SiC收尘粉和石油焦凝胶注模成型制备反应烧结SiC陶瓷

采用SiC收尘粉和石油焦为原料,粉体经提纯和表面改性后,凝胶注模成型(Gelcasting,GC)制备坯体,在真空炉中1600℃液相渗硅2h制备反应烧结SiC( Reaction bonded silicon carbide,RBSC)陶瓷.Zeta电位值和流变曲线显示,酸洗和粉体改性有效改善了SiC粉的分散性能.浆料粘度随石油焦添加量的增加上升.添加16～18wt％的石油焦,浆料的浓度为50vol％时,粘度介于600～900 mPa·s,满足凝胶注模成型的要求.素坯碳密度(c)可控制在0.81～0.84g/cm3之间,RBSC的密度和三点抗弯强度分别为3.07～3.10g/cm3和425～653MPa,而且材料的显微结构均匀.实现了以SiC收尘粉和石油焦为原料GC成型制备离性能RBSC材料的目标.     

SiC纳米线增强反应烧结碳化硅陶瓷的性能研究

以单晶SiC纳米线作为增强体,碳化硅-碳为陶瓷基体,在1550℃下,采用反应烧结制备碳化硅基陶瓷复合材料(SiCnf/SiC).结合X射线衍射、万能试验机和扫描电镜等检测和分析,研究SiC纳米线对复合材料的微结构和力学性能的影响.研究表明:与未加入SiC纳米线的反应烧结碳化硅陶瓷相比,添加SiC纳米线的复合陶瓷的抗弯强度和断裂韧性都得到显著的提高,抗弯强度提高了52％,达到320 MPa(SiC纳米线含量为12wt％),断裂韧性提高了40.6％,达到4.5 MPa· m1/2(SiC纳米线含量为15wt％);反应后的SiC纳米线仍然可以保持原有的竹节状结构,且随着SiC纳米线的加入,复合陶瓷的断口可以观察到SiC纳米线拔出现象.但由于SiC纳米线“架桥”的现象,添加过量的纳米线会降低复合陶瓷的密度和限制复合陶瓷力学性能的提高.同时还讨论了SiCnf/SiC的增强机理.     

反应浸渗法制备SiC/FeSix复合材料

研究了在SiC+C坯体中加入Fe粉,用熔融Si进行反应浸渗,以制备不合游离Si的SiC/FeSix复合材料.结果表明:用本实验方法通过调整坯体中Fe含量可以制得不合游离Si的SiC/FeSix复合材料,该材料在室温下的抗弯强度为(220±10)MPa.文中推导了Fe含量与第2相组成的理论模型,同时讨论了热处理工艺对烧结的影响.     

裂解碳包覆对SiC纳米纤维增强SiC陶瓷基复合材料性能的影响

以SiC纳米纤维(SiC_nf)为增强体,通过化学气相沉积在SiC纳米纤维表面沉积裂解碳(PyC)包覆层,并与SiC粉体、Al₂O₃-Y₂O₃烧结助剂共混制备陶瓷素坯,采用热压烧结工艺制备质量分数为10%的SiC纳米纤维增强SiC陶瓷基(SiC_nf/SiC)复合材料。研究了PyC包覆层沉积时间对SiC_nf/SiC陶瓷基复合材料的致密度、断裂面微观形貌和力学性能的影响。结果表明:在1 100 ℃下沉积60 min制备的PyC包覆层厚度为10 nm,且为结晶度较好的层状石墨结构;相比于纤维表面无包覆层的复合材料,复合材料的断裂韧性提高了35%,达到最大值(19.35±1.17) MPa·m^1/2,抗弯强度为(375.5±8.5) MPa,致密度为96.68%。复合材料的断裂截面可见部分纳米纤维拔出现象,但SiC_nf/SiC陶瓷基复合材料界面结合仍较强,纳米纤维拔出短,表现为脆性断裂。     

SiC组分含量对SiC/Cu复合材料力学性能的影响

采用真空热压法制备了不同配比的SiC/Cu金属陶瓷复合材料.利用阿基米德原理测定了复合材料的密度及气孔率;利用Instron万能材料电子试验机测得其三点弯曲强度;采用Hv-1000显微硬度仪测试其显微硬度,采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对烧成样品的物相组成和断口显微形貌进行表征.结果表明:随着SiC组分含量的增加,SiC/Cu复合材料的致密度、抗弯强度均有所下降,而气孔率和显微硬度显著增加.在750 ℃,30 MPa压力作用下,保温3 min,制备得到的30SiC/70Cu(vol%)的复合材料,具有最优的力学性能,其显微硬度达到2087.2 MPa,抗弯强度为174.0 MPa.SiC/Cu复合材料的断裂行为既表现出一定的微观韧性特征,又表现出一定的脆性特征.     

纳米SiO2对先驱体浸渍裂解法制备SiCf/SiC复合材料力学性能的影响

以纳米SiO2为填料,采用先驱体浸渍裂解法制备2.5D-SiCf/SiC（D为维数,SiCf为SiC纤维）复合材料,研究了前驱液中纳米SiO2含量对复合材料力学性能的影响。结果表明,纳米SiO2的添加能有效抑制先驱体裂解过程中的体积收缩,提高致密度,但过量引入易导致浸渍液黏度过高,浸渍效率降低。纳米SiO2含量对材料力学性能有较大影响,添加纳米SiO2后材料的抗弯强度和断裂韧性均高于没有添加的样品,材料抗弯强度随纳米SiO2含量的增加先增大后降低。当浸渍液中纳米SiO2含量为6%时,复合材料具有优异的力学性能,抗弯强度达到211.1MPa。     

SiC/(W,Ti)C陶瓷喷嘴材料的制备及其性能

本文以SiC为基体,添加(W,Ti)C固溶体增韧相,采用热压烧结工艺制备出新型Sic/(w,Ti)C陶瓷复合材料.研究表明:SiC/(W,Ti)C陶瓷材料的性能与(W,Ti)C的含量、成烧温度、保温时间等密切相关.随(W,Ti)C含量的增加,材料的致密度、抗弯强度和断裂韧性增加,硬度减小;SiC/(W,Ti)C陶瓷复合材料的最佳性能参数为:抗弯强度631 MPa,维氏硬度25.944 GPa,断裂韧性4.38 MPa·m1/2.通过分析材料的显微结构和断口SEM照片,发现SiC/(W,Ti)C陶瓷材料的断裂机制为沿晶和穿晶断裂特征同时并存,即断裂方式为沿晶断裂和穿晶断裂相结合的混合断裂.     

低温制备SiC多孔陶瓷及性能

采用SiC微粉为骨料,聚碳硅烷为粘结剂,混合后溶于THF中干燥过筛,经模压成型后于1000℃保护气氛下低温烧结制备SiC多孔陶瓷。运用XRD、SEM及孔隙率测定手段对陶瓷样品的物相结构、微观形貌及孔隙率进行研究,考察了不同聚碳硅烷含量对SiC多孔陶瓷抗弯强度、线收缩率及气孔率的影响。结果表明,随着聚碳硅烷含量的增加,SiC多孔陶瓷的线收缩率和失重比均增加,抗弯强度和显气孔率均先增加后下降,抗弯强度在聚碳硅烷含量为13%时达到最大值为58.45MPa,开口气孔率在PCS含量为5%时达到最大值为37.2%。     

浆料中SiC粉含量对PIP法Cf/Si-O-C复合材料结构与性能的影响

以三维碳纤维编织物和硅树脂(SR249)为原料,采用先驱体转化法(PIP)制备了Cf/Si-O-C复合材料,考察了浆料中SiC粉含量对Cf/Si-O-C的结构与性能的影响.结果表明:由于浆料中SiC粉含量的不同,复合材料的性能与结构具有明显差异.随着浆料中SiC粉含量的增加,Cf/Si-O-C材料的气孔率降低,纤维/基体界面结合减弱,导致其力学性能有明显提高.     

Nicalon SiC纤维增强SiC复合材料制备工艺研究

本文对SiC纤维增强SiC复合材料的制备工艺进行了研究.将Nicalon SiC短纤维、SiC颗粒、钾长石、高岭土按设计的配方通过干法混合,干压成型后采用常压烧结法制备出SiCf/SiC复合材料;利用DTA分析混合粉体的热物理性能,采用XRD分析烧成前后材料的物相,利用SEM观察样品的显微结构,并测定了样品的致密度和抗弯强度.研究结果表明:常压烧结温度1115 ℃,保温时间2 h可制备出性能良好的SiCf/SiC复合材料.     

基于核应用下碳化硅陶瓷及其复合材料的连接研究进展

SiC陶瓷及其复合材料凭借其自身固有的核辐射下的稳定性而有望成为新一代核裂变以及未来核聚变反应堆中重要的结构材料.能否满足核应用环境下各种苛刻条件而实现完美连接是其能够得到最终应用的关键.本文综述了目前国际上基于核应用上SiC陶瓷及其复合材料的几种连接工艺的发展情况.     

SiC/SiC复合材料及其应用

日本开发的Nicalon和Tyranno两种品牌的SiC纤维占有世界上绝对性的市场份额。SiC/SiC复合材料典型的界面层是500 nm厚的单层热解碳(PyC)涂层或多层(PyC-SiC)n涂层,在湿度燃烧环境及中高温条件下界面层的稳定性是应用研究的重点。SiC/SiC复合材料,包括CVI-SiC基体和日本开发的Tyranno hex和NITE-SiC基体等,具有耐高温、耐氧化性和耐辐射性的特点,在航空涡轮发动机部件、航天热结构部件及核聚变反应堆炉第一壁材料等方面正开展工程研制应用。     

Pressure‐less joining of C/SiC and SiC/SiC by a MoSi2/Si composite

A MoSi₂/Si composite obtained in situ by reaction of silicon and molybdenum at 1450°C in Ar flow is proposed as pressure‐less joining material for C/SiC and SiC/SiC composites. A new “Mo‐wrap” technique was developed to form the joining material and to control silicon infiltration in porous composites. MoSi₂/Si composite joining material infiltration inside coated and uncoated C/SiC and SiC/SiC composites, as well as its microstructure and interfacial reactions were studied. Preliminary mechanical strength of joints was tested at room temperature and after aging at service temperatures, resulting in interlaminar failure of the composites in most cases.     

Polymer-derived SiC ceramic aerogels with in-situ growth of SiC nanowires

Herein, the SiC ceramic aerogels with in-situ growth of SiC nanowires (SiC_w/SiC CAs) have been synthesized by polymer‐derived ceramics (PDCs) method. The morphology, microstructure, and phase composition of the as-prepared samples were systematically investigated through SEM, XRD, TEM, Raman spectrum, FT-IR spectrum, and XPS spectrum techniques. The results showed that the as-obtained SiC_w has a diameter of about 80 nm and a length of 1–3.5 μm. In addition, the formation mechanism and evolution process of growth SiC_w were systematically studied using a VLS growth mechanisms. The way in this work could be expanded to synthesize other Si-based porous ceramic aerogel nanostructed with nanowires.     

Microstructure and tensile behavior of (BN/SiC)n coated SiC fibers and SiC/SiC minicomposites

Interphase plays an important role in the mechanical behavior of SiC/SiC ceramic-matrix composites (CMCs). In this paper, the microstructure and tensile behavior of multilayered (BN/SiC)_n coated SiC fiber and SiC/SiC minicomposites were investigated. The surface roughness of the original SiC fiber and SiC fiber deposited with multilayered (BN/SiC), (BN/SiC)₂, and (BN/SiC)₄ (BN/SiC)₈ interphase was analyzed through the scanning electronic microscope (SEM) and atomic force microscope (AFM) and X-ray diffraction (XRD) analysis. Monotonic tensile experiments were conducted for original SiC fiber, SiC fiber with different multilayered (BN/SiC)_n interfaces, and SiC/SiC minicomposites. Considering multiple damage mechanisms, e.g., matrix cracking, interface debonding, and fibers failure, a damage-based micromechanical constitutive model was developed to predict the tensile stress-strain response curves. Multiple damage parameters (e.g., matrix cracking stress, saturation matrix crack stress, tensile strength and failure strain, and composite’s tangent modulus) were used to characterize the tensile damage behavior in SiC/SiC minicomposites. Effects of multilayered interphase on the interface shear stress, fiber characteristic strength, tensile damage and fracture behavior, and strength distribution in SiC/SiC minicomposites were analyzed. The deposited multilayered (BN/SiC)_n interphase protected the SiC fiber and increased the interface shear stress, fiber characteristic strength, leading to the higher matrix cracking stress, saturation matrix cracking stress, tensile strength and fracture strain.     

Microstructure and mechanical properties of hot-pressed SiC nanofiber reinforced SiC composites

This study reports on the preparation and mechanical properties of a novel SiC_nf/SiC composite. The single crystal SiC nanofiber(SiC_nf) reinforced SiC ceramic matrix composites (CMC) were successfully fabricated by hot pressing the mixture of β-SiC powders, SiC_nf and Al–B–C powder. The effects of SiC_nf mass fraction as well as the hot-pressing temperature on the microstructure and mechanical properties of SiC_nf/SiC CMC were systematically investigated. The results demonstrated that the 15 wt% SiC_nf/SiC CMC obtained by hot pressing (HP) at 1850 °C with 30 MPa for 60 min possessed the maximum flexural strength and fracture toughness of 678.2 MPa and 8.33 MPa m^1/2, respectively. The nanofibers pull out, nanofibers bridging and cracks deflection were found by scanning electron microscopy, which are believed can strengthen and toughen the SiC_nf/SiC CMC via consuming plenty of the fracture energy. Besides, although the relative density of the prepared SiC_nf/SiC CMC further increased with the sintering temperature rose to 1900 °C, the further coarsend composites grains results in the deterioration of the mechanical properties for the obtained composites compared to 1850 °C.     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

SiC窑具材料氧化动力学方程的研究

在硅微粉结合的SiC窑具材料中添加少量的铁矿渣矿化剂,使窑具在高温下形成一定量的液相,能使体积效应大的α-方石英转化成体积效应小的α-鳞石英,降低窑具的体积效应和提高热稳定性。同时形成的液相能使S i C表面形成一层致密的保护膜,堵塞气孔,隔离O2与SiC的接触,降低在界面上进行的氧化反应速度,以达到抗氧化的目的。实验结果表明:添加0.4%铁矿渣矿化剂的氧化度最小(G=6.1x10-5),确定0.4%为最佳的铁矿渣加入量。在1300℃下铁矿渣添加量分别为0和0.4wt%时的氧化动力学方程分别为:F(G1)=3.17×10-9,F(G2)=1.75×10-9     

锆石/SiC复合物的抗热震性

测试锆石/碳化硅(30%)复合试样的抗热震性需要在高于1 000℃的温度下进行,并与气孔率值几乎相同的纯锆石试样相比较.结果证实了淬火试样的断裂应力未受到合成SiC微粒对淬火温度升高的影响.另一方面,发现重要的温差△T在复合物中要高于纯锆石试样,低于它时材料保持其初始强度.X-射线衍射分析显示了复合试样表面层的锆石分解并生成了由内核和外壳组成的试样.