碳化硅陶瓷基复合材料基体和涂层改性研究进展EI北大核心CSCD

随着航空航天器性能的提高,其热端部件如航空发动机、高超音速飞行器的头锥及翼前缘等服役环境愈加苛刻。为了满足更苛刻的服役环境,需要对碳化硅陶瓷基复合材料(SiC matrix ceramic composites,CMC-Si C)进行基体或涂层改性以发展更长寿命、更耐高温和结构功能一体化的陶瓷基复合材料。介绍了航空航天器热端部件用CMC-SiC复合材料基体和涂层改性的研究进展、成果、现状及存在的问题,指出了今后需要着重解决改性CMC-SiC复合材料的工程化应用问题、发展具有更高使用温度的改性材料体系以及发展在发动机环境中应用的环境屏障涂层体系。     

碳化硅陶瓷基复合材料基体和涂层改性研究进展

随着航空航天器性能的提高,其热端部件如航空发动机、高超音速飞行器的头锥及翼前缘等服役环境愈加苛刻。为了满足更苛刻的服役环境,需要对碳化硅陶瓷基复合材料(SiC matrix ceramic composites,CMC–Si C)进行基体或涂层改性以发展更长寿命、更耐高温和结构功能一体化的陶瓷基复合材料。介绍了航空航天器热端部件用CMC–SiC复合材料基体和涂层改性的研究进展、成果、现状及存在的问题,指出了今后需要着重解决改性CMC–SiC复合材料的工程化应用问题、发展具有更高使用温度的改性材料体系以及发展在发动机环境中应用的环境屏障涂层体系。     

某火箭发动机喷管扩散段烧蚀材料选材

为解决某总体单位提出的某战术导弹火箭发动机喷管扩散段结构及热环境工况要求，进行了扩散段用烧蚀材料试验对比筛选。对短切碳纤维增强酚醛树脂复合材料预浸料和高硅氧玻璃纤维增强酚醛树脂复合材料预浸料进行研究，分析不同材料的拉伸强度、压缩强度、弯曲强度和线烧蚀率，制备产品样件进行水压爆破试验，分析不同纤维长度以及不同纤维种类对产品抗压强度的影响，并通过发动机地面静试研究扩散段烧蚀材料适用情况。结果表明，虽然酚醛树脂/短切碳纤维复合材料的力学性能及耐烧蚀性能均优于酚醛树脂/长丝高硅氧玻璃纤维复合材料，但在发动机温度低于2 000℃、固体粒子含量较多且燃气流速度较大的部位，酚醛树脂/短切碳纤维复合材料的耐冲刷性能较差，无法满足使用要求，酚醛树脂/长丝高硅氧玻璃纤维复合材料耐烧蚀及抗冲刷性能更优异，可满足使用要求。进一步探讨了在特定热、力环境下不同纤维增强体烧蚀材料的热防护机理机制，通过发动机试验进行了选材方案验证，为特定热环境烧蚀材料选用提供了理论及应用依据。     

热障涂层材料研究进展

热障涂层材料广泛应用于发动机热端部件的热防护，能有效提高航空发动机热端 部件的工作温度和使用寿命。目前商用的热障涂层材料为氧化钇部分稳定氧化锆，但其在服役 温度高于 1200?C 时会发生相变而失效，难以满足新一代航空发动机对热障涂层的性能要求。因 此，寻找新型热障涂层材料及其服役性能研究一直是近年来的热点。本文综述了近年来氧化钇 稳定氧化锆、钙钛矿氧化物、烧绿石氧化物以及稀土硅酸盐材料的研究进展，并展望了热障涂 层材料的未来发展趋势。     

材料和结构对柔性热防护材料性能的影响研究

为了对比不同结构与组成的耐高温柔性热防护材料,设计了地面热试验方案,模拟实际使用中的热辐射环境,分别对以高硅氧方格布、高硅氧缝合垫、高硅氧与玄武岩复合缝合垫为主体材料的热防护材料进行隔热性能测试,得到在650℃和900℃热流下保持1800 s时间的试验数据。在本试验工况下,采用高硅氧与玄武岩复合缝合垫为主体材料的热防护材料具有较好的高温隔热性能。通过分析不同材料的隔热性能及其差异产生的原因,试验结果可为今后相关领域的防热设计提供参考。     

航空发动机结构及其关键材料技术分析

提高发动机的性能,进一步降低燃油率,改善经济效益,都须依靠材料技术的进步。航空发动机的服役环境特殊,所以开发耐高温,抗氧化性、导热性与加工性能好的新型材料意义重大。本文重点分析了几种新型材料的性能特点,及新型材料在发动机主要部件的使用情况,展望了未来新材料的发展动态,对提高航空发动机的性能有很大的意义。     

基于材料化学在航天中的应用

对于航空行业来说,航空材料是行业发展的基础。机身的材料和发动机的材料是整个航天器中最重要的结构,因此对于航班的飞行安全与各方面性能起着重要的作用。航空结构材料的特点是强度高,质量轻,可靠性高。飞行器作为一个整体,还需要一些极为精密的材料,这对于材料的发展提出了更高的要求。在这些高质量材料的研发过程中,离不开材料化学,不但可以使得所具备出的材料符合标准要求,还可以降低成本,提高航天器的质量。     

高温结构陶瓷材料的设计准则

针对航空发动机对热结构材料的性能要求，从以下五个方面论述了高温结构陶瓷材料的设计准则，抗氧化性和挥发性，抗蠕变性，显微结构的设计，断裂韧性和抗热震性，抗氧化性和挥发性是由材料的本质特性所决定，脆性是限制结构陶瓷实用的关键，通过对显两重结构和成分的合理设计能有效提高其断裂韧性和抗蠕变性能，而抗热震性则是由构件的材质，结构和环境条件所共同决定的参数。     

烃类热裂解动力学模型研究局限性及对策

通过对目前已有的热裂解制乙烯动力学模型准确度不高、不能适应工业生产原料预测精度要求及深层次原因的剖析,指出了烃类热裂解集总模型和分子模型等应用时不易外推的主要原因是建立这些模型时仅仅依靠原料组成和产物分析的数据,而忽略了复杂自由基反应网络的反应机理研究,而自由基反应规律才是影响模型准确性的最本质因素。提出了分子模拟和工艺过程模拟的理论方法与实验方法相结合的研究思路,并通过将模拟计算数据与文献中的实验或计算数据及已有裂解规律综合进行对比分析的方法。该方法克服了纯实验研究结果误差大、研究进展缓慢的缺点,同时克服理论研究经常与实验数据不符、不易被人接受的缺点,从而较准确、快速地研究烃类热裂解的自由基反应机理。     

固体推进剂热安全性研究进展

综述了近年来固体推进剂热安全性的研究进展,认为固体推进剂发生热爆炸主要是由于推进剂生热速率大于散热速率导致热量累积。影响推进剂热安全性的因素主要由其组成、形状和尺寸等内因,以及贮存环境、老化时间等外部因素构成。固体推进剂热安全性研究多采用分析仪器与实验相结合的方法,借助计算机模拟仿真研究将是今后固体推进剂性能研究的重点。     

Aero-thermo-chemical characterization of ultra-high-temperature ceramics for aerospace applications

Ultra-High-Temperature Ceramic (UHTC) materials, because of their high temperature resistance, are suitable as thermal protection systems for re-entry vehicles or components for space propulsion. Massive UHTC materials are characterized by poor thermal shock resistance, which may be overcome using C or SiC fibers in a UHTC matrix (UHTCMC).The University of Naples “Federico II” has a proven experience in the field of material characterization in high-enthalpy environments. A hypersonic arc-jet facility allows performing tests in simulated atmospheric re-entry conditions. The Aerospace Propulsion Laboratory is employed for testing rocket components in a representative combustion environment. Ad-hoc computational models are developed to characterize the flow field in both facilities and perform thermal analysis of solid samples.Current research programs are related to a new-class of UHTCMC materials, for rocket nozzles and thermal protection systems. The activities include design of the prototypes for the test campaign, numerical simulations and materials characterizations.     

Simulated Environments Testing System for Advanced Ceramic Matrix Composites

The present work aims toward the application of an innovative methodology for testing the environmental performance of advanced ceramic matrix composites in the presence of combined mechanical, thermal, and environmental applied conditions. To obtain a comprehensive understanding of how a composite might perform in certain application environments, a newly developed environmental performance testing platform, which includes simulated equivalent environments system (ES) and a wind tunnel environments system (WS), is proposed. A multiplication factor of 10.8 between the ES and WS at 1300°C has been obtained tentatively.     

Thermal shock behaviors of plasma sprayed YSZ/TiAlCrY system on TiAl alloys

TiAl alloys are promising structural materials in the field of gas turbine engines, due to their low density and high specific strength. Applying thermal barrier coatings (TBCs) is an effective method to increase the service temperature and lifetime of TiAl alloys. In this work, a YSZ/TiAlCrY bilayer system was fabricated by air and vacuum plasma spray techniques on TiAl alloys. The thermal shock behavior was focused on and compared with the traditional YSZ/NiCrAlY system by means of a water-quenching test at 1100 °C. The results show that the YSZ/TiAlCrY system exhibited excellent thermal cycling lifetime with over 210 cycles, which was almost 3 times that of the traditional YSZ/NiCrAlY system on Ni-based superalloys. The failure mechanism was analyzed based on microstructural observations and residual stress calculations. It is found that without the formation of new brittle phases at the interface and suitable CTE were the key factors for the excellent thermal shock resistance of the YSZ/TiAlCrY system on TiAl alloy substrates.     

High-Temperature Testing Techniques for Brittle Refractory Materials

The evaluation of brittle refractory materials calls for special techniques that are different from those normally used for ductile materials. Techniques have been developed at the N.A.C.A. Lewis Flight Propulsion Laboratory to evaluate brittle materials as turbine blades in jet engines and in creep, stress rupture, and thermal shock. The type of equipment and the procedure for creep and stress-rupture testing are described. A parameter is given by which the thermal-shock resistance of brittle materials is related to their physical properties. A simple apparatus has been devised to verify experimentally conclusions given by this parameter. Another apparatus is described that simulates the thermal-shock conditions encountered in a jet engine. The final testing of materials in a jet engine is described.     

Experimental Simulation of the Space Re-Entry Environment for a Carbon/Silicon Carbide Compsite and the Effect on its Properties

An experimental simulation method of space re-entry environment was presented to investigate a carbon/silicon carbide composite and the effect on its properties. The re-entry environment is simulated by controlling the thermal environment and the stress environment. The thermal environment is provided with a high enthalpy combustion chamber with a temperature range of 600°–1800°C and a partial pressure of oxygen of 10–30 kPa. The stress environment can realize both loading and rotating effects with a maximum torque of 150 N·m and a minimum rotation velocity of 32 rpm. Multipurpose testing of a carbon/silicon carbide composite during re-entry can be achieved by this method, such as hot joining, stress-oxidation, creep, and friction behavior.     

Stress effects on the conductivity of particulate beds

Conduction in particulate materials affects a variety of applications ranging from packed bed and multi-phase reactors to calcining/drying kilns, from the storage of bulk reactive or temperature-sensitive materials to material processing. A multi-scale, multi-physics modeling technique—thermal particle dynamics (TPD)—is used to examine heat conduction through static, two-dimensional beds of granular materials. Results of both experiments and a microstructurally based continuum model compare well with those obtained from TPD simulation. The TPD technique, therefore, may provide a unique test-bed for validating or extending theories of effective properties in granular media by yielding detailed mechanical and thermal information not easily measured in experiments. Moreover, in testing this technique it is found that, at low compressive loads or in high aspect ratio beds, the conductivity of particulate materials becomes highly anisotropic. This suggests that it is possible to dynamically tune the granular microstructure and hence the bed's properties.     

Stresses Due to Temperature Gradients in Ceramic-Matrix-Composite Aerospace Components

Ceramic-matrix composites (CMCs) are being considered as replacement materials for divergent flaps and seals in advanced aerospace turbine engines. During service, these components are subjected to severe temperature gradients across the width of the flaps. This paper discusses an analytical procedure to estimate the stresses generated in the CMC flaps due to the temperature gradients. The analytical procedure can be used for a material with nonlinear temperature-dependent stress–strain behavior. This procedure was used to predict the thermal stresses in four candidate CMC systems due to temperature gradients. The thermal stresses along the edges typically exceed the proportional limit, and sometimes the fatigue limit of the CMC.     

Filtration and dust cake experiment by ceramic candle filter in high temperature conditions

Particulate collection at high temperature and high pressure (HTHP) is important in an advanced coal power generation system not only to improve the thermal efficiency of the system, but also to prevent the gas turbine from erosion and to meet the emission limits of the effluent gas. The specifications for particulate collection in those systems such as Integrated Gasification Combined Cycle (IGCC) and Pressurized Fluidized Bed Combustion (PFBC) require absolutely high collection efficiency and reliability. Advanced cyclone, granular bed filter, electrostatic precipitator, and ceramic filter have been developed for particulate collection in the advanced coal power generation system. However, rigid ceramic filters and granular bed filters among them show the best potential. The problems experienced of these systems on performance, materials, and mechanical design were investigated. Ceramic candle filters have the best potential for IGCC at this moment because they have nearly the highest efficiency compared with other filtering systems and have accumulated many reliable design data from many field experiences. The purpose of this study was to investigate the efficiency of ceramic filters and stability of material against high temperature and longterm operation condition by applying fly ash on the surface of the filter and relation of pressure drop and dust cake thickness. Experimental conditions were 50 hours at 450 °C, 650 °C and 850 °C.     

Manufacturing and impact characterization of soy‐based polyurethane pultruded composites

Composites have several advantages such as high corrosion resistance, high strength to weight ratio, and lower maintenance costs over conventional materials. The major cost drivers for composites are raw materials and manufacturing process. Automated manufacturing processes like pultrusion and low cost raw materials can significantly lower the cost of composites. Polyurethane (PU) resin systems are commonly used in the pultrusion industry as they have higher performance characteristics and manufacturing feasibility when compared to conventional resin systems such as polyester and vinyl ester. Manufacturing cost can be further decreased by the use of bio‐based materials such as soy‐based resin systems. In the present work, solid pultruded panels have been manufactured using the base PU and two soy‐based PU resin systems. Pultruded panels were subjected to low velocity impact testing. Soy‐based PU resin systems showed comparable properties to that of the base PU resin system and is a viable alternative to the conventional petroleum‐based PU. POLYM. COMPOS., 35:1070–1077, 2014. © 2013 Society of Plastics Engineers     

High‐Throughput Screening Technology for Automotive Applications

The development of advanced emission control systems to meet the strict regulations requires efficient and flexible material screening capabilities. Here, a high throughput test unit is described. Two case studies demonstrate the rapid screening of relevant parameter spaces and material functionalities which can be used in product development. One involves steady‐state testing of hydrocarbon oxidation in Diesel aftertreatment systems, while the other shows the evaluation of oxygen storage capacity in the optimization of three‐way catalysts for gasoline engines.