聚合物先驱体组分对SiC/SiBCN复合材料性能的影响

以SiC纤维为增强相,SiBCN复相陶瓷先驱体为浸渍剂,采用聚合物先驱体浸渍裂解工艺制备了SiC/SiBCN复合材料。采用SEM和力学性能测试对SiC/SiBCN复合材料氧化前后组分、形貌及力学行为进行了分析。试验表明,随着SiBCN复相陶瓷先驱体中聚硼氮烷(PBN)含量的增加,先驱体陶瓷产率先增加后降低,SiC/SiBCN复合材料1000℃/20 h氧化后的弯曲强度保留率亦先增加后降低。这主要归因于SiBCN复相陶瓷先驱体中PBN含量的增加有利于先驱体分子交联程度增加,更容易形成稳定的三维网络结构。此外,材料孔隙率以及SiBCN复相陶瓷的氧化行为也成为影响SiC/SiBCN复合材料氧化稳定性的重要因素。     

高温处理对不同浆料制备C/SiC复合材料的影响

以先驱体浸渍裂解(PIP)工艺制备的C/SiC复合材料为研究对象,考察了聚碳硅烷/二甲苯(PCS/Xylene)和聚碳硅烷/二甲苯/碳化硅粉(PCS/Xylene/SiC)两种浆料对C/SiC材料耐高温性能的影响.研究发现:在1600 ℃惰性气氛保护下高温处理1 h后,PCS/xylene/SiC制备的材料失重较大,达4.67%.弯曲强度在高温处理前后的保留率较高,高温处理后其强度达464.1 MPa,但模量下降明显.高温处理使C/SiC材料的增韧机制发生改变,PCS/Xylene中添加SiC改变了材料的界面结构.结果表明:两种不同的浸渍浆料对C/SiC材料的耐高温性能有着较明显的影响.     

多孔C泡沫预制体液相渗硅制备C/SiC复合材料研究

以多孔C泡沫为预制体,利用液相渗Si工艺制备了C/SiC复合材料。采用酚醛树脂浸渍-裂解工艺对C泡沫预制体的孔隙率进行调整,考察浸渍-裂解周期对C泡沫预制体孔隙率的影响,研究了C泡沫预制体孔隙率对C/SiC复合材料密度、力学性能、组成和结构的影响。结果表明:预制体孔隙率为72%时制备的C/SiC复合材料性能较好,其密度为2.58g/cm3、弹性模量为81.39GPa,抗弯曲强度为83.88MPa;随着预制体孔隙率的降低,复合材料的密度、弹性模量和抗弯曲强度不断降低,预制体孔隙率的降低影响液相Si充分扩散与C反应,造成复合材料内部存在大量闭孔,这是导致C/SiC复合材料性能下降的主要原因。     

含高体积分数SiC_p的Al复合材料微观组织及弯曲性能

利用无压浸渗法制备高体积分数SiC的SiC_p/Al复合材料.采用XRD和SEM对复合材料的相组成、微观组织及断口形貌进行分析,研究颗粒粒径分布和基体合金成分对复合材料抗弯性能的影响.结果表明:以Al-10Si-8Mg(质量分数,%)合金为基体制备的复合材料组织均匀,致密度好,无明显气孔缺陷;界面反应产物为Mg2Si、MgAl_2O_4和Fe,其弯曲强度高于以Al-10Si合金为基体制备的复合材料的弯曲强度;SiC_p/Al复合材料的弯曲强度随着SiC颗粒粒径的增大而减小;复合材料整体上表现出脆性断裂的特征.     

碳纤维CVD SiC涂层对C/SiC复合材料力学性能的影响

采用CVD PIP工艺制备了SiC涂层碳纤维增强SiC复合材料(C/SiC),研究了碳纤维表面CVD SiC涂层的形貌以及涂层对C/SiC复合材料力学性能的影响.结果表明CVD SiC涂层处理可以填补纤维表面上的沟槽和缺陷,使纤维表面变得光滑,从而使C/SiC复合材料的力学性能有很大提高,碳纤维经过CVD SiC 1 h涂层处理的C/SiC复合材料的力学性能最好,弯曲强度达到511.5 MPa,断裂韧性达到20.8 MPa·m1/2.     

PIP法制备陶瓷基复合材料构件的弯曲性能研究

采用先驱体转化工艺(PIP)制备三维炭纤维增强碳化硅陶瓷基复合材料(3D-Cf/SiC)构件。通过三点弯曲强度方法分析构件材料的弯曲性能及破坏规律。研究表明:采用三维炭纤维编织的陶瓷基复合材料构件,其复合材料基体的主要成分为β-SiC,材料具有较高的弯曲性能,可达511MPa,构件材料与采用同种PIP工艺制备的3D-Cf/SiC陶瓷基复合材料相比较,强度降低26.4%,这可能是由制备的构件其致密度较低以及后续加工等因素所致。3D-Cf/SiC陶瓷基复合材料在弯曲断裂过程,材料纤维与纤维束被大量拔出,表现出类似金属的较好假塑性断裂特征。     

硅树脂先驱体转化制备2DCf/Si-O-C

以二维碳纤维布、硅树脂先驱体、SiC微粉和乙醇溶剂为原料,采用PIP工艺制备了2D Cf/Si-O-C材料,考察了浆料配比对材料力学性能和抗氧化性能的影响.结果表明:硅树脂/乙醇/SiC配比为3∶1.2∶1时所制备材料的力学性能较好,其弯曲强度和断裂韧性分别达到249 MPa和12.7 MPa·m1/2.与力学性能的变化趋势不同,随着浆料中SiC含量的增加,材料的抗氧化性能随之提高,硅树脂/乙醇/SiC配比为3∶1.2∶4时所制备材料在1300℃氧化10 min后,弯曲强度和断裂韧性保留率分别达到了76.3%和83.9%,较未添加SiC微粉的2D Cf/Si-O-C材料有明显提高.     

基体对PIP法制备2D Cf/SiC材料抗氧化性能的影响

以3k JC1#纤维布为增强体,以聚碳硅烷为先驱体,采用先驱体转化工艺制备了2D Cf/SiC复合材料,考察了基体结构对材料抗氧化性能的影响.结果表明,先驱体转化2D Cf/SiC复合材料的抗氧化性能主要与材料基体中的游离碳含量及孔隙率有关,基体中游离碳含量和孔隙率越高,材料的抗氧化性能越差.通过减少基体中的孔隙率和游离碳含量,可以制备抗氧化性能较好的2D Cf/SiC复合材料,在1300℃,马弗炉中氧化20 min后,材料的失重率仅为2.2%,弯曲强度和断裂韧性保留率达到83.6%和80.9%.     

等离子喷涂制备C/C复合材料SiC涂层的驻点烧蚀性能

目的在C/C复合材料表面制备SiC涂层,提高C/C复合材料抗烧蚀性能。方法采用真空等离子喷涂技术在C/C复合材料表面制备纯Si涂层,在惰性气氛保护下对涂层高温热处理,纯Si涂层与C元素在高温下反应,原位生成SiC涂层。利用电弧加热器在不同烧蚀温度下,分别考核涂层的驻点烧蚀性能,并采用OM、SEM、EDS和XRD等对烧蚀前后的微观形貌和物相成分进行分析。结果在C/C复合材料表面制备了致密的SiC涂层,涂层中没有明显的裂纹存在,并在涂层下方产生较深的渗透区域,深度超过涂层厚度。制备的SiC涂层在1400℃下烧蚀50 s,涂层完整,具有良好的驻点烧蚀性能;在1600℃和1650℃下烧蚀50 s,涂层部分剥落,C/C复合材料基体产生烧蚀。结论 SiC涂层在高温下氧化成Si O2玻璃态膜,并覆盖在C/C复合材料表面,对基体具有良好的保护作用。随着烧蚀温度的提高,在超音速气流的冲刷下,由于热膨胀系数不匹配和SiC主动氧化的原因,涂层在烧蚀面边缘出现剥落,且剥落现象越来越严重,涂层失去对C/C基体的保护作用,烧蚀性能下降。     

工艺对C/SiC复合材料结构与性能的影响

介绍一种化学气相渗透与先驱体浸渍裂解联用(CVI-PIP)的工艺制备碳毡增强SiC复合材料,采用SEM分析复合材料的显微结构,采用三点弯曲法测试复合材料的力学性能,结果显示在复合材料致密化过程早期,CVI工艺致密化效率明显高于PIP工艺;与完全采用PIP工艺制备C/SiC复合材料相比,采用CVI-PIP工艺可提高复合材料的致密化效率和致密化程度,复合材料残留孔隙率从18.86%下降到5.45%;相应的,C/SiC复合材料的抗弯强度与弹性模量分别从66.43 MPa和38.43 GPa增加到112.16 MPa和68.49 GPa;采用CVI-PIP联用工艺同时能够增加复合材料与其表面CVD涂层的结合性能.     

Blast and tensile properties of tantalum/niobium lined SiC/SiC composite tubes for nuclear cladding

The mechanical performances such as tensile strength and blast property of metal lined SiC/SiC composite cladding tubes were investigated. Nb or Ta was selected as liner material, and the SiC/SiC composite layer was fabricated by winding and different precursor impregnation and pyrolysis (PIP) processes. The tensile strengths of different tube samples were measured at room temperature (RT) and 1200 °C, respectively. The blast property was investigated through the maximum water pressure of tubes. And the fracture microstructures were observed by SEM. The highest tensile strength at RT was 150.7 MPa. The blast strength was enhanced with the PIP process increasing from 1 to 4 cycles and the tube of 4 PIP cycles had the highest water pressure of 34.7 MPa. Compared with the metal tubes, the multi-layer structure improved tensile and blast properties significantly. The different processes such as PIP cycles and pyrolytic carbon (PyC) coating were important factors to enhance the mechanical performances of SiC/SiC-based tubes. However, the retention rate of tensile strength was only 18.5% at 1200 °C.     

ZrC-HfC-TaC改性C/SiC复合材料的循环氧化烧蚀行为

难熔金属碳化物改性是提升陶瓷基复合材料抗氧化性能的有效途径。然而,ZrC-HfC-TaC改性对循环氧化烧蚀性能的影响却鲜有报道。利用前驱体浸渍裂解结合化学气相沉积工艺构筑了ZrC-HfC-TaC改性C/SiC复合材料,剖析了1600 ℃/5 h循环静态氧化后材料的力学强度、化学组成以及微观结构的变化,根据表征结果提出了改性后材料的抗氧化机理,并利用1700 ℃/4000 s循环氧乙块焰烧蚀试验验证了ZrC-HfC-TaC改性对提升循环氧化烧蚀性能的有效性。研究表明,经过ZrC-HfC-TaC改性的C/SiC复合材料具备优异的高温循环氧化烧蚀性能。     

Degradation of strength properties and its fracture behaviour of TiB2-TiC-based composite ceramic cutting tool materials at the high temperature

Strength retention is important for tool materials at high temperature because cutting temperature in machining is ranged from room temperature to 1000 °C. A study examining the strength properties and fracture behaviour of TiB₂-TiC-based composite ceramic cutting tool materials is presented at different temperatures. MoSi₂ and SiC additives are considered to investigate their effects on the density, microstructure, strength and failure mechanism of composites. It is found that the addition of SiC contributed more to the high-temperature strength of composites than MoSi₂, but it did not improve the room-temperature strength, despite grain refinement. The TBAVS8 composite has a flexural strength of 800 MPa at room temperature and can retain 75% at 900 °C. At room temperature, the fracture behaviour of composites was dominated by the strong bonding of the Ni binder phase. At high temperatures, the softer Ni binder phase was pinned, and its sliding was inhibited by SiC particles, which decelerated the strength degradation.     

Glass coating for SiCf/SiC composites for high-temperature application

This work reports on the fabrication of a self-healing, oxidation-resistant glass coating for SiC_f/SiC composites. The glass-coating material is a thermally stable boro-silicate glass with excellent wetting properties and viscosity.Some glass-coated composites were prepared by a simple and low-cost slurry technique, then treated in air for 100 h at 1200°C. Three-point bending tests were performed on the glass-coated composites after the thermal treatment, and the results were compared with the bending strength of the uncoated SiC_f/SiC before and after the same thermal treatment. The mechanical behavior of the glass-coated composite remained almost virtually unaffected after being heated at 1200°C in air for 100 h.     

Effect of loading rate and temperature on monotonic tensile behavior in an enhanced SiC/SiC composite

Tensile behavior in an enhanced SiC/SiC composite has been studied in air at 1200–1400 °C with different loading rates. Tensile strength and failure strain increase with increasing temperature from room temperature to 1200 °C. The glassy phase in the matrix is effective to protect the composite from oxidation.     

Oxidation of SiOC/MoSi2/SiC Composites Prepared by Polymer Pyrolysis

From the pre-ceramic polymer of polymethylsiloxane (PMS) and powders of MoSi₂, SiC and Si, new ceramic composites that consisted primarily of an amorphous SiOC matrix containing dispersed particles of MoSi₂ and SiC were synthesized. The composites displayed superior oxidation resistance at both high and low temperatures by forming SiO₂ on the surface. The thin, amorphous SiO₂ layer that formed initially gradually to crystallized during oxidation between 1000 and 1300°C. An outer highly porous and an inner superficial SiO₂ layer that formed from the initial stage of oxidation between 400 and 500°C protected the composites from pesting.     

Microstructures and Properties of the C/Zr-O-Si-C Composites Fabricated by Polymer Infiltration and Pyrolysis

A way to improve the ablation properties of the C/SiC composites in an oxyacetylene torch environment was investigated by the precursor infiltration and pyrolysis route using three organic precursors (zirconium butoxide, polycarbosilane, and divinylbenzene). The ceramic matrix derived from the precursors at 1200 °C was mainly a mixture of SiC, ZrO₂, and C. After annealing at 1600 °C for 1 h, ZrO₂ partly transformed to ZrC because of the carbothermic reductions and completely transformed to ZrC at 1800 °C in 1 h. The mechanical properties of the composites decreased with increasing temperature, while the ablation resistance increased due to the increasing content of ZrC. Compared with C/SiC composites, the ablation resistance of the C/Zr-O-Si-C composites overwhelms because of the oxide films which formed on the ablation surfaces. And, the films were composed of two layers: the porous surface layer (the mixture of ZrO₂ and SiO₂) and the dense underlayer (SiO₂).     

ZrB₂含量对Nb-Mo-ZrB₂复合材料氧化行为的影响

利用热压烧结法,在2400℃烧结温度下,制备了NbMo固溶体（此后记作(Nb,Mo)ss）基陶瓷颗粒增强复合材料。其中,ZrB2陶瓷增强相的体积分数分别为15%,30%,45%和60%。本文研究了在800℃,1000℃和1200℃下,ZrB2含量对复合材料抗氧化性和氧化产物演变的作用。试验结果表明,氧化温度和ZrB2含量均对复合材料的氧化行为有影响。从氧化速率常数角度讲,ZrB2-(Nb,Mo)ss复合材料的抗氧化性随ZrB2含量的增加而提高,随氧化温度的提高而降低。800℃-1000℃的氧化产物中含有膜状Nb2Zr6O17相,能作为屏障阻止氧气向基体扩散,因此在800℃-1000℃时,复合材料氧化速率较低。然而,在1200℃氧化时未发现Nb2Zr6O17相,MoO3的剧烈挥发和ZrO2的体积效应破坏了Nb2Zr6O17保护层,导致了氧化层严重剥落,材料的抗氧化性极差。综上,本文结合观察到的氧化产物形貌,详细阐述了不同ZrB2含量的复合材料在不同温度下的抗氧化机制。     

Effect of C/SiC Volume Ratios on Mechanical and Oxidation Behaviors of Cf/C-SiC Composites Fabricated by Chemical Vapor Infiltration Technique

C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide (C_f/C-SiC) composites may influence greatly mechanical and oxidation properties of the composites, but have not been well investigated yet. Herein, C_f/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration (CVI) technique through alternating the thickness of a pyrocarbon (PyC) interlayer. The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties. The CS0.37 showed the highest flexural strength of 340.6 MPa, and CS0.84 had the maximum tensile strength of 139.1 MPa. The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities, optimum interfacial bonding and reduced matrix micro-cracks. The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content. The oxidation mechanisms at 1100 °C and 1400 °C were discussed by considering the effect of the C/SiC volume ratios, pores and matrix micro-cracks, oxidation of carbon phase and SiC.