碳/碳复合材料SiC-HfSi_2抗烧蚀复合涂层(英文)

为改善碳/碳(C/C)复合材料的抗烧蚀性能,采用包埋技术在C/C复合材料表面制备了碳化硅-硅化铪(SiC-HfSi2)抗烧蚀复合涂层。采用氧乙炔火焰烧蚀试验评价了C/C复合材料样品的抗烧蚀性能。通过扫描电镜观察、能谱分析及X射线衍射分析研究了烧蚀前后C/C复合材料抗烧蚀涂层的表面和断面形貌、元素分布和相组成。结果表明:涂层C/C复合材料在烧蚀后其表面出现了丛生的氧化硅纳米线。同时,与未涂层C/C复合材料相比,SiC-HfSi2涂层使C/C复合材料的质量烧蚀率下降了85.6%。     

CVD沉积工艺对SiC涂层结晶度与耐腐蚀性能的影响

通过化学气相沉积(CVD)SiC涂层来提高SiC_f/SiC复合材料的耐腐蚀性能,本文以CH_3SiCl_3(MTS)为源气体,在反应烧结SiC基体上制备SiC涂层,控制沉积温度、炉压及H_2/MTS摩尔比等工艺参数,通过X射线衍射实验(XRD)得到不同工艺条件下生成的碳化硅涂层的物相组成和结晶度,通过高温水腐蚀实验检测涂层的耐腐蚀性,并利用扫描电子显微镜(SEM)观察腐蚀前后的表面形貌。结果表明:当沉积时间为8 h,沉积温度从1050℃到1250℃,β-SiC涂层表面平整性提高,沉积厚度由12.97μm急剧增加至71.10μm, SiC晶粒尺寸逐渐增大,最终呈金字塔状;碳化硅涂层腐蚀60 d后,表面呈现针状结构,1250℃下沉积的SiC涂层耐腐蚀性能较好;β-SiC涂层的晶粒尺寸随沉积炉压的增大而增大,结晶度随沉积炉压增大而减小,在200 Pa以下,获得的β-SiC晶粒的结晶度最高(81.08%)、晶粒尺寸最小(13.7 nm);随着H_2/MTS摩尔比增加,β-SiC晶粒结晶度迅速下降,当H_2/MTS=6.5时,结晶度最高(95.91%)。     

预加SiC粉的碳热还原法制备SiC-B_4C复合陶瓷粉

为了改善制备SiC-B_4C复合陶瓷的传统工艺流程(B_4C与SiC机械混合后烧结),提高B_4C与SiC在微观尺度上结合的均匀性和紧密性,使其更有利于烧结致密化,从而进一步提高复合陶瓷的综合性能,在碳热还原法制备B_4C的配料中分别添加占总质量1%、2%、3%、4%、5%的SiC粉,干混均匀,再加入5%(w)的水搅拌均匀,然后采用油压千斤顶以20 MPa压力模压成型为15 mm×10 mm的样坯,在80℃干燥10 h后,在1 800℃空气气氛中频感应炉中烧结50 min,最后进行XRD分析和SEM观察。结果表明:采用在碳热还原法制备B_4C的配料中预加SiC粉的方法,成功制备了B_4C分布均匀、SiC与B_4C结合紧密的SiC-B_4C复合陶瓷粉。随着SiC添加量的增多,B_4C衍射峰强度明显增强,B_4C晶粒形貌变得更加规则,且晶粒尺寸有所增大,表明SiC添加量增多促进了B_4C的生成及其晶粒的生长。     

C/C复合材料抗氧化耐高温SiC陶瓷涂层的研究

采用高温反应法和PVD法在SiC工业合成炉内制备了C/C复合材料耐高温抗氧化SiC陶瓷涂层.用XRD、SEM对其物相组成和显微结构进行了表征与分析,讨论了涂层的形成机理,并研究了其高温氧化性能.研究结果表明,所制备的陶瓷涂层主要由α-SiCβ-SiC组成,晶粒发育完整,涂层表面致密、无裂纹,且与碳基体结合紧密,涂层厚度约600μm,涂层抗氧化性良好,在1500℃空气中氧化10h失重约为0.3%.     

碳热还原法低温制备碳化硅微粉

以SiO2为硅源,炭黑为碳源,Fe2 O3为催化剂,采用碳热还原法在氩气保护下制备SiC微粉,研究催化剂含量,合成温度对SiC生成、形貌的影响.实验结果表明:在原料中添加Fe2 O3粉,1350℃保温3h就能产生SiC微粉;由X射线衍射分析显示,在1450℃下保温3h基本上全部转化为晶粒尺寸在50 nm左右SiC微粉;在相同温度下,随着Fe2 O3用量的增加,SiC产率增加.添加Fe2O3能加快反应速度以及提高SiC微粉的生成量.     

C/C复合材料SiC-MoSi2-WSi2抗氧化涂层的制备及性能研究

为提高C/C复合材料的高温抗氧化性能,以聚碳硅烷(PCS)浸渍裂解法和Si,Mo,W粉浆料刷涂反应法在C/C复合材料表面制备SiC-MoSi2-WSi2复合涂层,借助X射线衍射仪、扫描电镜等分析手段,对涂层的微观形貌、组织结构及物相进行分析研究,优化涂层制备工艺,考察了涂层的高温抗氧化性能,分析了抗氧化机理.制备的SiC-MoSi2-WSi2复合涂层厚度200 μm左右,主要由SiC,MoSi2,WSi2构成.1500℃氧化试验结果表明复合涂层的静态氧化失重率较SiC单层涂层降低50％以上,较大地改善了C/C复合材料的抗氧化性能.     

碳/碳复合材料SiC–HfSi_2–TaSi_2抗烧蚀复合涂层

采用包埋技术在碳纤维增强碳(carbon fiber reinforced carbon,C/C)复合材料表面制备了碳化硅-硅化铪-硅化钽(SiC-HfSi2-TaSi2)抗烧蚀复合涂层.采用氧已炔火焰烧蚀试验评价了. C/C复合材料样品的抗烧蚀性能.通过X射线衍射分析、扫描电镜观察及能谱分析研究了SiC-HfSi-TaSi2作为 C/C复合材料抗烧蚀涂层的表面和断面相组成、元素分布及形貌.结果表明:由于烧蚀过程中生成的Hf02,Ta205具有高温稳定性,使得该涂层表现 出良好的抗烧蚀性能,在3 000℃下烧蚀20s后,线烧蚀率为0.009 mm/s,质量烧蚀率为0.003 85 g/s.     

碳纤维增强碳复合材料表面多层复合涂层中SiC和TiC内层的比较(英文)

采用包埋法制备了碳纤维增强碳(carbon fiber reinforced carb on composites,C/C)复合材料表面多层涂层,包括SiC,TiC内层,SiC,TiC中间层以及SiC+TiC复合外层。利用场发射扫描电镜和X射线衍射对其表面和断面的结构进行研究。结果显示:和TiC内层相比较,SiC内层较厚而且致密,具多孔结构且和C/C复合材料结合紧密;TiC内层较薄且和C/C复合材料结合松散。制备的SiC+TiC复合外层由SiC,TiC和Ti3SiC2组成。     

无黏结剂碳/陶复合材料的抗氧化机理

无黏剂C/C复合材料同其他C/C复合材料一样存在抗氧化性能差这一致命的弱点 ,采用防氧化表面涂层不能很好地解决涂层与基体间热膨胀差异所带来的裂纹问题 .通过采用一定比例的生石油焦、B₄C和SiC混合磨粉后 ,加入短碳纤维 ,无需添加黏结剂模压成型 ,而后烧结制得结构密实均匀的碳 /陶复合材料 .在 900～1200℃温度范围内对其抗氧化性能进行测试 ,结果表明该材料具有良好的抗氧化性能。从热力学的角度对其抗氧化机理进行了探讨 .     

抗氧化碳／碳复合材料

详细地叔述了氧化碳/碳材料的制备、性能与应用。分析了抗氧化机制,指出,无论用硼酸盐浸渍还是用SiC涂层防氧化,其基本原理都是氧化后在碳/碳材料表面上形成一层完整的、致密的玻璃膜,这层膜抗挥发温度的高低就限定了它的使用温度。     

碳/碳复合材料表面SiC/c-AlPO_4复合涂层及其抗氧化机制

采用二次包埋法和水热电泳沉积法相结合的工艺在碳纤维增强碳复合材料表面制得SiC/方石英型磷酸铝(cristobalite aluminum phosphate,c-AlPO4)复合涂层。借助X射线衍射仪和扫描电镜对复合涂层的晶相组成和显微结构进行了表征。研究了复合涂层的高温氧化性能,讨论了复合涂层氧化、失效的机理。结果表明:复合涂层具有双层结构,包埋的SiC内层主要由α-SiC,β-SiC和少量的游离硅组成,外层由c-AlPO4颗粒构成,内外层结合紧密。复合涂层在1300～1500℃范围内具有良好的抗氧化性能,其氧化激活能为117.2kJ/mol,氧化过程主要受氧在c-AlPO4层中的体扩散速率所控制;氧化气体逸出留下的孔洞是复合涂层防氧化失效的主要原因。     

Fabrication of New Cemented Carbide Containing Diamond Coated with Nanometer-Sized SiC Particles

A simple process for depositing a coating of silicon carbide (SiC) crystallites ∼10 nm in size onto diamond particles has been developed. SiO powders react with diamond in a vacuum at 1350°C to form a uniform β-SiC polycrystalline layer ∼60 nm thick. The SiC coating improves the oxidation resistance of the diamond. A cemented carbide material containing 20-vol%-SiC-coated diamond particles was sintered to a relative density of 99.5% by pulsed-electric-current sintering. A Vickers hardness and indentation fracture toughness of 15 GPa and 16.3 MPa·m^1/2, respectively, were obtained. This toughness is two times higher than that of cemented carbide containing no particles. The higher toughness is attributed to deflection and blockage of crack propagation by the diamond particles.     

多孔碳柱撑膨润土的制备与表征

用十六烷基三甲基溴化铵和苄基三甲基氯化铵改性膨润土制备了多孔碳柱撑膨润土.用Fourier变换红外光谱仪、扫描电子显微镜和氮气吸附-脱附、热分析系统地研究了有机改性剂对多孔材料性能的影响.结果表明:膨润土微粒与有机改性剂以共价键和离子嵌入2种形式结合;多孔碳柱撑膨润土的微观形貌呈针片状,最可几孔径分布大约在1.7nm;多孔材料的主要结构是由碳化的大粒子柱撑而构建的二维孔径,烧结后的有机黏土热稳定性大大提高.     

Carbon nanotubes coated with diamond nanocrystals and silicon carbide by hot-filament chemical vapor deposition below 200 °C substrate temperature

Multi-walled carbon nanotubes (MWCNTs) dispersed onto a silicon substrate have been coated with diamond nanocrystals (DNC) and silicon carbide (SiC) from solid carbon and silicon sources exposed to H₂ activated by hot filament chemical vapor deposition (HFCVD) at around 190 °C substrate temperature. MWCNT coating by DNC initiates during filament carburization process at 80 °C substrate temperature under conventional HFCVD conditions. The hybrid nanocarbon material was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. The structure of the MWCNTs is preserved during coating and the smooth DNC/SiC coating is highly conformal. The average grain size is below 10 nm. The growth mechanism of DNC and SiC onto MWCNT surface is discussed.     

Molten salt synthesis and characterization of SiC coated carbon black particles for refractory castable applications

Silicon carbide (SiC) coatings were prepared on carbon black (CB) particles after 6 h at 1100 °C by a molten salt synthesis (MSS) technique. By controlling the Si to CB ratio (Si/C) in the initial batch mixture, the SiC coating thickness could be readily tailored to meet practical requirements in real castable systems. True densities of CB particles after SiC coating increased with Si/C. The zeta potential values indicated that their dispersivity was improved evidently over a wide range of pH. At a given shear rate, the apparent viscosity of a water suspension containing SiC-coated CB was significantly lower than that of a water suspension containing as-received uncoated CB, indicating the improved flowability of SiC-coated CB in water. The improvements in both the water-dispersivity and flowability of SiC coated CB particles would make them a promising candidate carbon material for future castable applications.     

Deposition Rate,Texture, and Mechanical Properties of SiC Coatings Produced by Chemical Vapor Deposition at Different Temperatures

Silicon carbide (SiC) coatings were produced on carbon/carbon (C/C) composites substrates using chemical vapor deposition (CVD) at different temperatures (1100°C, 1200°C, and 1300°C). The deposition rate was found to increase with deposition temperature from 1100°C to 1200°C. From 1200°C to 1300°C, the deposition rate decreased. SiC coating produced at 1200°C exhibited a strong (111) texture compared with the coatings produced at other temperatures. Both hardness and Young's modulus were also found to be higher in the coating produced at 1200°C. The variation in mechanical properties with the increase in temperature from 1100°C to 1300°C showed a direct correlation with the change in deposition rate and (111) texture. Microstructure analysis shows that the change in CVD temperature leads to the change in grain size, crystallinity, and density of stacking faults of SiC coatings, which appears to have no significant effect on mechanical properties of SiC compared with the texture observed in SiC coating. For the coating deposited at 1200°C, both the hardness and Young's modulus increased gradually from the substrate/coating interface to the top surface. The nonuniformity of mechanical properties along the cross‐section of the coating is attributed to the nonuniform microstructure.     

A microstructural study of carbon–carbon composites impregnated with SiC filaments

Porous multidirectional carbon/carbon composite obtained by pulse chemical vapour infiltration (PCVI) was impregnated with silicon carbide (SiC) derived from pyrolysis of polymethylsiloxane resin (PMS). The impregnation process was made to improve oxidation resistance and mechanical properties of MD C/C composite. The resin was used as a source of silicon carbide component of the composite forming after heat treatment above 1000 °C. During this process SiC thin filaments were formed inside the porous carbon phase. The aim of this work was to investigate the structure and microstructure of the constituents of carbon composite obtained after pyrolysis of SiC PMS precursor. Microscopic observations revealed that during careful heat treatment of crosslinked polymethylsiloxane resin up to 1700 °C, the filaments (diameter 200–400 nm) crystallized within porous carbon phase. The filaments were randomly oriented on the composite surface and inside the pores. FTIR spectra and XRD analysis of the modified C/C composite showed that filaments had silicon carbide structure with the crystallite size of silicon carbide phase of about 45 nm. The Raman spectra revealed that the composite contains two carbon components distinctly differing in their structural order, and SiC filaments present nanocrystalline structure.     

A focused review on the tribological behavior of C/SiC composites: Present status and future prospects

Silicon carbide-based ceramic matrix composites have received extensive attention in recent years. Many excellent reviews have reported on the tribological behavior of carbon fiber-reinforced carbon and silicon carbide dual matrix (C/C-SiC) composites. However, a systematic overview of the tribological properties of carbon fiber-reinforced silicon carbide (C/SiC) composites does not exist. This review focuses on C/SiC composites and summarizes the key factors, including internal factors (constituent content, graphitization process, material structure and fiber direction), and various test conditions (pressure and speed, dry and wet, temperature, and counterparts) that affect their tribological behavior. Their wear mechanisms under different conditions are elaborated. Finally, some potential future development directions for improving the performance of C/SiC composites are proposed to provide high-quality ceramic matrix composites for engineering applications. These directions include structural modification, matrix modification, coating technology, laser surface texturing, and material genome method.     

Strengthening/toughening of 2D C/SiC composites by coating

SiC and SiC_w/SiC coatings were prepared on two-dimensional carbon fiber reinforced silicon carbide ceramic matrix composites (2D C/SiC), and strengthening/toughening of the composite by the coatings was investigated. After coating, the density of the C/SiC composites was increased effectively and the mechanical properties were improved significantly. Compared with SiC coating, SiC_w/SiC coating showed the more significant effect on strength/toughness of the composites. Coatings had two effects: surface strengthening and matrix strengthening. The latter was the dominant effect. The surface strengthening can increase the crack initiation stress, while the matrix strengthening can enhance the crack propagation resistance. The former effect increased the strength and the latter effect increased the toughness.