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.     

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.     

Microstructure and anti-oxidation property of Si-W-Cr coating for SiC coated carbon-carbon composites

To protect carbon/carbon (C/C) composites from oxidation at high temperature, a Si-W-Cr coating was prepared on the surface of SiC coated C/C composites by a simple pack cementation technique. The microstructure and phase composition of the as-received multi-coating were examined by SEM, XRD and EDS. The coating obtained by first step pack cementation was porous α-SiC structure. New phases of WSi₂ and CrSi₂ together with α-SiC deposited on the porous SiC inner layer. Oxidation test shows that the weight loss of single SiC coated C/C is up to 8.21% after 9 h in air at 1773 K, while the weight loss of Si-W-Cr/SiC coated C/C composites is only 2.26% after 51 h. After thermal cycling between 1773 K and room temperature for 40 times, the weight loss is only 3.36%. The weight loss of coated C/C composites was primarily due to the reaction of C/C matrix and oxygen diffusing through the penetrable cracks in the coating.     

Effect of Thermal Shock and Oxidation on Mechanical Property of Carbon/Carbon Composites with a Silicide Coating

A SiC whisker-toughened MoSi2-SiC-Si coating was prepared on carbon/carbon (C/C) composites surface by a two-step technique of slurry and pack cementation, and the effects of thermal shock and oxidation on the mechanical property of the coated C/C were studied. The flexural strength of C/C composites was improved by 6.8% after coated by SiC whisker-toughened MoSi2-SiC-Si. After thermal cycle between 1773 K and room temperature in air for 10 times, the mass loss of the coated sample was 5.08% and the percent...     

磁控溅射法制备碳/碳复合材料 SiC/MoSi2-ZrB2 涂层的结构及抗氧化性能研究

通过磁控溅射法在碳/碳复合材料表面成功制得了SiC/MoSi2-ZrB2陶瓷涂层并对结构及其在高温有氧环境中的抗氧化性能进行了研究。结果表明制备的SiC/MoSi2-ZrB2陶瓷涂层呈柱状晶结构且均匀性良好,其在1273K和1773K的有氧环境中氧化60min失重率分别是5.6×10-2 g/cm2 和 6.3×10-2 g/cm2。     

C/SiC/MoSi2–Si multilayer coatings for carbon/carbon composites for protection against oxidation

To improve the oxidation resistance of carbon/carbon (C/C) composites, a C/SiC/MoSi₂–Si multilayer oxidation protective coating was prepared by slurry and pack cementation. The microstructure of the as-prepared coating was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The isothermal oxidation and erosion resistance of the coating was investigated in electrical furnace and high temperature wind tunnel. The results showed that the multilayer coating could effectively protect C/C composites from oxidation in air for 300 h at 1773 K and 103 h at 1873 K, and the coated samples was fractured after erosion for 27 h at 1873 K h in wind tunnel. The weight loss of the coated specimens was considered to be caused by the formation of penetration cracks in the coating. The fracture of the coated C/C composites might result from the excessive local stress in the coating.     

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.     

SiC–MoSi2/ZrO2–MoSi2 coating to protect C/C composites against oxidation

To improve the oxidation resistance of carbon/carbon (C/C) composites in air at high temperatures, a SiC–MoSi₂/ZrO₂–MoSi₂ coating was prepared on the surface of C/C composites by pack cementation and slurry method. The microstructures and phase compositions of the coated C/C composites were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The result shows that the SiC–MoSi₂/ZrO₂–MoSi₂ coating is dense and crack-free with a thickness of 250–300 μm. The preparation and the high temperature oxidation property of the coated composites were investigated. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 260 h at 1773 K in air. The excellent anti-oxidation performance of the coating is considered to come from the formation of ZrSiO₄, which improves the stability of the coating at high temperatures.     

Cr含量对炭/炭复合材料SiC/Al-Si抗氧化涂层的影响(英文)

采用料浆法在已制得SiC内涂层炭/炭(C/C)复合材料(SiC-C/C)表面,制备了不同Cr含量(质量分数分别为0%,31.85%,44.95%及55.57%)的Al-Si合金涂层。分别采用X射线衍射法(XRD)、扫描电子显微镜(SEM)及1773K静态空气气氛中的恒温氧化试验,测试了所得涂层试样的微观结构及抗氧化性能。结果表明:Cr元素可以显著提高Al-Si合金涂层的抗氧化性能;Cr含量为44.95%的Al-Si合金涂层SiC-C/C复合材料试样在1773K空气气氛中氧化197h后的氧化增重为0.079%(质量分数)。     

ZrSiO4 Oxidation Protective Coating for SiC-Coated Carbon/Carbon Composites Prepared by Supersonic Plasma Spraying

To protect carbon/carbon (C/C) composites against oxidation, ZrSiO₄ oxidation protective coating was prepared on SiC-coated C/C composites by supersonic plasma spraying. X-ray diffraction and scanning electron microscopy were used to analyze the phase and microstructure of the coating. The results show that the as-prepared ZrSiO₄ coating is continuous and well bonded with the SiC inner layer without penetrating crack, which exhibits good oxidation-resistant properties. After oxidation at 1773 K in air for 97 h and nine thermal shock cycles between 1773 K and room temperature, the weight loss of the coated C/C composites was only 0.08%. The excellent oxidation-resistant properties of the coating were attributed to its dense structure and the formation of the stable ZrO₂-SiO₂ glassy mixture on the surface of ZrSiO₄ coating.     

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.     

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.     

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%.     

硅钽含量对C/C复合材料SiC/TaSi_2复合涂层结构和抗氧化性能的影响

采用包埋技术在C/C复合材料表面制备SiC/TaSi2抗氧化复合涂层,通过恒温氧化实验以及X射线衍射分析、扫描电镜观察,研究了包埋粉料中硅钽含量对复合涂层微观结构和高温抗氧化性能的影响.结果表明,随着硅钽比的减小,复合涂层的厚度先增大后减小;硅钽比为5:1所制备的复合涂层具有相对较大的厚度和较为致密的结构,且TaSi2含量相对较高,体现出优良的抗氧化和抗热震性能,在1500℃氧化241.8 h和经过18次1500℃←室温急冷急热后,带有该涂层的C/C试样失重仅为1.04%.穿透性裂纹的形成是长时间氧化后涂层失效的主要原因.     

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

To protect carbon/carbon (C/C) composites against oxidation, a MoSi₂ outer coating was prepared on pack-cementation SiC coated C/C composites by a hydrothermal electrophoretic deposition. The phase composition, microstructure and oxidation resistance of the prepared MoSi₂/SiC coatings were investigated. Results show that hydrothermal electrophoretic deposition is an effective route to achieve crack-free MoSi₂ outer coatings. The MoSi₂/SiC coating can protect C/C composites from oxidation at 1773 K for 346 h with a weight loss of 2.49 mg cm⁻² and at 1903 K for 88 h with a weight loss of 5.68 mg cm⁻².     

C/SiC/MoSi2–SiC–Si multilayer coating for oxidation protection of carbon/carbon composites

C/SiC/MoSi₂–SiC–Si oxidation protective multilayer coating for carbon/carbon (C/C) composites was prepared by pack cementation and slurry method. The microstructure, element distribution and phase composition of the as-received coating were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the multilayer coating was composed of MoSi₂, SiC and Si. It could effectively protect C/C composites against oxidation for 200 h with the mass loss of 3.25% at 1873 K in static air. The mass loss of the coated C/C composites results from the volatilization of SiO₂ and the formation of cracks and bubble holes in the coating.     

SiC-Glass涂层碳/碳复合材料的中低温氧化行为及机制研究

为揭示具有良好高温(1300～1600 ℃)抗氧化性能的SiC-Glass涂层在中低温(500～1200 ℃)条件下的氧化防护性能,对SiC-Glass涂层碳/碳(C/C)复合材料的中低温氧化行为和机制进行了系统研究.结果表明,SiC-Glass涂层C/C复合材料的中低温氧化失重服从直线规律,但氧化机制存在温度依赖性,可分为2个区段:(1) 低温区(500～800 ℃),氧化失重速率与温度服从Arrhenius关系,氧化主要受控于氧在涂层缺陷内的扩散速率;(2) 在中温区(800～1200 ℃),氧化失重速率与温度不服从Arrhenius关系,氧化过程受氧在涂层缺陷中的扩散、SiC内涂层材料的氧化、Glass外涂层的部分熔融愈合等多种因素联合控制.对比分析表明,SiC-Glass涂层的中低温抗氧化性能不及其高温抗氧化性能优异.中低温下,涂层缺陷愈合不充分是导致这一现象的主要原因.     

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.     

Anti-oxidation properties of ZrB2 modified silicon-based multilayer coating for carbon/carbon composites at high temperatures

To improve the anti-oxidation ability of silicon-based coating for carbon/carbon (C/C) composites at high temperatures, a ZrB₂ modified silicon-based multilayer oxidation protective coating was prepared by pack cementation. The phase composition, microstructure and oxidation resistance at 1773, 1873 and 1953 K in air were investigated. The prepared coating exhibits dense structure and good oxidation protective ability. Due to the formation of stable ZrSiO₄–SiO₂ compound, the coating can effectively protect C/C composites from oxidation at 1773 K for more than 550 h. The anti-oxidation performance decreases with the increase of oxidation temperature. The mass loss of coated sample is 2.44% after oxidation at 1953 K for 50 h, which is attributed to the decomposition of ZrSiO₄ and the volatilization of SiO₂ protection layer.     

Double-layer oxidation protective SiC/Cr-Al-Si coating for carbon-carbon composites

Double-layer oxidation resistant SiC/Cr-Al-Si coating for carbon-carbon composites was prepared by a two-step method of pack cementation and slurry. The phase composition, micro-structure and oxidation resistance of mono-layer SiC coating and double-layer SiC/Cr-Al-Si coating were studied by XRD, SEM, and isothermal oxidation test at 1773 K in air, respectively. Mono-layer SiC coating consists of SiC and Si, which can protect carbon-carbon composites for several hours depending on its thin thickness and porous structure. After adding outer Cr-Al-Si alloy coating, the as-prepared double-layer SiC/Cr-Al-Si coating with a dense surface and about 150 μm thickness showed improved oxidation resistance, which can protect carbon-carbon composites for 197 h with only 0.079 wt.% mass gain. The failure of the double-layer SiC/Cr-Al-Si coating is thought to occur due to the excessive depletion of the outer Cr-Al-Si alloy coating and the appearance of defects in the SiO₂ glass layer.