Struts are usually adopted in hypersonic engines for efficient fuel injection. Sufficient thermal protection is need for injection struts under extremely high temperature gas scouring environment. The objective of this study is to verify the reliability of the C/SiC-HfB2-HfC composite leading-edge strut under Ma6 engine combustor operation conditions. The heat transfer and ablation behaviors of the strut were investigated numerically and experimentally. The experimental results demonstrated that, under conditions of maximum temperature of similar to 2800 K and maximum transient heat flux of similar to 6 MW/m(2), only minor scouring marks were found at specific locations on the composite leading edge of the strut. Microscopic morphology analysis revealed that the ablation damage to the strut was predominantly concentrated at the leading edge stagnation point, with the maximum ablation depth being approximately 760 mu m. Furthermore, the solid-phase HfO2 produced by the oxidation of ultra-high temperature phases such as HfC and HfB2 can effectively fix the SiO2 in the oxide layer, thereby reducing the ablation rate of the leading edge.

Titanium carbide (TiC) exhibits excellent chemical stability and high electrical conductivity, making it suitable for composites with unique structures and exceptional absorption abilities. In this work, TiO2@TiC composites with varied morphology were synthesized by oxidizing TiC at 400°C, for various durations. With the increase of oxidation time, small white TiO2 particles grew in situ on the surface of TiC particles, ultimately leading to the formation of a continuous structure in which TiO2 covered the surface of the TiC particles. These results indicate that the impedance matching and electromagnetic wave (EMW) absorption properties of TiO2@TiC composites can be modified by adjusting the oxidation time. The minimum reflection loss (RLmin) of the highly oxidized TiO2@TiC composite (TO-4 sample) reached −16.2 dB at a thickness of 2.9 mm. When the thickness was increased from 1.2 mm to 4.7 mm, the composites achieved the broadest effective absorption bandwidth of 13 GHz (from 5 to 18 GHz). These enhanced EMW absorption properties can be ascribed to the presence of defects, pores, heterointerfaces, TiO2, and TiC within the composites, which induce dipole polarization loss, interface polarization loss, and conduction loss. This practical solution provides a method for preparing TiO2@TiC materials with EMW-absorbing properties using oxidation technology.

For high-temperature electromagnetic absorption materials, higher polarization loss is needed to balance the impedance mismatch due to greater conduction loss at elevated temperatures. Here, a SiO2 interface was introduced into a SiCnws/BSAS ceramic based on wide bandgap and low dielectric constant characteristics of SiO2. The interface structure was tailored by changing the SiO2 content. When the SiO2 content reached 15 vol%, three-phase interlaced interfaces were formed, which produced many nano-heterointerfaces that increased the polarization loss by 77.5 %. The optimized SiCnws/SiO2-BSAS ceramic achieved enhanced electromagnetic absorption from 298 K to 873 K, and its effective absorption bandwidth reached 4.1 GHz at 873 K. The elec-tromagnetic absorption mechanism was analyzed from the perspectives of electron transport and space charges. This heterointerface design strategy provides a new method for the development of high-temperature electro-magnetic absorption materials.

Diamond has always been used for reinforcing diamond tools and thermal management materials owing to its high hardness and good thermal conductivity. However, surface inertness of diamond hinders tight bonding with the matrix, leading to significantly declined performance of diamond-reinforced composites. This can be solved by forming coatings with good wetting on diamond surface to serve as a bridge for optimizing interfacial bonding of composites. Accordingly, Mo2C coating was prepared in this study through molten salt method. Key parameters influencing coating quality were investigated systematically by multi-scale microstructural characterizations to shed light on growth mechanism. Results revealed nucleation process of Mo2C highly depended on different diamond surface nucleation sites controlled by reaction mechanism, while further growth of Mo2C coating was controlled by diffusion mechanism. Affinity of as-prepared Mo2C coating on diamond was directly verified by thermal shock tests. Overall, novel insights into nucleation process were provided, promising for further preparation and regulation of carbide coating on diamond.

A polymer-derived ZrC ceramic with excellent electromagnetic interference (EMI) shielding performance was developed to meet ultra-high temperature requirements. The thermal decomposition process of ZrC organic precursor was studied to reveal the evolution of phase composition, microstructure, and EMI shielding performance. Furthermore, the carbothermal reduction reaction occurred at 1300°C, and the transition from ZrO2 to ZrC was completed at 1700°C. With the increase in the annealing temperature, the tetragonal zirconia gradually transformed into monoclinic zirconia, and the transition was completed at the annealing temperature of 1500°C due to the consumption of a large amount of the carbon phase. The average total shielding effectiveness values were 11.63, 22.67, 22.91, 22.81, and 34.73 dB when the polymer-derived ZrC was annealed at 900, 1100, 1300, 1500, and 1700°C, respectively. During the thermal decomposition process, the graphitization degree and phase distribution of free carbon played a dominant role in the shielding performance. The typical core–shell structure composed of carbon and ZrC can be formed at the annealing temperature of 1700°C, which results in excellent shielding performance.

In this paper, the 12k T-700TM Multiaxial-Warp-Knitting–Needle (MWK–N) C/SiC composite and pin were designed and fabricated using the isothermal chemical vapor infiltration (ICVI) method. The composite’s microstructure and mechanical properties were examined by subjection to tensile and interlaminar shear tests. Three types of double-shear tests were conducted for C/SiC pins, including shear loading perpendicularly, along, and at 45° off-axial to the lamination. The fracture surface of the tensile and shear failure specimens was observed under scanning electronic microscope (SEM). The relationships between the composite’s microstructure, mechanical properties, and damage mechanisms were established. The composite’s average tensile strength was σuts = 68.3 MPa and the average interlaminar shear strength was τu = 38.7 MPa. For MWK–N–C/SiC pins, the double-shear strength was τu = 76.5 MPa, 99.7 MPa, and 79.6 MPa for test types I, II, and III, respectively. Compared with MWK–C/SiC pins, the double-shear strength of MWK–N–C/SiC pins all decreased, i.e., 26.7%, 50.8%, and 8% for test types I, II, and III, respectively. The MWK–N–C/SiC composite and pins possessed high interlaminar shear strength and double-shear strength, due to the needled fiber in the thickness direction, low porosity (10–15%), and high composite density (2.0 g/cm3).

Military stealth places higher demands on dual-band electromagnetic wave response in the infrared and microwave bands, and an outer layer with both low infrared emissivity and high microwave transmittance is required for multi-layer compatible stealth materials. In this work, a series of Ti-Si-O films were prepared by magnetron co-sputtering and annealing as the outer layer. The infrared emissivity and microwave transmittance of as-deposited films increase gradually with the decrease of Ti content. After annealing, the microwave transmittance increases obviously due to the occurrence of Ti-O reaction, and only the film with a Ti/Si ratio of similar to 7/1 can maintain a low infrared emissivity. In the optimized film, microwave-transparent TiO grains are generated while original electrically conductive amorphous region still exists and surrounds around TiO, which makes it have both a low average infrared emissivity of 0.32 in infrared band from 2.5 to 25 mu m and a high average transmittance of 88.5% in microwave band (2.42-3.66 cm).

高性能飞行器对涡轮发动机性能需求不断提升,对涡轮转子的耐温性和轻质化提出了苛刻要求.而目前高温合金涡轮转子性能逼近材料极限,难以满足未来涡轮发动机大幅减重提温的需求,先进陶瓷基复合材料(CMCs)涡轮转子成为必然趋势.介绍了涡轮转子用CMCs复合材料的设计、制备、加工、检测,以及各国在CMCs涡轮转子研制方面的进展,研究表明CMCs涡轮转子在液体火箭发动机、先进航空发动机领域具有巨大优势和应用潜力.当前连续纤维增强CMCs复合材料涡轮转子的耐温性能、抗热冲击性能已初步得到验证,而材料强度和韧性不足是制约CMCs在航空发动机涡轮转子上应用的主要因素,发展高强度、高韧性涡轮转子用CMCs材料成为当前研究热点和未来必然趋势.

In this paper, thermal contact resistance (TCR) of three different contacts of a composite are experimentally investigated when the contact interfaces are filled with air. The surface roughnesses of the three contacts are 0.95/16.91 mu m (Contact A, titanium alloy/composite), 9.54/9.73 mu m (Contact B, composite/composite), and 11.53/6.85 mu m (Contact C, composite/titanium alloy). The measured TCRs of the three contacts decrease with an increase in loading pressure and interface temperature. For Contact B, the effect of temperature on thermal contact resistance gradually decreases with an increasing loading pressure. For Contact C when loading pressure increases to 3.6 MPa, the decreasing trend of the thermal contact resistance with increasing loading pressure becomes mild. Additionally, experimental uncertainties are analyzed and calculated.

Shear properties of 2D C/SiC z-pinned joint were aimed to improve through z-pin microstructural features optimization. Results demonstrated that joint shear properties could be effectively improved through z-pin density, diameter and ply orientation adjustment. As 2D C/SiC z-pin density increased by approximately 0.1g/cm3, joint strength increased linearly approximately 18%. As z-pin diameter increased from 3.8mm to 4.0mm, joint strength increased approximately 10.1% and 6.9% from 4.0mm to 4.3mm. When z-pin ply orientation changed from 0/90 to +45/−45, corresponding joint strength increased approximately 10.9%. Shear rupture of 2D C/SiC z-pin was the only failure mode of corresponding joint, whereas the failure was competing result of shear and bending damages in the z-pin. Corresponding strengthening and toughening mechanisms were related to SiC matrix cracking and carbon fiber bridging.

Progressive failure model is developed to investigate shear behaviors of 2D C/SiC z-pinned joint prepared by chemical vapor infiltration (CVI). It includes progressive failure model of 2D C/SiC composites and cohesive model of faying plane, in order to describe joint nonlinear shear behaviors and z-pin shear-off failure mode, respectively. All cohesive parameters are directly obtained from mechanical properties of 2D C/SiC composites. Results show that the model can almost reproduce joint shear behaviors and z-pin shear-off failure process. Joint failure results from coupled fiber tensile and fiber–matrix shearing damages at faying plane. The model also successfully demonstrates that joint shear properties can be effectively improved by changing z-pin density and diameter. The relationship between joint properties and mechanical properties of 2D C/SiC composites are subsequently obtained with the model. In this sense, joint shear strength increases with cohesive or in-plane shear strengths of 2D C/SiC composites.

综述了ZrB2及其复合陶瓷的高温氧化行为,认为ZrB2陶瓷是一种优异的高温结构材料,其氧化失效是由于氧化产物B2O3保护层挥发失效而导致的;二元陶瓷ZrB2-SiC由于SiC的加入,高温抗氧化性能大大提高,并对其在不同温度下的氧化物结构进行了阐述.在此基础上提出了进一步提高ZrB2-SiC陶瓷抗氧化性能和服役温度的方法,并以添加TaC和LaB6形成三元复相陶瓷为例进行了说明.

涡轮转子是燃气涡轮发动机（GTE，gas turbine engine）的核心部件。受到蜘蛛网强韧性和协同承载特性启发，本研究提出构筑蛛网仿生结构（SWS，spider-web-structure）陶瓷复合材料（CMCs）涡轮叶盘的研究思路。本工作通过SWS预制体设计与成型研究，完成SWS-SiC/SiC涡轮叶盘制备，表征了SWS-SiC/SiC涡轮叶盘性能。结果表明：所制备SWS-SiC/SiC涡轮叶盘的破裂转速达到158000 r/min（叶尖线速度达到702.84 m/s），是常规2D-SiC/SiC涡轮叶盘破裂转速的3.09倍，是某GTE涡轮叶盘设计转速（85000 r/min）的1.86倍；经设计转速测试后，所制备SWS-SiC/SiC涡轮叶盘的一阶、二阶、三阶频降分别是：0.41%，0.03%和0.26%。