【作者】 李建章；

【导师】 张立同； 李斗星；

【作者基本信息】 西北工业大学 ， 材料学， 2006， 博士

【摘要】 连续碳纤维增强碳化硅基复合材料（C／SiC）是一种在航空航天与能源领域具有广泛应用价值的战略性轻质热结构材料，具有高比强与不发生灾难性断裂等优异特性，成为高推重比航空发动机热端部件材料的重要候选，有望满足耐高温抗氧化长寿命的目标需求。本文针对高推重比航空发动机热端部件多因素复杂环境，采用光学显微镜（OM）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）与高分辨电子显微镜（HRTEM）等多种分析手段，跨尺度表征了三维编织连续碳纤维增强碳化硅基复合材料（3D C／SiC）在热物理化学模拟条件和应力模拟条件下的微结构演变，围绕微结构演变-性能演变之间的关系，系统研究了3D C／SiC的环境行为演变规律，获得了3D C／SiC的失效机制和微结构控制单元与要素。在此基础上，综合归纳出材料的失效本质，成功地分析了3D C／SiC在各种模拟环境中的失效模式与机理。主要研究内容与结果如下：1．发现“簇”是连续纤维增强陶瓷基复合材料（CFCC）中普遍存在的结构特征，提出“纤维簇”是控制CFCC强韧化的主要结构单元之一。纤维簇与单根纤维、纤维束三者之间的竞争与协同，形成了CFCC的跨尺度微结构控制准则框架，可实现CFCC的最佳强韧化，并成功应用于3D C／SiC的制备、性能控制、力学分析和失效机制中，有效地提高了材料的综合效能。2．首次提出CFCC的“仿生基本结构模型”和“功能失效机制”，详细阐述了其内涵与主要内容，统一了3D C／SiC在各种复杂坏境中的失效机制和失效模型，成功应用于3D C／SiC的失效分析和材料优化设计中。其与跨尺度微结构控制准则一起，成为陶瓷基复合材料新型强韧化理论的主要部分。3．通过对3D C／SiC在不同模拟环境的微结构进行系统观察，特别是从TEM和HRTEM角度深入对大量样品分析，观察到诸多具有普遍性的微观机制和新现象，从而为分析3D C／SiC的环境行为演变与获得失效机制奠定了坚实基础。（1）首次得到C／SiC所特有的典型微观机制—缺口状氧化—的TEM直观证据，完善了国际上有关缺口状反应的模型和认识，分析了缺口状氧化机制的形成过程。该机制属多部位的非均匀氧化，普遍存在于热物理化学介质的环境中，是组元本征氧化性质差异与应力／热物理化学介质在微观尺度交互作用的结果，对3D C／SiC复杂耦合环境的行为有重要影响。（2）TEM观察到700℃下3D C／SiC中的基体和纯水反应生成SiO₂非晶膜，形膜温度低于以往研究中所确定的温度，从而对含水气氛下3D C／SiC环境行为与温度变化之间的关系有了新的理解。（3）提出界面区的概念，完善了对CFCC界面结构和作用的认识，系统研究了C／SiC内界面区与裂纹的相互作用机理及其影响因素，建立起裂纹偏斜和界面脱粘的物理模型，从而推进了对C／SiC增韧机制和力学行为的理解。4．从微结构演变-性能演变之间关系的角度，通过对不同分压纯氧气氛、纯水气氛和纯熔盐、不同分压比含氧耦合气氛下3D C／SiC环境行为的比较研究，建立起3D C／SiC在含氧气氛中的失效综合示意图，同时确定出：（1）氧化温度区间及纯氧气氛下各区间的动力学控制要素。（2）微结构控制性单元和要素—涂层、热历史与含碳组元。（3）热物理化学环境主导因素—氧和盐（Na₂SO₄）以及影响3D C／SiC最为严重的条件—水氧盐耦合环境。（4）含氧气氛中的失效本质—氧（和SO₃）对碳相的损伤破坏。5．从结构的角度，深入分析了3D C／SiC的两大结构特征（即纤维束交叉处（交界孔处）的SiC基体弱约束和应力集中，以及强的弱界面结合）对力学行为的影响。在此基础上，从宏观断口形貌，纤维束、簇和单丝的拔出与断裂特征、裂纹特征、界面区的脱粘和滑移、界面区与各组元结构／织构的变化等多个方面，对不同温度不同应力参数下3D C／SiC单调拉伸、疲劳和蠕变的微结构演变进行了系统观察与比较，确定出微结构控制单元与要素，得出具体的失效机制。讨论了3D C／SiC疲劳与蠕变失效机制的多尺度特性与相互差异，表明两者机理相似，微结构变化特征难以区分，仅在各种机制发生顺序和比例上有所不同。6．基于上述各种模拟环境的失效分析和“仿生结构模型”与“功能失效机制”，确定出分区间的重量变化率是C／SiC环境性能表征最直观和最基本的指标，并用于建立失效判据，分析了3D C／SiC热物理化学介质／应力条件耦合环境中的失效机制并经实验验证。更多还原

【Abstract】 Continuous carbon fiber reinforced silicon carbide matrix composites （C/SiC）were a high-temperature lightweight structural materials which were strategic innational defense and have the potentials in many fields including aerospace, space,and nuclear reactor. C/SiC were non-catastrophic with pseudo-plastic behavior andhad some advantage such as high strength-weight ratio, which made it a key candidateto aim at use with oxidation-protection and long life at high temperature when appliedas hot-section component in aero-engine with high thrust-weight ratio.The complicated multi-factor environments in hot-section component inadvanced aero-engine were selected as objective environment in this dissertation.Multi-scale characterization including optical microscopy （OM）, scanning electronmicroscopy （SEM）, transmission electron microscopy （TEM） and high resolutiontransmission electron microscopy （HRTEM） were made use to investigatemicrostructural evolving of 3-dimensional C/SiC （3D C/SiC） served in thermo-physical and chemical simulated atmosphere and simulated stress condition. Therelationship between the multi-scale structural change and properties change, and thecorresponding response to environment in 3D C/SiC were systematically explored, sothe failure behavior were clearly understood and microstructural controlling unit andelement were obtained. These failure and microstructure investigate induced theessential failure model and mechanism which were used to predict and analysis thefailure behavior in environments much more complicated. The prediction fitted wellwith experimental phenomena. The main results are as follows:1. "Fiber cluster" were first proposed to be a main kind of structural unit tocontrol strength and toughness of continuous fiber-reinforced ceramic composite（CFCC）. The competition among fiber cluster, single fiber and fiber yarn formed themulti-scale microstructural control criterion which was successfully applied inprocessing, improving properties, mechanical behavior and failure mechanism for 3DC/SiC and which made the performance of C/SiC used in this thesis improved largely. 2. Biomimetic "basic structural model" and "function failure mechanism" ofCFCC were first proposed and introduced to 3D C/SiC, which were successfullyapplied in failure analysis and materials design and optimization. The definition anddetailed content of biomimetic "basic structural model" and "function failuremechanism" were given. The biomimetic model and mechanism became a simplifiedand unified model and mechanism for in-service analysis of 3D C/SiC in allcomplicated simulated environments and became a main part of new strengtheningand toughening theory of ceramic matrix composites.3. The microstructure of 3D C/SiC in different simulated environments weresystematically studied, especially in TEM and HRTEM. Many microscopicmechanism and new phenomena were observed directly and statistically whichformed some bases for analysis of environmental behavior evolving.（1） Notch-like oxidation mechanism of C/SiC was first observed in TEM andthen were modified in understanding and model. The form mechanism of notch-likeoxidation mechanism was discussed in detail. This mechanism occurred frequently inthe environment with high temperature chemical medium and influenced heavily thebehavior of 3D C/SiC.（2） SiO₂ amorphous films were found in TEM in 3D C/SiC served in H₂O at700℃, which corrected the react temperature between SiC and H₂O and led to newunderstanding of the relationship between environmental behavior and temperaturechange for 3D C/SiC in H₂O-containing atmosphere.（3） Interfacial zone were defined. The interactions of the interfacial zone withcracks were systematically investigated whose physical models were established,which advanced the understanding in toughening mechanism and mechanicalbehavior of C/SiC.4. Considering the relationship between microstructure evolving and propertiesevolving, the environment behavior of 3D C/SiC in pure oxygen with different partialpressure, pure water, pure molten salt, and O₂-containing coupled atmosphere withdifferent partial pressure were comparatively studied and the failure map of 3D C/SiCin O₂-containing atmosphere. Also below were obtained: （1） The oxidation temperature zone and kinetics determining factor in pure O₂.（2） The microstructural controlling unit and element—coating, heat history andcarbonaceous constituent.（3） The dominant factor in thermo- physical and chemical environment—oxygenand salt （Na₂SO₄）. H₂O-O₂-Na₂SO₄ coupled environment became the most severeservice condition for 3D C/SiC.（4） The failure essence of 3D C/SiC in O₂-containing atmosphere—the attack ofoxygen （and SO₃） upon carbonaceous constituent.5. From structure, the effects of two structural characteristic of 3D C/SiC onmechanical behavior, which were weak restrict of SiC matrix at the crossover pore orcrossover between fiber yarns and strong weak-interface bond, were analysis detailed.Based these two structural characteristic, the monotonic tensile behavior, fatiguemechanism and creep behavior of 3D C/SiC under different parameter and variedtemperature were systematically investigated and compared from many aspectsincluding macroscopic fractograph, pull-out and fracture characteristic of single fiber,fiber cluster and yarn, crack characteristic, debonding and sliding in interfacial zone,and texture/structure change of interfacial zone and constituents. The microstructuralcontrolling unit and element and corresponding failure mechanism were obtained. Thefatigue failure and creep failure were both multi-scale and the difference betweenthem were discussed. They were similar in mechanism and microstructuralcharacteristics, and different only in order and proportion of every type.6. Based on the failure analysis and biomimetic model and mechanism discusseddetailed above, it was established that relative weight change in different temperaturezone was the most direct and basic characterization parameter of C/SiC in serviceenvironments. The biomimetic model and mechanism also were used to predict thefailure behavior of 3D C/SiC when in the coupled environments between stressconditions and themo- physical and chemical conditions, and the prediction resultswere accordant with experiments.更多还原