化学气相渗透法制备三维针刺C/SiC复合材料的烧蚀性能

用化学气相渗透法制备了三维针刺碳纤维增强碳化硅陶瓷基复合材料,复合材料的平均密度为2.15 g/cm3,气孔率为16.0%.用氧乙炔焰研究了复合材料的烧蚀性能,用扫描电镜分析了烧蚀表面的形貌,用表面能谱分析了烧蚀产物的成分.复合材料的线烧蚀率和质量烧蚀率分别为0.03mm/s和0.004 7 g/s.在烧蚀中心区,烧蚀最严重,表层只有C纤维骨架,且C纤维呈针状,复合材料的烧蚀以升华和冲刷为主.在烧蚀过渡区,垂直于烧蚀面的C纤维表现出端部锐化、根部细化的特性,平行于烧蚀面的C纤维呈针状,复合材料的烧蚀以氧化和机械剥蚀为主.烧蚀边缘烧蚀不明显,烧蚀产物和SiC基体熔融后覆盖在烧蚀表面,阻碍了复合材料的进一步烧蚀,复合材料的烧蚀以氧化为主.     

CVI法快速制备C/SiC复合材料

为缩短CVI法制备C／SiC复合材料的工艺周期并降低成本，研究了CVI工艺过程中沉积温度、MTS（CH3SiC3)摩尔分数和气体流量对SiC沉积速率和MTS有效利用率的影响，实验结果表明：提高沉积温度，常压下1100℃时增大MTS摩尔分数（11％→19％），都有利于提高SiC沉积速率；提高沉积温度和降低反应物气体流量，能提高MTS有效利用率，在优化的工艺条件下，预制体的微观孔隙内沉积了致密的SiC基体，沉积速率达到142μm/h左右，并有效消除了基体中裂纹的形成，MTS的有效利用率为11％－27％。     

先驱体浸渗裂解法制备C/C-SiC复合材料的烧蚀性能

用先驱体浸渗裂解法制备了碳纤维增强碳(carbon fiber reinforced carbon,C/C)-SiC复合材料,用H2-D2火焰法检测其烧蚀性能.结果表明:C/C-SiC复合材料的烧蚀率随复合材料中的Si含量的增加而呈下降趋势;经过5次浸渍,C/C-SiC复合材料的密度从1.46 g/cm3增加到1.75 g/cm3,Si含量从5.06%增加到13.8%,线烧蚀率和质量烧蚀率分别下降474%和34.5%.密度为1.75g/cm3的C/C-SiC复合材料,其线烧蚀率和质量烧蚀率分别为2.22 μm/s和1.289 mg/s,其线烧蚀率和质量烧蚀率分别为密度1.78 g/cm3的C/C复合材料的21.7%和78.6%.基体中SiC的引入明显提高了C/C复合材料的抗氧化烧蚀性能.     

PyC/SiC界面改性C/C-SiC-ZrC复合材料的等离子烧蚀性能研究

以丙烯(C3H6),三氯甲基硅烷(MTS)为原料,利用化学气相渗透(CVI)技术在炭纤维预制体的纤维表面依次制备了热解炭(PyC)与碳化硅(SiC)界面层,随后结合CVI及前驱体浸渍裂解(PIP)工艺对材料进行增密,制得了密度为1.92 g/cm3的界面改性C/C-SiC-ZrC复合材料.利用X射线衍射仪(XRD)与扫...     

化学气相渗透2.5维C/SiC复合材料的拉伸性能

采用等温减压化学气相浸渗(isothermal low-pressure chemical vapor infiltration,ILCVI)工艺制备了在厚度方向上具有纤维增强的2.5维(2.5 dimensional,2.5D)碳纤维增强碳化硅多层陶瓷基复合材料,从而使一端封口的防热结构部件的制备成为可能.ILCVI致密化后,复合材料的密度、孔隙率分别为1.95～2.1 g/cm3和16.5%～18%.沿经纱和纬纱两个方向对2.5D C/SiC复合材料进行室温拉伸实验.结果表明:复合材料在纵向和横向的拉伸应力-应变均表现为明显的非线性行为.复合材料具有较高的面内拉伸性能,纵横向的拉伸强度分别为326MPa和145MPa,断裂应变分别为0.697%和0.705%.复合材料的拉伸断裂为典型的韧性断裂,经纱和纬纱的断裂都表现为纤维的多级台阶式断裂以及纤维的大量拔出.     

炭基体结构状态对C/C复合材料抗烧蚀性能的影响

碳基体在C／C复合材料的组成中占有很大的比重，因此炭基体不同的结构状态往往对C／C复合材料的各项性能有显著的影响。本文利用不同的原料和加工工艺制备出了三种具有不同炭基体的C／C复合材料，这三种碳基体分别是热解炭，沥青炭以及解热炭－树脂炭混合炭基体。对这三种材料多项性能的测试结果表明，炭基体的结构状态如石墨化度，炭片层结构的取向度的不同对C／C复合材料的各项性能均有显著的影响；基本趋势是C／C材料的石墨化度越高，材料的导电性能，导热性能以及抗烧蚀性能越好，压缩强度越低。三种炭基体中沥青炭基体沿纤维轴向的取向度最低，其抗烧蚀性能最差。     

C／SiC复合材料热性能及抗氧化性能的研究

本文研究了聚碳硅烷化学转化法制备C/SiC复合材料过程中碳纤维(CF)、碳化硅(SiC)基体的热物理性能对C/SiC复合材料性能的影响,并提出了一种可以提高复合材料抗氧化能力的简单有效的方法。     

环氧树脂/改性SiC复合材料的制备及性能

采用硅烷偶联剂KH-560和丙烯酰胺对SiC进行表面改性,将其添加到环氧树脂中制备环氧树脂/改性SiC复合材料.采用傅里叶变换红外光谱仪、X射线衍射仪以及接触角测试仪探究改性SiC的性能,并对复合材料的性能进行测试.结果表明:SiC表面带有憎水基团,与环氧树脂相容性提高;SiC用量为环氧树脂质量的20％时,拉伸强度和弯...     

Microstructure and Mechanical Properties of Three-Dimensional Textile Hi-Nicalon SiC/SiC Composites by Chemical Vapor Infiltration

Three-dimensional textile Hi-Nicalon SiC-fiber-reinforced SiC composites were fabricated using chemical vapor infiltration. The microstructure and mechanical properties of the composite materials were investigated under bending, shear, and impact loading. The density of the composites was 2.5 g·cm⁻³ after the three-dimensional SiC perform was infiltrated for 30 h. The values of flexural strength were 860 MPa at room temperature and 1010 MPa at 1300°C under vacuum. Above the infiltration temperature, the failure behavior of the composites became brittle because of the strong interfacial bonding and the mismatch of thermal expansion coefficients between fiber and matrix. The fracture toughness was 30.2 MPa·m^1/2. The obtained value of shear strength was 67.5 MPa. The composites exhibited excellent impact resistance, and the dynamic fracture toughness of 36.0 kJ·m⁻² was measured using Charpy impact tests.     

无压烧结碳化硅复合材料的制备与性能研究

以部分碳化钛为增强相投入到碳化硅基体材料中,并投入微量炭黑和碳化硼为烧结活化剂,利用无压固相烧结技术制造了碳化硅基陶瓷复合材料。评测了其力学性能,凭借扫描电镜(SEM)观测了试样的断口形貌与表观形貌,并探讨了其氧化行为。结果表明:在碳化硅中投加部分碳化钛,对复合材料的力学性能有非常大地益处,于9 wt%时达到顶峰,弯曲强度497 MPa,相对密度98.9%,断裂韧性4.79 MPa·m^1/2。复合材料的显微组织构造紧致密实,TiC颗粒在SiC材料中的离散作用而激发的钉扎效果和裂纹偏移转向为其主要的增韧原理。在设定的氧化条件下(1200℃保温2 h),试样表面形成了一层较为致密并可以弱化氧化进程的氧化膜层。     

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。     

Preparation of SiC/SiC Composites by Hot Pressing, Using Tyranno-SA Fiber as Reinforcement

The development of advanced Tyranno SA SiC fiber with a near-stoichiometric composition and a well-crystallized microstructure has made it possible to prepare SiC/SiC composites even under harsh conditions. To assess the reinforcing effectiveness of Tyranno SA fiber at high temperature under pressure, unidirectional SiC/SiC composites were prepared by hot pressing, using pyrolytic carbon (PyC)-coated Tyranno SA fiber as a reinforcement and nanopowder SiC with sintering additives for matrix formation. The effects of sintering conditions on the microstructural evolution and mechanical properties of the composites were characterized. As the sintering temperature increased (from 1720° to 1780°C) and the sintering pressure increased (from 15 to 20 MPa), the density of the composites gradually increased. Simultaneously, the elastic modulus, the proportional limit stress, and the strength, under both bend and tensile tests, also improved. At lower temperature and/or pressure, long fiber pullout was a predominant fracture behavior, indicating relatively weak fiber/matrix bonding. However, at high temperature and/or pressure, short fiber pullout became a main fracture characteristic, indicating relatively strong fiber/matrix bonding. These phenomena were also confirmed by the characteristics of the hysteresis loops derived from the stress–strain curves produced by a tensile test with unloading–reloading cycles. In the present investigation, the reinforcement of Tyranno SA fiber is effective for providing noncatastrophic fracture behavior to composites.     

反应熔渗法制备C/C-SiC复合材料及其反应机理和动力学的研究进展

对反应熔渗法制备C/C-SiC复合材料过程中Si的渗入行为以及Si/C的反应机理和动力学进行了综合评述.分析了高温下Si的密度、粘度、表面张力及Si/C润湿角对渗入能力的影响.概括了Washburn公式及其改进模型在液Si渗入行为方面的研究进展,给出了渗入时间、SiC生成速率与渗入高度之间的关系.对控制Si/C反应的溶解-沉淀机理和扩散机理进行了阐述,总结分析得出：不同阶段Si/C反应发生的区域不同,因而控制反应的机理也不同.最终的SiC相是由不同反应机理共同作用形成的.     

A Process for Cf/SiC Composites Using Liquid Polymer Infiltration

A continuous carbon fiber/silicon carbide matrix composite material has been produced by a low-cost process. In this process the space in a two-dimensional carbon fiber preform is filled with a SiC powder by a pressure infiltration method. High particle packing densities are achieved within the fiber preform in this way. The compact body is heat-treated at 400°C to form a porous framework, which is then infiltrated with a liquid preceramic polymer, Ceraset^TM SN. Subsequently the infiltrated polymer is pyrolyzed in argon at 1300°C. The microstructure of the final composite is characterized, and mechanical properties of these composites are discussed.     

Preparation of C/C‐SiC Composites from All‐Cellulose Precursors

All‐cellulose composites (ACCs) are manufactured from high‐performance cellulose fibers and a cellulose‐containing ionic liquid (IL) as matrix‐forming dope via wet‐winding processes, using different concentrations of cellulose in the IL. ACCs are carbonized at 1650 °C and then infiltrated with liquid silicon. Application of a carbonization aid (ammonium dihydrogenphosphate, ADHP) substantially improves the carbon yield after carbonization but also results in the depletion of the mechanical properties of the final carbon/carbon silicon carbide (C/C‐SiC) material. The microstructure of the porous carbon/carbon preforms strongly depends on both the concentration of cellulose in the IL and the concentration of ADHP. A C/C‐SiC composite manufactured from 6 wt% cellulose in the matrix‐forming dope, in the absence of ADHP, has a maximum flexural strength of 60 MPa. New C/C‐SiC composites with different shapes including Z‐profiles and tubes are successfully manufactured from pre‐shaped ACC precursors. These composites keep their shape during carbonization and the final siliconization process step.     

Reactive Hot Pressing of ZrB2–SiC Composites

A ZrB₂–SiC composite was prepared from a mixture of zirconium, silicon, and B₄C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa·m^1/2. The microstructure of the composite was observed via scanning electron microscopy; the in-situ -formed ZrB₂ and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B₄C will diffuse into the Zr and Si sites and form ZrB₂ and SiC in situ , respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.