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%.     

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.     

Thermal fatigue behavior of C/C composites modified by SiC-MoSi2-CrSi2 coating

Carbon/carbon (C/C) composites were modified by SiC-MoSi₂-CrSi₂ multiphase coating by pack cementation, and their thermal fatigue behavior under thermal cycling in Ar and air environments was investigated. The modified C/C composites were characterized by scanning electron microscopy and X-ray diffraction. Results of tests show that, after 20-time thermal cycles between 1773 K and room temperature in Ar environment, the flexural strength of modified C/C samples decreased lightly and the percentage of remaining strength was 94.92%. While, after thermal cycling between 1773 K and room temperature in air for 20 times, the weight loss of modified C/C samples was 5.1%, and the flexural strength of the modified C/C samples reduced obviously and the percentage of remaining strength was only 75.22%. The fracture mode of modified C/C samples changed from a brittle behavior to a pseudo-plastic one as the service environment transformed from Ar to air. The decrease of the flexural strength during thermal cycle in air was primarily attributed to the partial oxidation of modified C/C samples.     

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 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.     

SiC nanowire-toughened MoSi2-SiC coating to protect carbon/carbon composites against oxidation

To protect carbon/carbon (C/C) composites against oxidation, a SiC nanowire-toughened MoSi₂-SiC coating was prepared on them using a two-step technique of chemical vapor deposition and pack cementation. SiC nanowires obtained by chemical vapor deposition were distributed random-orientedly on C/C substrates and MoSi₂-SiC was filled in the holes of SiC nanowire layer to form a dense coating. After introduction of SiC nanowires, the size of the cracks in MoSi₂-SiC coating decreased from 18 ± 2.3 to 6 ± 1.7 μm, and the weight loss of the coated C/C samples decreased from 4.53% to 1.78% after oxidation in air at 1500 °C for 110 h.     

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.     

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.     

Si-Mo-SiO2 oxidation protective coatings prepared by slurry painting for C/C-SiC composites

Three types of Si-Mo-SiO₂ coatings: two single-layered ones by different slurry paintings and a final sintering, and three-layered one by triple paintings followed by sintering each time, have been fabricated on the surface of C/C-SiC composites. The coatings were composed of SiC, MoSi₂, Si and SiO₂. The two single coatings had a microstructure with many pinholes and deep microcracks and had no obvious protection for C/C-SiC composites in air in the range of 1273-1673 K. While the triple Si-Mo-SiO₂ coating had a microstructure with much less defects and could provide more than 100 h protection at 1473-1673 K in air and kept intact in the course of 50 cycles of thermal shock test between 1673 K and 373 K. The excellent anti-oxidation ability and thermal shock resistance of the triple Si-Mo-SiO₂ coating can be attributed to its relatively integral microstructure and the self-sealing of microcracks 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。     

Microstructure and oxidation of multi-layer MoSi2-CrSi2-Si coatings for SiC coated carbon/carbon composites

Multi-layer MoSi₂-CrSi₂-Si anti-oxidation coatings with different compositional ratios were prepared on the surface of SiC coated carbon/carbon (C/C) composites by a two-step pack cementation method. The microstructure and anti-oxidation performance of the coating were studied. The results show that the multi-layered coatings could protect the C/C composites from oxidation in air at 1773 K for 1000 h or 1873 K for 750 h, respectively. The anti-oxidation performance of the multi-layer MoSi₂-CrSi₂-Si coating is mainly attributed to their dense and microcrack-free structure, appropriate thermal expansion coefficient and the well dispersed MoSi₂ and CrSi₂ in the coating.     

Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.     

A modified dual-layer SiC oxidation protective coating for carbon/carbon composites prepared by one-step pack cementation

To improve the oxidation resistance of SiC coating produced by pack cementation for carbon/carbon composites, a modified SiC coating has been produced by one-step pack cementation by adding ferrocene in pack compositions. The as-received coating exhibited a dual-layer dense structure, and oxidation protective ability of SiC coating could be improved by introducing ferrocene. The modified coating could protect C/C composites from oxidation for more than 100 h at 1673 K in air. The weight loss of the coated C/C composites was considered to arise from deflection of penetrating cracks formed in outer layer from inner layer to C/C matrix.     

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。     

B2O3 modified SiC–MoSi2 oxidation resistant coating for carbon/carbon composites by a two-step pack cementation

To protect carbon/carbon (C/C) composites against oxidation, a B₂O₃ modified SiC–MoSi₂ coating was prepared by a two-step pack cementation. The microstructure and the oxidation resistant property of the coating were studied. The results show that, the as-received coating is a dense structure, and is composed of α-SiC, β-SiC and MoSi₂. The B₂O₃ modified SiC–MoSi₂ coating has excellent oxidation resistant property, and can protect C/C composites from oxidation at 1773 K in air for more than 242 h. The failure of the coating was considered to arise from the existence of the penetration cracks in the coating during the slow cooling from 1873 to 673 K.     

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.     

SiC/ZrB2-SiC-B4C涂层的抗氧化和耐烧蚀性能研究

碳/碳化硅复合材料(C/SiC)在使用时经常受到高温氧化和烧蚀作用。本文采用化学气相沉积(CVD)和浆料刷涂-烧结法制备了双层SiC/ZrB2-SiC-B4C涂层,对比研究了无涂层,单层SiC涂层和双层SiC/ZrB2-SiC-B4C涂层C/SiC复合材料在1500℃下的氧化和在4.2 MW/m2热流密度下的烧蚀性能。结果表明,制备态ZrB2-SiC-B4C涂层致密、完整,表面平均粗糙度约为1 μm,孔隙率约为4.2 %。在1500℃氧化30 h后,SiC/ZrB2-SiC-B4C涂层C/SiC复合材料的质量损失率约为10%,涂层表面氧化膜致密,无明显裂纹。高温烧蚀20 s后,SiC/ZrB2-SiC-B4C涂层的线烧蚀率和质量烧蚀率分别为1.0±0.3 μm/s和1.1±0.2 mg/s,与单层SiC涂层相比分别降低了75.0 %和50.0 %,SiC/ZrB2-SiC-B4C涂层烧蚀后形成的ZrO2-SiO2氧化膜可以减缓火焰对复合材料的机械剥蚀作用。     

Bamboo-shaped SiC nanowire-toughened SiC coating for oxidation protection of C/C composites

An oxidation protective bamboo-shaped SiC nanowire-toughened SiC coating was prepared on the carbon/carbon composites by chemical vapor deposition and pack cementation. It is found that incorporating bamboo-shaped SiC nanowires makes the coating hardness and elastic modulus increase by 20.07% and 40.42% and microcrack density decrease by 84.04% due to their unusual toughening mechanism resulting from the nanoscale mechanical interlocking between the nodes and the surrounding matrix, resulting in a good oxidation inhibition for the coated samples. The result showed that the weight loss of the coated samples was only 0.5% after isothermal oxidation at 1500 °C for 72 h.