三维网络SiC多孔陶瓷增强铝基复合材料的制备

以中间相沥青添加质量分数为50%的Si粉制备的炭泡沫预制体为坯体,在高温感应烧结炉中结合反应烧结工艺制备了SiC多孔陶瓷预制体.利用挤压铸造工艺制备了SiC多孔陶瓷增强铝基复合材料.采用扫描电子显微镜(SEM)观察了SiC多孔陶瓷骨架及复合材料的微观形貌和界面结构,通过X射线衍射分析仪(XRD)对多孔陶瓷预制体物相组成进行了分析.利用阿基米德排水法,测试了多孔陶瓷的孔隙率和复合材料的密度.结果表明:添加Si的质量分数为50%的炭泡沫预制体反应烧结后获得的SiC多孔陶瓷具有三维连续通孔结构,孔筋致密并且具有较高的开口孔隙率.通过挤压铸造工艺制备的SiC多孔陶瓷增强铝基复合材料界面结合良好,无明显缺陷.     

多孔SiC陶瓷增强金属基复合材料的制备

采用纸质材料制成三维管状模型，经过纸质模型碳化、反应性渗硅处理获得多孔SiC陶瓷预制体，选择铸造性能好、成形缺陷小的铸铁作为金属基体，采用铸渗法制备了SiC陶瓷增强金属基复合材料，通过XRD，SEM等分析手段研究了多孔SiC陶瓷和复合材料的显微组织和界面结构。研究表明，纸质模型800℃温度碳化，反应性渗硅温度1600℃时制备的多孔SiC陶瓷预制体三维结构稳定，烧结后变形小，微观组织结合紧密；通过铸渗法制备的SiC陶瓷增强金属基复合材料界面结合良好，无明显缺陷。该方法中增强相结构可设计性好，铸渗法制备多孔陶瓷金属基复合材料质量高，为多孔陶瓷增强金属基复合材料的获得提供了试验新方法。     

Ni基高温钎料连接SiC陶瓷的微观结构和力学性能

采用低成本的Ni基高温钎料对SiC陶瓷进行了钎焊连接，通过扫描电镜、能谱分析、透射电镜等测试手段分析了接头的微观结构和物相组成，系统研究了不同钎焊温度和保温时间对SiC/SiC接头力学性能及微观结构的影响规律，分析了不同钎焊工艺参数下制备的SiC/SiC接头断口形貌，阐明了接头宏观力学性能与微观结构之间的对应关系。最后，评价了SiC/SiC接头的高温力学性能。结果表明，SiC/SiC接头由反应区、中心区和基体区3个区域组成，其中反应区主由Ni₂Si和不同数量的石墨组成；而中心区主要由复杂碳化物Ni₃Mo₃C和Ni₂Si组成。提高钎焊温度和延长保温时间石墨能够使SiC/SiC接头的反应区厚度增加，生成石墨相的数量也逐渐增多并发生团簇聚集的现象，显著影响了接头的抗弯强度。在1 300℃，40 min条件下，反应区的厚度和石墨的形成量是适宜的，SiC/SiC接头的室温四点抗弯强度最大，达到179 MPa±7 MPa。同时，该接头还具有良好的高温稳定性，在700℃高温下仍能有97.2%的强度保持率，在高温环...     

挤出成形法制备多孔SiC陶瓷工艺研究

设计了不同孔径、不同形状的多孔蜂窝结构,对挤出浆料组成配方和挤出成形工艺进行了优化,采用挤出成形法制备了蜂窝多孔SiC陶瓷坯体,并通过反应烧结制备了蜂窝多孔SiC陶瓷,研究了挤出压力、速率等工艺参数对蜂窝多孔SiC陶瓷坯体质量的影响,以及反应烧结温度、排硅时间等对蜂窝多孔SiC陶瓷密度、强度等性能的影响。结果表明:合适的挤出压力、挤出速率有助于确保多孔陶瓷坯体的成形和具有一定的强度;反应烧结后排硅时间在0.5h时多孔SiC陶瓷三点弯曲强度最高,为25.67MPa,制备的多孔SiC陶瓷/耐热钢基复合材料陶瓷分布均匀,界面结合良好。     

SiC改性碳复合材料的微观结构分析和力学性能研究

利用SiC与碳基材料复合，采用原位合成技术制备了一种新型碳陶瓷复合材料。采用XRD和SEM技术分别表征材料的相组成和微观形貌结构，并利用万能材料试验机测试了复合材料的抗压和抗折性能。XRD测试结果表明，SiC改性碳陶瓷复合材料中没有新相产生。由SEM照片分析可知，SiC的掺杂破坏了石墨原有的层片状结构，并在碳石墨材料中观察到颗粒状晶体，随着SiC掺量的增加，散乱分布的晶粒有聚集长大的趋势，造成碳陶瓷复合材料结构的进一步破坏。力学性能测试结果表明，当掺入10％SIC（质量分数）时，材料的抗折强度最大，为58．8MPa；而在SiC掺量为5％（质量分数），其抗压强度达到最大，为157．4MPa。     

多孔SiC陶瓷增强金属基复合材料的制备

采用纸质材料制成三维管状模型,经过纸质模型碳化、反应性渗硅处理获得多孔SiC陶瓷预制体,选择铸造性能好、成形缺陷小的铸铁作为金属基体,采用铸渗法制备了SiC陶瓷增强金属基复合材料,通过XRD,SEM等分析手段研究了多孔SiC陶瓷和复合材料的显微组织和界面结构.研究表明,纸质模型800C温度碳化,反应性渗硅温度1600℃时制备的多孔SiC陶瓷预制体三维结构稳定,烧结后变形小,微观组织结合紧密;通过铸渗法制备的SiC陶瓷增强金属基复合材料界面结合良好,无明显缺陷.该方法中增强相结构可设计性好,铸渗法制备多孔陶瓷金属基复合材料质量高,为多孔陶瓷增强金属基复合材料的获得提供了试验新方法.     

SiC多孔陶瓷的低温制备与表征

以聚碳硅烷为粘接剂，SiC粉末为骨料，经模压成型、惰性气氛保护下于1000℃裂解低温制得SiC多孔陶瓷。考察了聚碳硅烷含量、SiC粉末粒径、模压压力、造孔剂碳含量等参数对多孔陶瓷孔隙率、弯曲强度、孔结构的影响。结果表明，随着聚碳硅烷含量和模压压力的增加，SiC多孔陶瓷的开口孔隙率下降，弯曲强度升高；随着造孔剂碳含量的增加，多孔陶瓷的孔隙率由53．05％升高至58．6％，抗弯曲强度迅速由7．88MPa下降到1．08MPa。随着模压压力的升高，多孔陶瓷的平均孔径下降；随着SiC粉末粒径的增加，平均孔径增大。     

Y2O3对反应烧结Si3N4/SiC复相陶瓷组织和性能的影响

以低压铸造用升液管为研究目的,以Y2O3-Al2O3-Fe2O3为复合烧结助剂,磨切单晶硅废料Si粉和SiC为主料,反应烧结法制备Si3N4/SiC复相陶瓷。研究了Y2O3含量对复合材料结构和力学性能的影响,采用XRD、SEM对复合材料的相组成、微观形貌进行分析。结果表明,反应烧结后试样生成Si3N4结合SiC晶粒为主相的烧结体,并含有少量Sialon晶须及未反应的Si。Y2O3含量对复相陶瓷力学性能影响很大,在分析稀土Y2O3作用机理的基础上,得到2.5%Y2O3优化试样的力学性能优良,相对密度达到88%,维氏硬度达到1.1 GPa,常温抗弯强度50 MPa。     

工艺参数对SiC陶瓷热压反应连接强度的影响

采用Ag粉和Ti粉作为焊料，对再结晶SiC陶瓷进行热压反应连接。研究了2种工艺，其中工艺1与传统的扩散焊工艺相似，即分别在不同的焊接温度下保温一定的时间；而工艺2则是首先在某一较高温度下进行短时间的保温，以利于Ti与SiC母材发生适度的界面反应，促进界面结合，同时液相银的出现将显著缓解焊接应力，随后在另一相对较低的温度下保温较长时间，以利于Ag—Ti金属间化合物的形成，有利于提高接头的焊接强度和工作温度。结果表明，采用工艺2获得的接头抗弯强度较高，达到SiC陶瓷母材强度的73．4％。微观结构研究表明，在界面处生成了反应层，焊料产物主要由两种相相间组成。EDX分析结果表明，界面处发生了元素的互扩散。     

放电等离子体烧结TiC-SiC复合陶瓷的制备与表征

通过放电等离子体烧结(SPS)工艺制备TiC-SiC复合陶瓷,利用XRD、SEM、压痕法等测试手段表征烧结后复合陶瓷的相组成、微观形貌、力学性能。从TiC晶粒大小、SiC的分布状态、样品的维氏硬度和断裂韧性等方面研究了亚微米级SiC对TiC陶瓷基体显微结构和力学性能的影响。结果表明,SiC的添加提高了TiC基体的断裂韧性,细化了TiC晶粒。利用弥散强化和残余应力解释了断裂韧性改善的原因。     

Effect of Steam Activation on Development of Light Weight Biomorphic Porous SiC from Pine Wood Precursor

Biomorphic SiC materials with tailor-made microstructure and properties similar to ceramic materials manufactured by conventional method are a new class of materials derived from natural biopolymeric cellulose templates (wood). Porous silicon carbide (SiC) ceramics with wood-like microstructure have been prepared by carbothermal reduction of charcoal/silica composites at 1300-1600 °C in inert Ar atmosphere. The C/SiO₂ composites were fabricated by infiltrating silica sol into porous activated biocarbon template. Silica in the charcoal/silica composite, preferentially in the cellular pores, was found to get transformed in forms of fibers and rods due to shrinkage during drying. The changes in the morphology of resulting porous SiC ceramics after heat treatment to 1600 °C, as well as the conversion mechanism of wood to activated carbon and then to porous SiC ceramic have been investigated using scanning electron microscope, x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. Activation of carbon prior to silica infiltration has been found to enhance conversion of charcoal to SiC. The pore structure is found to be uniform in these materials than in those made from as-such charcoal/silica composites. This provides a low-cost and eco-friendly route to advanced ceramic materials, with near-net shape potential.     

纳米SiC颗粒增强反应烧结碳化硼复合材料的研究

采用真空熔渗法,通过对B4C-C素坯于1550 ℃渗Si,得到了较致密的反应结合碳化硼陶瓷复合材料。通过生成SiC纳米颗粒对材料进行强化,并探讨了纳米SiC颗粒对材料组织与性能的影响及其强韧化机理。实验表明,材料包括B4C、Si、SiC和B12(C,Si,B)3四相。结果表明,选取酚醛树脂作为外加碳源,可在材料中成功引入细小的SiC纳米颗粒,使复合材料的抗折强度、断裂韧性和维氏硬度较以炭黑为外加碳源的材料,分别增加了35 %、36 %和15 %,分别高达442 MPa、4.9 MPa?m1/2和23 GPa。     

反应烧结SiC制备SiC/B4C复合材料的研究

基于反应烧结SiC制备出相对密度较高的SiC/B4C复合材料,并探讨原料中C含量对SiC/B4C复合材料物相、显微结构、体积密度、力学性能的影响。结果表明,SiC/B4C复合材料的相组成为B4C、SiC、Si、B13C2和B12.97Si0.03C2。SiC/B4C复合材料的显微组织为:SiC相和B4C相均匀分布,游离Si填充在B4C相和SiC相的空隙处,且形成了连续相。随着原料中C含量的增加,复合材料的力学性能整体呈现先增加后降低的趋势。原料中C最佳添加量为10%(质量分数),对应SiC/B4C复合材料的维氏硬度、抗弯强度和断裂韧性分别为24.4GPa、361.3MPa和4.41MPa·m1/2,复合材料开口气孔率和体积密度分别为0.19%和2.58g/cm3。     

Microstructure,sintering behavior and mechanical properties of SiC/MoSi2 composites by spark plasma sintering

SiC/MoSi₂ composites were synthesized at different temperatures by spark plasma sintering using Mo, Si and SiC powders as raw materials. The phase composition, microstructure and mechanical properties of the as-prepared composites were investigated and the sintering behavior was also discussed. Results show that SiC/MoSi₂ composites are composed of MoSi₂, SiC and trace amount of Mo_4.8Si₃C_0.6 phase and exhibit a fine-grain texture. During the synthesis process, there was an evolution from solid phase sintering to liquid phase sintering. When sintered at 1600 °C, the SiC/MoSi₂ composites present the most favorable mechanical properties, the Vickers hardness, bending strength and fracture toughness are 13.4 GPa, 674 MPa and 5.1 MPa·m^1/2, respectively, higher 44%, 171%, 82% than those of monolithic MoSi₂. SiC can withstand the applied stress as hard phase and retard the rapid propagation of cracks as second phase, which are beneficial to the improved mechanical properties of SiC/MoSi₂ composites.     

Preparation and characterization of biomorphic SiC hollow fibers from wood by chemical vapor infiltration

Biomorphic SiC hollow fibers were prepared by the reactive infiltration of SiO vapor into basswood-derived charcoal. Gaseous SiO was produced from a SiO₂/Si powder mixture in Ar at elevated temperatures. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform-infrared spectroscopy were employed to characterize the structural morphology and phase compositions of the final products. The results show that the tubular cells in bulk charcoal are converted into lots of SiC hollow fibers with pore diameters of 10–50 μm and lengths ranging from hundreds of μm to several mm. Resulting SiC hollow fibers consist of β-SiC with a minute amount of α-SiC. The formation mechanism of SiC hollow fibers is based on the gas–solid reaction between SiO and carbon.     

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.     

Synthesis of nanostructured SiC coatings on carbon fibres by in situ reaction sintering with milled powders

A homogeneous and continuous nanostructured SiC coating on the surfaces of T700 and M40 carbon fibres was synthesized by in situ reaction sintering at 1450 °C with the milled Si and C powders, and the coating was characterized. The results show that the slurry is easier to stick to the surface of M40 carbon fibres than that of T700 carbon fibres. A homogeneous, continuous and crack-free nanostructured SiC coating is formed on the surface of these two kinds of carbon fibres. The SiC coating is composed of huge amounts of nanometric SiC crystals. Coatings with thickness of about 30 nm and 150 nm were fabricated. Carbon fibres with SiC coating whose thickness is about 30 nm display good flexibility.     

高纯度Ti3SiC2粉体的制备及真空热处理

以3Ti/S i/2C/0.2A l粉体为原料通过机械合金化制备了Ti3S iC2粉体,用X射线衍射仪和扫描电镜对机械合金化粉体和热处理粉体进行相分析和颗粒形貌观察,研究了真空热处理温度对机械合金化制备Ti3S iC2粉体纯度的影响。结果表明,3Ti/S i/2C粉体球磨10 h可获得由TiC、Ti3S iC2、TiS i2组成的混合粉体,粉体中的Ti3S iC2含量最高可达到83wt%。在热处理温度为700~1000℃内Ti3S iC2粉末粉体含量随温度的提高而增加,当热处理温度为1000℃时,其含量可达到98wt%以上。     

Si粉粒径及其添加量对SiC陶瓷材料结构和性能的影响

将平均粒径为75 μm和48 μm、质量分数为0%~8%的Si粉分别添加到SiC陶瓷材料中,在1550℃下保温3 h烧成,研究Si粉粒径及其添加量对SiC陶瓷材料烧结性能、力学性能和显微结构的影响。结果表明:添加不同粒径及质量分数的Si粉可改善SiC陶瓷材料的显微结构,提高其烧结性能和力学性能;在一定范围内,较小粒径的Si粉更有利于形成均匀、致密的SiC烧结体,大幅提升SiC陶瓷材料的性能;当Si粉粒径为48 μm且添加的质量分数为4%时,SiC陶瓷材料的烧结性能和力学性能较优,其体积密度和显气孔率分别为2.58 g/cm3和13.5%,抗弯强度和洛氏硬度分别为25 MPa和115 HRB。