofcoatingbydiffusionofoxygenthroughthecoatinglayer,and；(iv)thechemicalandmechanicalcompatibilitybetweencoatingandsubstrate.Theoxidationprotectioncoatingforcompositesisusuallypreparedbychemicalvapordeposition(CVD)methodwhichhasbeendescribedelsewhere[].Thecoatinghasasandwichstructurewhichcouldbedividedintothreelayers.TheinnerlayerisCVDSiClayer,themediumlayerisboron-containinglayer(BNorBC),andtheouterisCVDSiClayer.Athightemperatures,BO-SiOglassisformedfromtheoxidationofboron-containinglayerandSiCandsealseasilythemicro-crackstoprotectthecomposites[,].Theservicetemperatureofthiskindcoatingislowerthan℃becausetheborateglassesexhibithighvaporpressureathightemperature.Inordertoimprovetheservicetemperatureofoxidationprotectioncoating,itisnecessarytodevelopnewkindofcoatingmaterialssystem.Thispaperisacontinuationofanarticlespublishedpreviously[-],andtheaimsare(i)developanewkindofoxidationprotectioncoatingforC/SiCcompositeswhichcouldbeutilizedabove℃；(ii)investigatetheoxidationbehaviorofcoatedC/SiCcomposites,and；(iii)examinetheeffectsofoxidationonthemechanicalpropertiesandfailurebehaviorofthecomposites..Experimentalprocedure..Preparationofthreedimensionalcarbon/siliconcarbidecompositesPAN-basedcarbonfiberwasemployedandeachyarncontainedfilaments.Thefabricpreformwaspreparedbythreedimensionalbraidedmethod,andsuppliedbyNanjingInstituteofGlassFiber(PeopleRepublicofChina).Thefiberv        附录外语文献原文英文原文OxidationbehaviorandmechanicalpropertiesofC/SiCcompositeswithSi-MoSi2oxidationprotectioncoatingYONGDONGXU,LAIFEICHENG,LITONGZHANG,HONGFENGYING,WANCHENGZHOUStateKeyLaboratoryofSolidificationProcessing,NorthwesternPolytechnicalUniversity,Xi’an,Shaanxi710072,People’sRepublicofChinaAnewkindofoxidationprotectioncoatingofSi-MoSi2wasdevelopedfort

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