Cf/SiC复合材料抗氧化涂层的制备、性能与保护机理

用化学气相沉积法(chemical vapor deposit,CVD)在碳纤维增强碳化硅复合材料(carbon fiber reinforced silicon carbide composites,Cf／SiC)表面制备了CVD—SiC粘接层、自愈合功能层和CVD—SiC耐冲蚀层组成的3层涂层体系,并进行了氧化实验。结果表明：单层CVD—SiC涂层保护试样的氧化质量损失速率比无涂层试样的明显降低,含有自愈合层的3层涂层保护试样比单层CVD—SiC保护试样的氧化质量损失速率又有明显降低。3层涂层保护的试样800～1300℃的氧化质量损失率非常小,氧化288h后仍能保持较高的弯曲强度。通过扫描电镜观察到自愈合层的玻璃态物质进入涂层裂纹中,有效地填充裂纹并阻挡氧的通过。同时,因涂层不均产生的孔洞或玻璃态物质流失后产生的涂层裂纹等缺陷会导致其自愈合功能的失效,使Cf／SiC复合材料不均匀氧化。     

水热温度对SiC-C/C复合材料表面水热电泳沉积SiCn-MoSi2复合抗氧化涂层的影响

采用水热电泳沉积法在SiC–C/C复合材料表面制备了纳米碳化硅和二硅化钼的复相(SiCn–MoSi2)抗氧化涂层。采用X射线衍射和扫描电子显微镜等对制备涂层的晶相组成、表面及断面微观结构进行了表征。研究了水热温度对制备涂层的结构及高温抗氧化性能的影响,分析了涂层在1 600℃静态氧化行为及失效机理。结果表明:外涂层主要由MoSi2和β-SiC晶相组成。复相外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高。SiCn–MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1 600℃氧化80 h后氧化质量损失为3.6×10–3 g/cm2。复合涂层在1 600℃的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层中出现贯穿性的裂纹和孔洞导致的。     

水热温度对SiC–C/C复合材料表面水热电泳沉积SiCn–MoSi2复合抗氧化涂层的影响

采用水热电泳沉积法在SiC–C/C复合材料表面制备了纳米碳化硅和二硅化钼的复相(SiCn–MoSi2)抗氧化涂层。采用X射线衍射和扫描电子显微镜等对制备涂层的晶相组成、表面及断面微观结构进行了表征。研究了水热温度对制备涂层的结构及高温抗氧化性能的影响,分析了涂层在1 600℃静态氧化行为及失效机理。结果表明:外涂层主要由MoSi2和β-SiC晶相组成。复相外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高。SiCn–MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1 600℃氧化80 h后氧化质量损失为3.6×10–3 g/cm2。复合涂层在1 600℃的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层中出现贯穿性的裂纹和孔洞导致的。     

C/SiC复合材料表面化学气相沉积涂覆SiC涂层及其抗氧化性能

采用化学气相沉积法,在1 100 ℃,在碳纤维增强碳化硅复合材料表面制备SiC涂层,研究了涂层连续沉积和分4次沉积(每次沉积时间为6 h)所制备的SiC涂层的微观结构和涂层样品的氧化性能.结果表明:两种SiC涂层的厚度均约为40 μm,且4次沉积制备的SiC涂层为一个连续的整体.涂层连续沉积时,表面只出现裸露裂纹;分4次沉积制备时,表面出现大量边缘有SiC生长锥的附着裂纹,附着裂纹在高温氧化时易发生自愈合.与连续涂层样品相比,4次涂层能显著提高C/SiC样品的抗氧化性能.4次涂层样品经1 400 ℃,50 h氧化后,质量损失为0.88%,质量损失速率稳定在6.30 × 10-5 g/(cm2?h),且4次涂层样品具有优异的抗热震性能.     

基体改性对SiC/SiC复合材料高温抗氧化性能的影响

采用先驱体浸渍-裂解工艺结合三种基体改性方式制备了SiC/SiC复合材料,通过形貌分析和力学性能测试,分析了基体改性对Si C/SiC复合材料高温抗氧化性能的影响。研究表明,经1200℃静态空气氧化100h后,三种基体改性的复合材料弯曲强度几乎没有下降,氧化200h后,弯曲强度保留率均可达到80%;氧化300h后,复合材料内部结构没有氧化现象,表面区域界面层的氧化程度降低。改性基体中的B元素氧化生成液相封填SiC涂层表面,延缓了SiC涂层的氧化进程,并阻止氧化介质进入复合材料内部,保护纤维和界面层,从而使SiC/SiC复合材料的长时静态高温抗氧化性能明显提高。     

包埋法制备碳/碳复合材料碳化硅涂层缺陷的形成机制及控制

用包埋法在碳/碳(C/C)复合材料表面制备了碳化硅(SiC)涂层及改性涂层.用扫描电镜观察涂层的微观形貌.从理论上探讨了涂层缺陷的形成机制,分析了改性剂对SiC涂层形貌、晶粒尺寸的影响.结果表明:添加改性剂后,涂层晶粒变小,涂层致密,表面未出现裂纹,断面孔洞的数量减少,尺寸减小.在1 773K的抗氧化性比未添加改性剂涂层的显著提高.     

碳/碳复合材料表面SiC/c-AlPO_4复合涂层及其抗氧化机制

采用二次包埋法和水热电泳沉积法相结合的工艺在碳纤维增强碳复合材料表面制得SiC/方石英型磷酸铝(cristobalite aluminum phosphate,c-AlPO4)复合涂层。借助X射线衍射仪和扫描电镜对复合涂层的晶相组成和显微结构进行了表征。研究了复合涂层的高温氧化性能,讨论了复合涂层氧化、失效的机理。结果表明:复合涂层具有双层结构,包埋的SiC内层主要由α-SiC,β-SiC和少量的游离硅组成,外层由c-AlPO4颗粒构成,内外层结合紧密。复合涂层在1300～1500℃范围内具有良好的抗氧化性能,其氧化激活能为117.2kJ/mol,氧化过程主要受氧在c-AlPO4层中的体扩散速率所控制;氧化气体逸出留下的孔洞是复合涂层防氧化失效的主要原因。     

Cf/SiC 复合材料的 ZrB2-SiC/SiC 超高温陶瓷涂层研究

采用两步包埋法在Cf/SiC复合材料表面制备了Zr B_2-SiC/SiC超高温陶瓷涂层。借助SEM、XRD对涂层的微观结构及物相组成进行了分析研究,并进行了高温静态氧化和热震测试。研究表明,1500°C氧化5 h后,涂层表面覆盖有平整的玻璃相氧化层,氧化失重率为6.4%;热震测试10次后涂层的氧化失重率为14%。Zr B_2-SiC/SiC涂层能有效提高Cf/SiC复合材料的高温抗氧化性能。     

基于因素分析的C/SiC复合材料氧化动力学模拟

用因素分析法对C/SiC复合材料在氧气气氛下的氧化相对质量变化曲线进行了分析,确定了在不同温度区间内影响其相对质量变化的控制因素:在温度θ<700℃时复合材料的氧化速率由碳氧反应控制,属线性机制;随温度的升高,氧气通过涂层微裂纹的扩散将控制复合材料的氧化速率,属抛物线性机制;在温度θ>1000℃时,微裂纹逐步封闭,氧气通过SiO2生成层的扩散以及涂层表面的氧化将分别成为影响复合材料氧化速率的控制因素。在此基础上,建立了描述复合材料氧化过程的动力学模型。     

SiCf/SiC复合材料高温抗氧化研究进展

连续SiC纤维增韧SiC陶瓷基复合材料(SiCf/SiC CMCs)具有低密度、优异的高温力学性能和抗氧化性能,在航空发动机热端部件上具有广阔的应用前景,具备提高发动机推重比和使用温度、减轻无效重量、简化系统结构等显著优势.延长SiCf/SiC复合材料在航空发动机高温氧化环境下的服役寿命是当前需要解决的难题.本文从纤维、界面相、基体、表面涂层四个方面综述了SiCf/SiC复合材料高温抗氧化研究进展.采用多元多层自愈合界面相、对基体进行改性以及采用表面自愈合整体涂层都可以有效提高SiCf/SiC复合材料在高温氧化环境中的使用稳定性和寿命.     

碳化硅冶炼炉逸出气体的组成及理化性质研究

利用自行发明的多热源碳化硅冶炼炉，以煤（或焦炭）和石英砂为原料合成SiC，同时伴生大量副产品可燃性气体，研究了煤种和冶炼工艺对燃气的组成及酸碱性的影响，并对经济效益进行分析。结果表明，燃气中以CO气体为主，平均含量可达70％，CO＋H2平均含量达85％，CO＋H2＋CH4平均含量达90％，使用无烟煤、烟煤焦炭或焙烧料法可提高合成气中CO含量，若燃气用于火力发电可节约25．8％的电费成本。     

Oxidation of Silicon and Silicon Carbide in Ozone-Containing Atmospheres at 973 K

The oxidation behavior of a silicon wafer, chemically vapor-deposited SiC, and single-crystal SiC was investigated in an oxygen—2%–7% ozone gas mixture at 973 K. The thickness of the oxide film that formed during oxidation was measured by ellipsometry. The oxidation rates in the ozone-containing atmosphere were much higher than those in a pure oxygen atmosphere. The parabolic oxidation kinetics were observed for both silicon and SiC. The parabolic rate constants varied linearly with the ozone-gas partial pressure. Inward diffusion of atomic oxygen formed by the dissociation of ozone gas through the SiO₂ film apparently was the rate-controlling process.     

碳化硅晶片的制备技术

碳化硅晶须和晶片都是陶瓷基、金属基、树脂基复合材料的理想增强体，与碳化硅晶须相比，有关碳化硅晶片制备与应用的报道相对较少。论述了碳化硅晶片在复合材料中的应用，比较了国内外碳化硅晶片的各种制备技术。阐明了加热方式对碳化硅晶片制备的影响。指出低成本、新型热源的开发与推广应用有利于实现碳化硅晶片的规模化生产。     

渗硅碳化硅材料的高温氧化

研究了全碳粉反应渗硅碳化硅(PCRBSC)材料,在1300℃静态空气中的高温氧化行为.研究结果表明:PCRBSC材料的氧化过程遵循直线-抛物线规律,其结构对高温氧化有很大的影响,特别是游离硅fsi和游离碳fc的含量对氧化影响更大,fsi含量高的PCRBSC材料单位面积氧化增重(Δm/s)明显,fc含量高的PCRBSC材料氧化后表现为先减重后增重,氧化层断口经扫描电镜观察有明显的气孔存在.     

Preparation of reaction bonded silicon carbide (RBSC) using boron carbide as an alternative source of carbon

RBSC composites are fully dense materials fabricated by infiltration of compacted mixtures of silicon carbide and carbon by molten silicon. Free carbon is usually added in the form of an organic resin that undergoes subsequent pyrolysis. The environmentally unfriendly pyrolysis process and the presence of residual silicon are serious drawbacks of this process. The study describes an alternative approach that minimizes the residual silicon fraction by making use of a multimodal particle size distribution, in order to increase the green density of the preforms prior infiltration. The addition of boron carbide provides an alternative source of carbon, thereby eliminating the need for pyrolized organic compounds. The residual silicon fraction in the RBSC composites, prepared according to the novel processing route, is significantly reduced. Their mechanical properties, in particular the specific flexural strength is by 15% higher than the value reported for RBSC composites prepared by the conventional approach.     

Improved Resistance to Damage of Silicon Carbide-Whisker-Reinforced Silicon Nitride-Matrix Composites by Whisker-Oriented Alignment

The effects of whisker-oriented alignment on resistance to damage of SiC( w )/Si₃N₄ composites have been investigated by the Vickers indentation method and R -curve behavior. It is shown that increasing the degree of whisker-oriented alignment decreases the lengths of Vickers impressions and indentation cracks. The results exhibit rising R -curve behaviors for the SiC( w )/Si₃N₄ composites with different degree of whisker-oriented alignment. Moreover, the initial crack length c _i, the threshold of crack growth resistance K _i, and the upper bound of crack growth resistance K _∞ change regularly with increasing degree of whisker-oriented alignment. All results suggest that the whisker-oriented alignment improves the resistance to damage of the composites, resulting in a more reliable and usable composite.     

连续纤维增韧碳化硅陶瓷基复合材料研究

采用化学气相浸渗法制造了连续碳纤维和碳化硅纤维增韧碳化硅陶瓷基复合材料，并对复合材料的显微结构和力学性能进行了研究，C/SiC／SiC复合材料的密度分别为2．1g/cm^3和2．5g/cm63，在断理解过程中表现出明显的非线性和非灾难性的断裂行为和规律，C／SiC和SiC／SiC弯曲强度分别为450MPa和850MPa，从室温至1600℃强度不发生降低；断裂韧性为20MPa.m^1/2和41．5MPa.m^1/2，断裂功为10kJ.m^-2和28．1kJ.m^-2，冲击韧性为62．0kJ.m^-2和36．0kJ.m^-2，C/SiC和SiC/SiC复合材料具有优异的抗热震性能，经1300℃→←3000℃，50次热震后，强度保持率高达96．4％，热震不是材料性能损伤的控制因素，而SiC/SiC复合材料优异的抗氧化性能，对温度梯度不敏感，得合材料喷管在液体火箭发动机上成功地通过了地面实验。     

Conversion of Oak to Cellular Silicon Carbide Ceramic by Gas-Phase Reaction with Silicon Monoxide

Oak has been converted to a porous biocarbon template by annealing in an inert atmosphere above 800°C. Subsequent infiltration with gaseous SiO at 1550–1600°C under flowing argon of atmospheric pressure finally resulted in the formation of a porous, cellular β-SiC ceramic. The conversion retains the biomorphic cellular morphology of oak tissue. While pores in the cell walls with a diameter less than ∼1 μm vanished, two distinct pore channel maxima representing tracheidal cells and large vessels remained in the SiC ceramic. Depending on the cellular morphology of different kinds of wood, e.g., strut thickness and pore size distribution, gas-phase conversion to single-phase β-SiC can be used to manufacture cellular ceramics with a wide range of pore channel diameters.     

Wetting and interfacial phenomena of Ni‐Ta alloys on CVD‐SiC

When designing high‐temperature brazing processes for ceramic materials, the interfacial phenomena between the liquid media and the adjoining surfaces must be known to design reliable joints. In order to assess the feasibility of using Ta‐containing alloys for high‐temperature brazing of SiC‐based composites, the wetting of molten Ni‐Ta alloys on ultra‐pure chemical vapor deposited (CVD) SiC substrates has been investigated using the sessile drop technique. For all of the compositions and experimental conditions, good wetting was observed with fast spreading. The interfacial behavior is determined by the competition between the typical interfacial phenomena of the pure elements; specifically, either the dissolution of the ceramic phase by Ni or the formation of a new interfacial layer, TaC, by reaction between Ta and CVD‐SiC, which prevails depends on the relative amount of the single element in the alloy.     

新奇的生物材料制碳化物陶瓷工艺

概述了木材等生物材料制碳化硅及其复合材料的工艺。列举了碳化硅晶须，木质碳化硅，碳化硅反射镜，波纹蜂窝及叠层碳化硅陶瓷的制备实例。