共查询到18条相似文献,搜索用时 216 毫秒
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采用水热电泳沉积法在SiC–C/C复合材料表面制备了纳米碳化硅和二硅化钼的复相(SiCn–MoSi2)抗氧化涂层。采用X射线衍射和扫描电子显微镜等对制备涂层的晶相组成、表面及断面微观结构进行了表征。研究了水热温度对制备涂层的结构及高温抗氧化性能的影响,分析了涂层在1 600℃静态氧化行为及失效机理。结果表明:外涂层主要由MoSi2和β-SiC晶相组成。复相外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高。SiCn–MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1 600℃氧化80 h后氧化质量损失为3.6×10–3 g/cm2。复合涂层在1 600℃的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层中出现贯穿性的裂纹和孔洞导致的。 相似文献
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采用水热电泳沉积法在SiC–C/C复合材料表面制备了纳米碳化硅和二硅化钼的复相(SiCn–MoSi2)抗氧化涂层。采用X射线衍射和扫描电子显微镜等对制备涂层的晶相组成、表面及断面微观结构进行了表征。研究了水热温度对制备涂层的结构及高温抗氧化性能的影响,分析了涂层在1 600℃静态氧化行为及失效机理。结果表明:外涂层主要由MoSi2和β-SiC晶相组成。复相外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高。SiCn–MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1 600℃氧化80 h后氧化质量损失为3.6×10–3 g/cm2。复合涂层在1 600℃的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层中出现贯穿性的裂纹和孔洞导致的。 相似文献
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原位合成TiB2-SiC基复相陶瓷及其高温摩擦学性能的研究 总被引:4,自引:0,他引:4
本研究以SiC为基体,用TiC和B4C为原料,采用新的反应原理生成TiB2,原位合成了TiB2-SiC基复相陶瓷,提高了SiC陶瓷的物理性能和高温摩擦学性能:随着材料中TiB2物相重量百分比的增加,材料的高温摩擦学性能提高。在以下摩擦环境参数下TiB2(wt25%)SiC基复相陶瓷自对偶在空气中高温摩擦磨损性能较好,呈现良好的高温自润滑性能:在升温状态下、空气中、环境温度为200℃-1000℃、外加载荷为0.2MPa、摩擦速度为0.3m/s,温度和外加载荷对TiB2-SiC基复相陶瓷自对偶比磨损率的影响具有依存性。高温摩擦氧化是TiB2-SiC基复相陶瓷自对偶高温磨损主要机理,磨损试样磨损断面包含摩擦氧化层、过渡层和基体亚表面三层。氧化层和过渡层接触紧密;磨屑具有典型包裹结构。 相似文献
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采用X射线衍射、扫描电镜和能谱分析技术研究了国外某MoSi2发热元件的组成和结构.结果表明:该MoSi2发热元件的主要组成为MoSi2、Mo5Si3以及以Al2O3和SiO2为主的玻璃相;黑色相和亮色相均匀分布在灰色基体中,亮色相主要伴随黑色相形成;断口以解理穿晶特征为主.MoSi2发热元件表面有一层20μm厚的以SiO2和Al2O3为主的玻璃保护膜,在保护膜表面有大量针状凸起生成.保护膜外表面形貌以及发热元件中黑色相和保护膜表面针状凸起中Al含量的增加是该MoSi2发热元件区别国内外其它MoSi2发热元件的主要特征. 相似文献
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在SiC粉中添加MoSi2粉,采用模压成型、无压烧成方法制备MoSi2–再结晶SiC(RSiC)复合材料。利用扫描电子显微镜、X射线衍射和等温氧化法研究复合材料的高温抗氧化性能及氧化机理。结果表明,所得复合材料中SiC为6H型,部分MoSi2转变为六方结构Mo4.8Si3C0.6,添加MoSi2前后样品的氧化产物均为方石英,样品表面生成的氧化膜形貌相似。氧化过程中样品质量变化与时间关系遵循抛物线规律,随MoSi2添加量增加,复合材料的抗氧化性能显著提高,其中,添加20%(质量分数)MoSi2所得复合材料在1500℃循环氧化100h后质量增加量仅为未添加MoSi2样品的37%。当MoSi2添加量为10%时,复合材料的抗氧化性能随样品烧成温度的升高先提高后降低,2 300℃烧成所得材料有较好的高温抗氧化性能,其氧化速率常数为0.99mg2/(cm4.h)。在氧化初始阶段,Mo4.8Si3C0.6和MoSi2首先发生氧化反应,随氧化时间增加,Mo4.8Si3C0.6和MoSi2消耗殆尽,此后的氧化则主要为Mo5Si3和SiC的氧化。SiO2膜的致密性和膜厚度与膜中Mo5Si3的含量有关。 相似文献
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Zujie Zheng Hongsheng Zhao Ziqiang Li Xiaoxue Liu Bin Wu Bing Liu 《Ceramics International》2018,44(5):4795-4800
ZrSi2-SiC/SiC coating was prepared on the surface of high temperature gas-cooled reactor (HTR) matrix graphite spheres by two-step pack cementation and sintering process. The microstructure, oxidation resistance and thermal shock resistance properties of the as-prepared coatings with different original powder mixtures were investigated. Results show that dense microstructure of the ZrSi2-SiC/SiC coating and continuous ZrSiO4-SiO2-ZrO2 glass phase generated during the oxidation process were the key factors for the outstanding thermal properties. When the mole ratio of Zr:Si:C reaches 1:7:3 in the second pack cementation powders, the coated graphite spheres have optimum oxidation resistant ability. The weight gain is only 0.6 wt% after 15 times thermal shock tests and 0.12 wt% after isothermal oxidation test at 1500 °C for 20 h in air. The oxidation resistant mechanism of the coating was also discussed. The dense inner SiC layer and the outer glass layer generated during the oxidation process could protect the ZrSi2-SiC/SiC coating from further oxidation. 相似文献
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《Diamond and Related Materials》2000,9(3-6):439-445
The growth of β-SiC films via chemical vapor deposition (CVD) has been under intensive investigation because this is viewed to be an enabling material for a variety of new semiconductor devices in areas where silicon cannot effectively compete. However, the difficulty in achieving single-crystal or highly textured surface morphology in films with low bulk defect density has limited the use of β-SiC films in electronic devices. Although several researchers have reported results relating the morphology of β-SiC films to deposition parameters, including substrate temperature and gas composition, detailed knowledge of the effects of deposition parameters on film morphology and crystallographic texture is still lacking. If these relationships between deposition parameters and film morphology can be quantified, then it may be possible to obtain optimal β-SiC film morphologies via CVD for specific applications such as high-power electronic devices.The purpose of this study is to predict the dependence of the surface morphology of β-SiC films grown by CVD on substrate temperature and inlet atom ratio of Si:C, and to model the morphological evolution of the growing polycrystalline film. The Si:C ratio is determined by the composition of the reactant gases, propane (C3H8) and silane (SiH4). A two-dimensional numerical model based on growth rate parameters has been developed to predict the evolution of the surface morphology. The model calculates the texture, surface roughness, and grain size of continuous polycrystalline β-SiC films resulting from growth competition between nucleated seed crystals of known orientation. Crystals with the fastest growth direction perpendicular to the substrate surface are allowed to overgrow all other crystal orientations. When a continuous polycrystalline film is formed, the facet orientations of crystals are represented on the surface. In the model, the growth parameter α2D, the ratio of the growth rates of the {10} and {11} faces, determines the crystal shapes and, thus, the facet orientations of crystals. The growth rate parameter α2D used in the model has been derived empirically from the textures of continuous β-SiC films reported in the literature. 相似文献
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Surfaces featuring gradients of chemical composition and/or morphology allow high-throughput investigations and systematic studies in disciplines such as physics, chemistry, materials science, and biology. In this work, novel diamond/β-SiC composite films exhibiting a gradient composition were synthesized by a hot filament chemical vapor deposition (HFCVD) technique utilizing H2, CH4, and tetramethylsilane (TMS) as reaction gases. A specific filament-sample arrangement in the HFCVD chamber induced a gradation in chemical composition of the gas phase above the substrate surface, which, in turn, leads to a gradual change in the composition of the deposited films potentially ranging from pure diamond to pure β-SiC. It was possible to control the actual details of the diamond/β-SiC ratio in the gradient films by adjusting deposition pressure and TMS concentration. Aside from film characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to determine the presence and quality of both diamond and β-SiC phases, respectively. The wealth of information provided by such diamond/β-SiC composite films allowed for a systematic investigation of the mechanism governing their growth. It turned out, that the growth process features nonequilibrium characteristics. It is dominated by a competition between a kinetic product (diamond) and kind of a thermodynamic product (β-SiC) to occupy any available positions on the substrate and the growing surface, respectively. With higher hydrogen radical concentration [H] and substrate temperature, the deposition is kinetically controlled, leading to diamond dominated films. On the other hand, a lower [H] and substrate temperature, consequently resulted in a predominantly thermodynamically controlled deposition, featuring a higher β-SiC content in the film. 相似文献
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采用包渗法在Mo及Mo?W基体上分别制备MoSi2及(Mo,W)Si2涂层,研究了W掺杂对MoSi2涂层抗氧化性能的影响规律和作用机理。结果表明,W元素固溶到MoSi2涂层中,形成(Mo,W)Si2固溶体,涂层微观结构更加致密化。在1600℃高温下静态氧化,(Mo,W)Si2涂层抗氧化失效时间长达70 h,1200℃下氧化1000 h仍具有良好的防护性能,抗氧化性能大幅提升。加入W元素阻碍了Si元素与基体间的扩散反应,降低了涂层中Si元素的消耗速率,显著增强了(Mo,W)Si2涂层抗高温氧化性能。在500℃低温下静态氧化50 h,与MoSi2涂层相比,(Mo,W)Si2涂层氧化产生明显的“Pest”现象,涂层严重粉化失效。加入W元素降低了涂层中Si元素的扩散速率,导致低温下涂层表面无法形成致密氧化层,加剧涂层的快速氧化。 相似文献
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《Ceramics International》2022,48(3):3206-3215
B4C modified HfB2-SiC coating for C/C substrate was designed to expand the application of HfB2-SiC based coating in low-medium temperature environment. The oxidation protection behavior of HfB2-SiC based ceramic coatings with and without B4C at 1073, 1273 and 1473 K was tested and analyzed. The experimental results reveal that the oxidative damage of HfB2-SiC coated C/C reduces by over 20% after introducing B4C, which may be due to the protection of borosilicate glass with more suitable viscosity during oxidation. Meanwhile, B4C can improve the oxidation protection ability of HfB2-SiC coating best at 1473 K. And the introduction of B4C can reduce the mass loss of HfB2-SiC coated C/C sample by 77.6% after oxidation for 58 h at 1473 K. The fluidity of glass film becoming better with temperature-rising, and the fluid borosilicate glass layer makes the coated samples have the best anti-oxidation properties at 1473 K among these three temperatures. 相似文献
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Xuanru Ren Lifeng Wang Peizhong Feng Ping Zhang Litong Guo Xiaojun Sun Hongsheng Mo Ziyu Li 《Ceramics International》2018,44(13):15517-15525
To reveal the generation mechanisms of the Ta-Si-O glass ceramics layer in dynamic oxidation environments, a 40?wt% TaB2-SiC coating was prepared by liquid phase sintering method. To obtain pure phase TaB2 powders at lower temperature (1500?°C), excessive B2O3 powders were added in raw materials to eliminate the TaC byproduct phase. The hexagonal pure phase TaB2 powders own average particle size of about 386?nm. During the TGA dynamic oxidation tests, after the modification of 40?wt% TaB2, the initial weight loss temperature of the sample delayed by about 48%, while the weight loss percentage and rate in fastest weight loss zone decreased by about 61% and 53%, respectively. During oxidation, the generated Ta-oxides were peeled and carried away by the formed fluid SiO2 glass layer to form “Ta-oxides halation” at first, which results the dissolution of Ta-oxides in the SiO2 glass, thus forming the Ta-Si-O glass ceramics with dendritic structure. With the spread of the SiO2 glass layer and growth of the Ta-Si-O dendrite, the Ta-Si-O glass ceramics gradually cover on the surface of the SiO2 glass layer, forming the structure of Ta-Si-O/SiO2 double glass layer that is capable of sealing and arresting of microcracks. 相似文献
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