Double SiC coating on carbon/carbon composites against oxidation by a two-step method

To improve the oxidation resistance of C/C composites, a double SiC protective coating was prepared by a two-step technique. Firstly, the inner SiC layer was prepared by a pack cementation technique, and then an outer uniform and compact SiC coating was obtained by low pressure chemical vapor deposition. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD analyses. Oxidation behaviour of the SiC coated C/C composites was also investigated. It was found that the double SiC coating could protect C/C composites against oxidation at 1773 K in air for 178 h with a mass loss of 1.25%. The coated samples also underwent thermal shocks between 1773 K and room temperature 16 times. The mass loss of the coated C/C composites was only 2.74%. Double SiC layer structures were uniform and dense, and can suppress the generation of thermal stresses, facilitating an excellent anti-oxidation coating.     

ZrB2-MoSi2/SiC涂层C/C复合材料的制备及氧化性能（英文）

为了提高C/C复合材料的抗氧化性,在C/C复合材料基体上制备了ZrB2-MoSi2/SiC涂层。采用包埋法制备SiC中间层,采用喷涂法制备ZrB2-MoSi2外涂层。用XRD和SEM分别分析、测试所制备涂层的物相组成和显微结构,研究涂层复合材料的高温抗氧化性能。结果表明:C/C复合材料的外涂层由ZrB2、MoSi2和SiC三相组成;在1273K和1773K下分别氧化30h和10h后ZrB2-MoSi2/SiC涂层试样的质量损失分别为5.3%和3.0%,涂层表面长有纳米SiC晶须。C/C复合材料ZrB2-MoSi2/SiC涂层具有自愈合特性和良好的高温抗氧化性能。     

原位生长碳纳米管对化学气相沉积SiC涂层的影响

以碳/碳复合材料为基体,MTS为先驱体原料,采用化学气相沉积法在复合材料表面制备CNT-SiC/SiC复合涂层;研究原位生长的碳纳米管(CNTs)对SiC沉积速度和微观形貌的影响。结果表明:CNTs加快SiC的沉积,涂层的平均质量增加速率提高5%,提高沉积的均匀性,且晶粒更细小;经1 100℃恒温氧化10 h后,单一SiC涂层、CNT-SiC/SiC涂层的质量损失率分别为41.11%和34.32%;经(1 100℃,3 min)(室温,3 min)热循环15次后,单一SiC涂层和CNT-SiC/SiC涂层的质量损失率分别为33.17%和30.25%,部分区域涂层脱落及涂层表面形成的气孔是涂层试样质量损失的主要原因。     

碳/碳复合材料SiC/W-Al-Si涂层微观结构及抗氧化性能

分别采用包埋法、料浆法在碳/碳（C/C）复合材料表面制备了碳化硅（SiC）内涂层、W-Al-Si合金外涂层,借助XRD和SEM分析了所得涂层的物相组成和微观结构,并测试了带有单一SiC涂层、SiC/W-Al-Si双涂层碳/碳复合材料试样在1500℃静态空气中的抗氧化性能。结果表明：富Si的SiC内涂层结构疏松,仅能为碳/碳基体提供数小时的防氧化保护;W-Al-Si合金外涂层主要由WSi2和W（Si,Al）2两相组成;SiC/W-Al-Si双涂层厚度约为100μm,其抗氧化性能明显优于单一SiC涂层,氧化19 h后涂层试样的质量损失未超过5%;有望进一步通过优化W-Al-Si外涂层料浆比例,避免因为与SiC内涂层热膨胀不匹配而产生透性裂纹,从而发挥出超过19 h后SiC/W-Al-Si双涂层的氧化防护潜力。     

炭/炭复合材料表面SiC/ZrSiO4-SiO2复合涂层的抗氧化性能与红外发射特性研究

为提高炭/炭(C/C)复合材料的高温抗氧化性能并降低其红外发射率,采用包埋–刷涂法在其表面制备了SiC/ZrSiO_4-SiO_2复合涂层。借助XRD、SEM等表征分析了涂层的成分与微观结构,并研究了SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料在1500℃动态空气条件下的抗氧化性能,以及在90和500℃下的红外发射率。结果表明:由疏松结构SiC内涂层和镶嵌结构ZrSiO_4-SiO_2外涂层组成的SiC/ZrSiO_4-SiO_2复合涂层具有优异的抗氧化性能,在1500℃流动空气(0.6 L/min)等温氧化条件下氧化50 h后试样的氧化失重率仅为0.03%。在C/C复合材料表面制备SiC/ZrSiO_4-SiO_2复合涂层后其红外发射率明显降低,并随温度升高而越低。复合涂层包覆试样在90℃时3~5μm和8~14μm波段的平均红外发射率分别为0.55和0.66;在500℃时3~5μm和8~14μm波段的平均红外发射率分别为0.48和0.62。SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料可作为优良的低红外发射率高温热结构材料应用于航空航天领域。     

A ZrSiO4/SiC oxidation protective coating for carbon/carbon composites

In order to improve the oxidation resistance of carbon/carbon (C/C) composites, a ZrSiO₄ coating on SiC pre-coated C/C composites was prepared by a hydrothermal electrophoretic deposition process. Phase compositions and microstructures of the as-prepared ZrSiO₄/SiC coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The anti-oxidation property and failure mechanism of the multi-layer coating were investigated. Results show that hydrothermal electrophoretic deposition is an effective route to prepare crack-free ZrSiO₄ outer coatings. The multi-layer coating obviously exhibits two-layer structure. The inner layer is composed of SiC phase and the outer layer is composed of ZrSiO₄ phase. The bonding strength between the outer layer coatings and C/C–SiC substrate are 30.38 MPa. The ZrSiO₄/SiC coating displays excellent oxidation resistance and can protect C/C composites from oxidation at 1773 K for 332 h with a mass loss rate of only 0.48 × 10^− 4 g/cm²·h. The mechanical properties of the specimens are 84.36 MPa before oxidation and 68.29 MPa after oxidation. The corresponding high temperature oxidation activation energy of the coated C/C composites at 1573–1773 K is calculated to be 119.8 kJ/mol. The oxidation process is predominantly controlled by the diffusion rate of oxygen through the ZrSiO₄/SiC multi-coating. The failure of the coating is due to the formation of penetrative holes between the SiC bonding layer and the C/C matrix at 1773 K.     

Anti-oxidation behavior of chemical vapor reaction SiC coatings on different carbon materials at high temperatures

To protect carbon materials from oxidation, SiC coatings were prepared on carbon/carbon(C/C) composites and graphite by chemical vapor reaction. SEM and XRD analyses show that the coatings obtained are composed of SiC grains and micro-crystals. The influence of different carbon substrates on oxidation behavior of coated samples was investigated, and then their oxidation mechanisms were studied. Oxidation test shows that the SiC coated graphite has a better oxidation resistance than SiC coated C/C composites at high temperatures (1 623 K and 1 823 K). In the oxidation process, the oxidation curves of SiC coated C/C composites are linear, while those of SiC coated graphite follow a quasi-parabolic manner. The oxidation mechanism of the former is controlled by chemical reaction while the latter is controlled by oxygen diffusion based on the experimental results. The variation of oxidation behavior and mechanism of SiC coatings on two kinds of carbon substrates are primarily contributed to their structure differences.     

SiC nanowire-toughened SiC-MoSi2-CrSi2 oxidation protective coating for carbon/carbon composites

To prevent carbon/carbon (C/C) composites from oxidation, a dense SiC nanowire-toughened SiC-MoSi₂-CrSi₂ multiphase coating was prepared by the two-step technique composed of chemical vapor deposition (CVD) and pack cementation. The coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SiC nanowires could decrease the dimension of cracks and improve the oxidation and thermal shock resistance of SiC-MoSi₂-CrSi₂ multiphase coating. Oxidation test shows that, after introducing SiC nanowires, the weight loss of the coated sample can be reduced from 1.06% to 0.64% after oxidation at 1773 K for 155 h and decreased from 6.92% to 3.42% after thermal cycling between 1773 K and room temperature for 30 times.     

HfB2/SiC as a protective coating for 2D Cf/SiC composites: Effect of high temperature oxidation on mechanical properties

In the field of thermal shielding for aerospace applications C_f/SiC composites are raising great interest, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular HfB₂, are among the best oxidation resistant materials known. A coating made of a HfB₂/SiC composite (20% weight SiC) was tested as an oxidation protection on a C_f/SiC composite. The composite was produced by Polymer Impregnation Pyrolysis (PIP), which is a simple and low cost method; the coating was applied by painting a slurry on the surface of the composite and by heat treating. The thermal behaviour was studied by thermo-gravimetric analysis, and mechanical tests were conducted before and after oxidation. The HfB₂/SiC composite seems to effectively protect the underlying C_f/SiC composite, with a mechanical strength reduction of only 20% after 30 min at 1600 °C, even if some weight loss due to partial carbon fibre damage is observed. A first analysis of thermal cycling in oxidizing environment suggested that the HfB₂/SiC coating reduces continual damage thanks to the sealing effect of the glassy surface layer.     

Fabrication of Y2Si2O7 coating and its oxidation protection for C/SiC composites

Yttrium silicate (Y₂Si₂O₇) coating was fabricated on C/SiC composites through dip-coating with silicone resin + Y₂O₃ powder slurry as raw materials. The synthesis, microstructure and oxidation resistance and the anti-oxidation mechanism of Y₂Si₂O₇ coating were in–estigated. Y₂Si₂O₇ can be synthesized by the pyrolysis of Y₂O₃ powder filled silicone resin at mass ratio of 54.2:45.8 and 800 °C in air and then heat treated at 1400 °C under Ar. The as-fabricated coating shows high density and fa–orable bonding to C/SiC composites. After oxidation in air at 1400, 1500 and 1600 °C for 30 min, the coating-containing composites possess 130%–140% of original flexural strength. The desirable thermal stability and the further densification of coating during oxidation are responsible for the excellent oxidation resistance. In addition, the formation of eutectic Y–Si–Al–O glassy phase between Y₂Si₂O₇ and Al₂O₃ sample bracket at 1500 °C is disco–ered.     

Si-W-Mo coating for SiC coated carbon/carbon composites against oxidation

In order to prevent carbon/carbon (C/C) composites from oxidation at 1773 K, a Si-W-Mo coating was prepared on the surface of SiC coated C/C composites by a simple pack cementation technique. The microstructures and phase composition of the as-received multi-coating were examined by SEM, XRD and EDS. It was seen that the compact multi-coating was composed of α-SiC, Si and (W_xMo_1 − x)Si_2. Oxidation behaviour of the SiC/Si-W-Mo coated C/C composites was also studied. After 315 h oxidation in air at 1773 K and thermal cycling between 1773 K and room temperature for 17times, no weight loss of the as-coated C/C composites was measured. The excellent anti-oxidation ability of the multi-coating is attributed to its dense structure and the formation of the stable glassy SiO₂ film on the coating surface during oxidation.     

SiC/MoSi2高温抗氧化涂层的制备及性能探究

采用磁控溅射法在C/C复合材料表面制备SiC/MoSi2抗氧化涂层,并利用SEM、XRD以及EDS等测试手段对涂层的组织结构、抗氧化性能以及抗氧化机制进行了研究。结果表明,所得涂层结构致密、厚度均匀可控,呈柱状晶。在1500℃静态氧化60min后,涂层试样表现出了较优异的抗氧化性能,氧化质量损失仅为3.2x10-2g/cm-2。导致C/C基体被氧化失重的主要原因是涂层中沿晶界产生的贯穿裂纹为氧气进入基体表面提供了通道。     

C/C复合材料航空刹车副表面防氧化涂料的研制

以磷酸,磷酸盐,ＳｉＣ,ＳｉＯ２,Ｂ４Ｃ和含硼化合物等为原料研制了以硅、硼化合物为主的多组分陶瓷混合物涂料。采用该涂料以刷涂的方式制备的Ｃ／Ｃ复合材料复合涂层具有显著的防氧化效果。研究表明,涂覆有涂层的Ｃ／Ｃ复合材料试样在９００℃氧化１０ｈ后,其氧化损失率为１０．３７％;试样在空气中９００℃,３ｍｉｎ＝室温,２ｍｉｎ急冷急热,如此在１０ｈ内循环１００次后,氧化损失率为８．４１％,涂层与基体结合牢固     

原位自生C/C复合材料SiC涂层的物相组成与形成机理

利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)等检测手段,观察并研究了原位自生C/C复合材料SiC涂层的物相组成和显微结构特点,并根据SiC固态相变规律和元素互扩散原理,探讨了低压Ar气氛反应烧结制备SiC涂层的形成机理。结果表明,低压保护气氛的引入显著提高了反应烧结过程中液态Si在C/C复合材料表面的润湿性,促进C、Si原子互扩散。在此条件下,多晶Si粉与石墨碳反应形成β-SiC稳定相,且该涂层内部衬度均匀,具有鳞片状和细针状纳米晶须结构,从而改善了C/C复合材料的生物相容性。     

A MoSi2-SiC-Si oxidation protective coating for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a dense coating has been produced by a two-step pack cementation technique. XRD and SEM analysis shows that the as-obtained coating was composed of MoSi₂, SiC and Si with a thickness of 80-100 μm. The MoSi₂-SiC-Si coating has excellent anti-oxidation property, which can protect C/C composites from oxidation at 1773 K in air for 200 h and the corresponding weight loss is only 1.04%. The weight loss of the coated C/C composites is primarily due to the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating.     

SiC/SiC–YAG–YSZ oxidation protective coatings for carbon/carbon composites

SiC/SiC–YAG–YSZ coatings were prepared by pack cementation, chemical vapor deposition and slurry painting on carbon/carbon (C/C) composites. The microstructures and oxidation behavior of coatings were investigated. The results show that the coatings displayed good oxidation and thermal shock resistance due to a dense glassy layer with silicates formed on the coating of SiC–YAG–YSZ. The weight gain rate of coated C/C composites was 1.77% after oxidation for 150 h at 1773 K. SiC in outer coating can promote the formation of oxygen diffusion barrier and lead to the optimum oxidation resistance for the coatings, compared with YSZ and YAG.     

ZrO2–SiO2 gradient multilayer oxidation protective coating for SiC coated carbon/carbon composites

In order to eliminate the mismatch of thermal expansion coefficient between the ZrO₂ outer layer and the internal bonding SiC layer, ZrO₂–SiO₂ composition-gradient transition layers were prepared by a sol–gel technique using tetraethoxysilane (TEOS) and zirconyl chloride as source materials. Energy dispersive spectroscopy (EDS) analysis displays that the gradient composition ZrO₂–SiO₂ outer coating could be obtained by immersing the SiC precoated carbon/carbon (C/C) composites into the gradient composition zirconia-silica sols (ZS sol) in turn. Oxidation test shows that, after 10 h oxidation in air at 1773 K, the weight loss of the gradient ZrO₂–SiO₂ coating coated SiC-C/C is only 1.97%.     

熔硅浸渗工艺快速制备C/SiC复合材料的非等温氧化行为

以针刺整体毡为预制体,采用化学气相沉积（CVD）增密制备C/C多孔体,用熔硅浸渗（MSI）工艺快速制备C/SiC复合材料,通过非等温热重分析研究材料低温下的氧化反应动力学和反应机理。结果表明：C/SiC材料的非等温氧化过程呈现自催化特征,氧化机理为随机成核,氧化动力学参数为l：g（A/min^-1）=8.752,Ea=169.167 kJ/mol。MSI工艺中,纤维因硅化损伤产生的活性碳原子易先发生氧化,使C/SiC材料起始氧化温度仅为524℃,比C/C材料约低100℃,且氧化产生大量的裂纹和界面,使材料在氧化初期即具有大的氧化反应速率,C/C材料则出现氧化反应速率滞后现象。     

Study of fluorhydroxyapatite coatings on carbon/carbon composites

Fluorhydroxyapatite coatings were prepared on the surface of carbon/carbon composites using the combined action of ultrasonic-electrodeposition and ion exchange. The morphology, structure and composition of the prepared coatings after ion exchange were investigated by scanning electron microscopy, X-ray energy spectrum analysis, infrared spectroscopy and X-ray diffraction. Results show that the crystallinity of the coating as well as the intensity of the diffraction peaks (112) and (300) of hydroxyapatite increased, whereas the intensity of the diffraction peaks of tricalcium phosphate decreased. The small lamellar crystals were converted into large ones. The fluorine content in the coating was 4.59%. The bonding strength between the coating and the carbon/carbon matrix increased slightly after immersion, reaching 4.12 MPa. The mechanism of the ion exchange during which hydroxyapatite turned into fluorhydroxyapatite is discussed.