SiC含量对C/C-SiC复合材料弯曲强度及抗氧化性能的影响

选用聚碳硅烷（PCS）为前驱体，对密度分别为1．34g／cm^3，1．52g／cm^3和1．62g／cm^3的针刺炭布C／C材料进行液相致密化处理，制得密度达1．75g／cm^3的C／C-SiC复合材料，并与密度为1．85g／cm^3的同结构高密度C／C材料的弯曲强度和抗氧化性能进行了对比分析。结果表明：密度为1．34g／cm^3的C／C材料经过PCS致密化处理，在保持高密度C／C材料的弯曲强度同时，显著提高了材料的抗氧化性能。     

C/C-SiC复合材料的组合工艺制备及基体改性研究进展

C/C-SiC复合材料是一种耐磨性好、抗烧蚀的高温热结构材料,被广泛应用于航空航天、摩擦制动、热防护等领域,然而几种制备C/C-SiC复合材料的单一工艺方法均存在着局限性与不足之处.本文重点介绍了几种制备C/C-SiC复合材料的组合工艺,并分析了组合工艺各自的优缺点.综述了C/C-SiC陶瓷基复合材料基体改性的相关进展...     

先驱体转化法制备C/C-SiC复合材料研究

以多孔C/C复合材料为预制型,聚碳硅烷(PCS)为先驱体,制备了C/C-SiC复合材料。研究了浸渍液浓度和不同C/C复合材料预制体密度等级对C/C-SiC复合材料的密度和力学性能的影响。结果表明:当浸渍液浓度为50%时,复合材料的密度均达到最佳值;不同的预制体密度对制得的复合材料性能有很大的影响,其中初始密度为1.2g/cm3试样制得的复合材料性能达到最优,其密度达到1.786g/cm3,弯曲强度达204.1MPa,剪切强度为16.1MPa,断裂韧性为6.83MPa·m1/2。     

碳/碳复合材料氧化的研究进展

碳/碳(C/C)复合材料因比重轻、导电导热快等优异性能,成为航空航天领域应用的理想材料,但在643K以上温度的含氧环境中,碳/碳(C/C)复合材料易发生氧化而导致失效,因此,研究C/C复合材料的抗氧化性能非常必要。本文对C/C复合材料的氧化过程进行了总结,氧化过程主要是低温段的碳氧化学反应控制和高温段的氧气经边界层与碳反应的扩散控制。目前,针对C/C复合材料的抗氧化性弱的问题,有研究者提出,基体改性和涂层防护是提高材料抗氧化能力的主要方法。本文综述了静态氧化和高温氧化烧蚀的最新研究进展,从相关的研究进展可知,该材料的应用环境较为单一,为此本文基于海洋腐蚀环境,分析了C/C复合材料的氧化过程。     

C／C-SiC复合材料的水润滑摩擦磨损特性研究

本文在MRH-3型环块式磨损试验机上,进行了C／C-SiC与Ni基合金摩擦副的摩擦磨损实验。测定了水润滑状态下,在相同转速,载荷,磨损时间条件下,配对摩擦副的摩擦系数和磨损率。用扫描电子显微镜（SEM）观察了配对摩擦副的磨损表面形貌。初步探讨了C／C-SiC复合材料的摩擦、磨损特性及机理,对C／C-SiC复合材料在水润滑条件下作为摩擦件使用提供了实验依据。     

基于等离子火炬的C/C复合材料烧蚀实验及理论研究

基于等离子火炬进行了C/C复合材料烧蚀实验,获得了材料的烧蚀表面形态及烧蚀产物光谱,确定了等离子火炬务件下的典型烧蚀产物.同时基于JANAF数据,通过最小能量法计算了等离子火炬低压高焓状态的热化学烧蚀产物,与光谱检测结果基本一致.     

C/C复合材料ZrB2-SiC涂层的微观结构及烧蚀性能研究

采用包埋法在密度为1.63g/cm~3的C/C复合材料上制备了不同ZrB_2含量的ZrB_2-SiC复相陶瓷涂层,考察了不同配比包埋粉料对涂层微观结构和抗烧蚀性能的影响。结果表明,当包埋粉料中ZrB_2质量分数为50%时,涂层ZrB_2含量最多,氧乙炔烧蚀60s时,其线烧蚀率、质量烧蚀率最低,分别为5.3×10~(-4) mm/s和2.1×10~(-3)g/s;在烧蚀过程中,SiC氧化产物SiO_2发生了相变,形成玻璃态,吸收大量热量。玻璃态的SiO_2相包裹着ZrO_2相,使得在烧蚀过程中,有效降低了烧蚀火焰冲击对ZrO_2造成的损失,ZrO_2导热系数低,是一种优异的热障材料,从而降低了复合材料烧蚀率。     

C/C-Cu复合材料微观结构及高温耐烧蚀性能研究

为提高C/C复合材料的高温耐烧蚀性能,采用化学气相沉积与高温渗铜工艺制备了密度为2.01 g/cm3的C/C-Cu复合材料.采用高温氧乙炔焰考察了复合材料的高温耐烧蚀性能,并利用X射线衍射仪(XRD)与扫描电子显微镜(SEM)对复合材料烧蚀前后的物相与微观结构进行了表征.结果表明:经20 s的氧乙炔焰烧蚀后,复合材料的...     

C/C-SiC梯度基复合材料氧化行为研究

研究比较了Ｃ／Ｃ－ＳｉＣ梯度基复合材料和Ｃ／Ｃ复合材料的氧化行为．实验结果表明：ＳｉＣ通过占据表面活性点提高了共沉积基体的氧化起始温度;由于减少了碳与氧的接触面积,阻挡氧化凹坑的扩展,降低了材料的氧化质量损失速率．利用ＳＥＭ观察了梯度基复合材料微观氧化过程     

碳/碳复合材料概述

介绍了C/C复合材料的两种致密化工艺:化学气相法,液相浸渍-碳化法及二者复合致密化。重点介绍了C/C复合材料的抗氧化技术:内部抗氧化,抗氧化涂层。针对C/C复合材料的两大应用领域:火箭喉衬材料和刹车材料,简述了通过C/C-Cu和C/C-难熔金属碳化物的制备进一步提高C/C复合材料的耐烧蚀性能以及C/C复合材料的摩擦磨损性能。     

Thermal performance and ablation characteristics of C/C-SiC for thermal protection of hypersonic vehicle

A small-scale plasma ablation facility was employed to test the C/C-SiC composite material for investigating the thermal performance and ablation characteristics under two heat flux conditions, 3593.54 kW·m^?2 and 5644.86 kW·m^?2. The morphology of post-test specimens was analyzed with the ablation rates calculated. The average mass ablation rates of two group specimens were 0.01735 and 0.10620 g·s^?1 respectively with average linear ablation rate of 0.00680 and 0.09407 mm·s^?1. Specimen surface could be divided into three regions with typical layered structure characteristics. For the stagnation point ablation test, the structural deformation in the ablation surface area featured in vertical layering and lateral regionality, forming an ablation pit near the stagnation point. In the center region, sublimation occured primarily, accompanied by a serious jet scouring of the molten liquid phase, as well as a small amount of oxidation reaction; Jet erosion with thermal sublimation was the main factor for the mass loss in the transitional region; Thermochemical reactions were mainly carried out in the marginal region. The SiO₂ generated from the thermochemical reaction of the material filled the interspace well and prevented the thermochemical reaction from penetrating deeper through the crack. The protective layer in the molten state with high viscosity reduced the damage of the high-speed jet impact material.     

Laser ablation resistance and mechanism of Si-Zr alloyed melt infiltrated C/C-SiC composite

Ablation resistance of C/C-SiC composite prepared via Si-Zr alloyed reactive melt infiltration was evaluated using a facile and economical laser ablation method. Linear ablation rates of the composite increased with an increase in laser power densities and decreased with extended ablation time. The C/C-SiC composite prepared via Si-Zr alloyed melt infiltration presented much better ablation resistance compared with the C/SiC composite prepared by polymer infiltration and pyrolysis process. The good ablation resistance of the composite was attributed to the melted ZrC layer formed at the ablation center region. Microstructure and phase composition of different ablated region were investigated by SEM and EDS, and a laser ablation model was finally proposed based on the testing results and microstructure characterization. Laser ablation of the composite experienced three distinct periods. At the very beginning, the laser ablation was dominated by the oxidation process. Then for the second period, the laser ablation was dominated by the evaporation, decomposition and sublimation process. With the further ablation of the composite, chemical stable ZrC was formed on the ablated surface and the laser ablation was synergistically controlled by the scouring away of ZrC melts and evaporation, decomposition and sublimation process.     

Microstructure and ablation properties of La2O3 modified C/C-SiC composites prepared via precursor infiltration pyrolysis

Effects of La₂O₃ modification on the microstructure, mechanical and ablation properties of C/C-SiC composites were investigated. Experimental results show that a new La₁₀(SiO₄)₆O₃ phase was generated during heat treatment process. The presence of the La-compounds, namely La₂O₃ and La₁₀(SiO₄)₆O₃, had an important impact on the structure of reinforced skeleton and the molten oxide film, and thus strongly affected the mechanical and ablation properties of the composites. Excessive La addition induced the structural damage of the reinforced skeleton, resulting in weakened mechanical and ablation properties. The C/C-SiC composites with 25.65 wt.% La₂O₃ addition displayed better mechanical properties and the best ablation resistance. The La₁₀(SiO₄)₆O₃ phase could react with molten silica to form a viscous glass during ablation. The transformation of La-compounds into La₂Si₂O₇ can reduce the ablation of SiO₂ and enhance the glass film, so as to protect the composites from further ablation.     

Electrical properties of C/C and C/C-SiC ceramic fibre composites

The electrical properties of carbon/carbon (C/C) and carbon/carbon-silicon carbide (C/C-SiC) ceramic composites were measured. The results show that the capacitance decreases rapidly with an increase in frequency and it becomes constant above a frequency of 500 kHz, whereas the dissipation factor increases with increasing frequency. C/C-SiC composites give higher value than C/C composites due to the presence of microcracks.     

Influence of h-BN as additive on microstructure and oxidation mechanism of C/C-SiC composite

Due to the favorable self-healing performance, hexagonal boron nitride (h-BN) as additive in the matrix can significantly influence the oxidation behavior and the kinetic characteristics of C/C-SiC composites. In this work, C/C-SiC composites modified by h-BN (C/C-BN-SiC) were prepared by low-temperature compression molding (LTCM), pyrolysis and liquid silicon infiltration (LSI). Microstructure, oxidation behavior and kinetic characteristics of the C/C-BN-SiC composites were investigated compared with the C/C-SiC composite. Because h-BN is non-wetted by liquid silicon, the h-BN flakes in the matrix can obstruct and prolong the flow path of silicon, and protect the carbon fibers from corrosion to a certain extent. The oxidation kinetics of composites occur in low and high temperature domains, with different oxidation-controlling mechanisms, and the addition of h-BN can hinder the inward diffusion and lead to the decline of carbon recession and apparent activation energy.     

Tribological performance of B4C modified C/C-SiC brake materials under dry air and wet conditions

In this work, boron carbide (B₄C) was selected as additive to improve the tribological performance of C/C-SiC brake materials. It contained four phases (C, B₄C, Si and SiC) in B₄C modified C/C-SiC (C/C-B₄C-SiC) brake materials. Its wear rates were much less than that of C/C-SiC, especially at high braking speeds. The introduction of B₄C particles could reduce the braking temperature. During the braking process, B₄C in the material can be oxidized to B₂O₃. The flow of B₂O₃ could cover the interface of carbon fiber and PyC to prevent them from oxidation and thereby reduce the oxidative wear of the brake materials. Under wet conditions, the braking property of C/C-B₄C-SiC brake materials did not degrade, whereas the braking process was found to be stable.     

The effects of high-temperature annealing on microstructure and performance of Cf/C-SiC composites modified by FeSi2

FeSi₂ modified C/C-SiC composites (C/C-SiC-FeSi₂) are fabricated by chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI) with FeSi75 alloy. The effects of high-temperature annealing (1600?°C, 1650?°C, 1700?°C) on the microstructure and performance of C/C-SiC-FeSi₂ are investigated. With the elevation of annealing temperature, the porosity of the composites and the content of SiC increase due to the evaporation of liquid Si and the further reaction of Si and C. The mechanical performance gradually decreases due to the catalytic graphitization of the carbon fiber, the high porosity and the thermal residual stress (TRS) caused by thermal mismatch of different phases. The coefficient of thermal expansion and thermal diffusivity slightly decrease with increasing annealing temperature for the increase of porosity. However, the friction performance of the heat treated materials at high braking speed are greatly improved attributing to the increase of SiC content and the capturing and storage function of pores on hard particles.     

A novel approach for preparing a SiC coating on a C/C-SiC composite by slurry painting and chemical vapor reaction

In order to improve the oxidation resistance of C/C-SiC composites, a SiC coating was prepared on a C/C-SiC composite by slurry painting combined with a chemical vapor reaction process. The oxidation resistance and microstructural evolution of the coated samples were investigated. The results show that the as-prepared SiC coating contained a large amount of residual silicon, and the presence of these Si promoted the formation of a complete SiO₂ glass layer in the initial stage of oxidation. However, the evaporation of the residual Si also accelerated the failure of the SiC coating, which caused the weight loss of the sample to be about 2.2% after oxidation in static air at 1500 °C for 300 h. Attributed to a large number of SiC ceramics in the C/C-SiC composite, the oxidation weight loss rate of the coating sample after coating failure was reduced.     

Strength evolution of cyclic loaded LSI-based C/C-SiC composites

An experimental investigation was performed to study the influence of fatigue damage introduced by different loading cycles on the residual tensile strength (RTS) of plain-weave reinforced C_f/C-SiC composites (2D C/C-SiC). The specimens were subjected to the fatigue stress of 57 MPa for the preselected numbers of cycles as follows: 10², 10⁴ and 10⁵, respectively, before the static tensile test. The microstructures and fractured surfaces after the tensile test were examined by optical and scanning electron microscopy, respectively. The results showed that the RTS of the specimens after the preselected fatigue cycles numbers of 10², 10⁴ and 10⁵ increase to 89.8, 94.1 and 82.4 MPa, respectively, which are somewhat higher compared to the virgin samples (79.7 MPa). Additionally, we found that the linear part of the tensile stress-strain curve is independent on the fatigue cycles. Finally, the increased fatigue damage in C/C-SiC composites could determine a reduction of elastic modulus in all cases of fatigue tests.     

二维C/C复合材料层叠板制备工艺及其性能的研究

研究通过浸渍—炭化法制备二维C／C复合材料层叠板的工艺参数，分析了不同基体前驱体和增密次数对材料的密度、厚度和收缩率、体积电阻率和层间剪切强度的影响，并用扫描电子显微镜进行断口分析。结果表明：选用残炭率较高的基体前驱体和适当的增密次数是制备低成本二维C／C复合材料层叠板的关键；相同纤维体积的层叠板基体炭含量越高，电阻率越小，导电性能越好；单位体积含有炭纤维越多，纤维受损几率就越大，产生结构缺陷几率越高，导致电阻率增加，导电性能下降；本实验中二维C／C复合材料层叠板制备工艺简单可行，层叠板的密度达到1．40g／cm^3以上，剪切强度为1．5MPa，断口呈脆性断裂特征。