Papers by Keyword: C/C-SiC

Abstract: Liquid Silicon Infiltration (LSI) is a technique to manufacture non-oxide ceramic matrix composites such as C/C-SiC or SiC/SiC. In the beginning of this three-step process, fiber preforms are shaped and impregnated with phenolic resins. After curing, the preforms are pyrolyzed to convert the polymer matrix to a porous carbon matrix. This porosity is then used to infiltrate liquid silicon by capillary forces. Simultaneously, an exothermic reaction of silicon and carbon creates a silicon carbide matrix. Generally the liquid silicon reacts with any carbon and even with SiC present in the form of fibers, fiber coatings or matrix. Therefore, especially the fibers must be protected from Si attack effectively. The morphology of silicon carbide was observed to be heavily driven by Ostwald ripening. This can be suppressed by the addition of boron to the melt. The initially formed SiC crystals in C/C-SiC composites are hereby prevented from grain coarsening, resulting in almost completely preserved C/C blocks. For the manufacture of SiC/SiC composites, the silicon boron alloys allow an effective preservation of the nanocrystalline SiC-fibers. Thus, the use of Si based B containing alloys helps effectively to moderate and control the aggressive reaction during LSI process.

Abstract: C/C-SiC composite as low expansion material for space opto-mechanical structures was prepared by gaseous silicon infiltration after high temperature treatment (HTT) on C/C. 2000°C and 2400°C were selected as the treatment temperatures for C/C to study the influences on the properties of C/C-SiC composite. The graphitization level of amorphous C in C/C was improved by HTT. The porosity of C/C increased from 32.88% to 34.25% (2000°C) and 41.06% (2400°C) respectively. In addition, a higher HTT temperature led to a higher density of C/C-SiC composite and a lower SiC content. Furthermore, the mechanical properties and coefficient of thermal expansion (CTE) of the composite decreased as the temperature increased. After 2000°C HTT, the CTE of C/C-SiC composite decreased to-0.055×10^-6·K^-1 and the mechanical properties (218 MPa) could meet the application demand at the same time.

Abstract: Organic-inorganic hybrid block Poly (silane-b-arylacetylene) (PSbA) have been synthesized through condensation polymerization between chloro-terminated polysilane and diethynylbenzene Grignard reagent, and chloro-terminated polysilane was synthesized through condensation polymerization of dichloromethylvinylsilane in the presence of Mg metal and Lewis acid (ZnCl_2, LiCl). The structures of PSbAs were characterized by FTIR, ¹H, ¹³C, ²⁹Si NMR, and GPC. The PSbAs are orange viscous liquid and can be soluble in common organic solvents at room temperature. The thermal cure behavior of PSbAs was determined by DSC, and the thermal and oxidative stability of the cured PSbAs were investigated using TGA. The results showed that the cured PSbAs exhibit high thermal and thermooxidative stability. The degradation temperatures at 5% weight loss for the cured PSbAs are 470-533°C under N₂ and 378-456°C under air, and the residue yields at 1000°C are 77.9-82.8% under N₂ and 40.4-50.5% under air.

Abstract: C/C-SiC brake composites, based on reinforcement of carbon fiber and dual matrix of carbon and silicon carbide, were fabricated by warm compacted-in situ reacted process. Rules about the influence of different components on the friction and wear characteristics of the C/C-SiC composites are ascertained. As hard particle, the SiC has the function to the formation of friction film, which is in favor of increasing the coefficient of friction (COF) and decreasing the wear rate. The resin carbon plays the role of enhancing the COF, but they are easy to be cut and increase the wear rate. The graphite plays the lubrication function, and right volume content of graphite is helpful to forming friction film to reduce the wear rate. The C/C-SiC composite fabricated by the warm compacted-in situ reaction can with best tribological performance when the components volume fraction of carbon fibre, SiC, graphite and resin carbon are 15.5%, 37.0%, 22.1% and 20.8%, respectively, which the COF and the wear rate can reach the maximum and the minimun value of 0.44 and 1.1μm/cycle respectively.

Abstract: Three-dimensional needle carbon fibre reinforced carbon and silicon carbide dual matrix composite (C/C-SiC) was a new type of high performance brake materials, and exhibited a series of outstanding advantages such as low density, good echanical properties, especially excellent toughness, to avoid catastrophic brittle fracture. In the present study, the C/C-SiC composites were fabricated by the combination of chemical vapor infiltration with liquid silicon infiltration. The preform was prepared by three dimension needling method. The preform was densified by chemical vapor infiltration to form porous carbon/carbon (C/C) composites. Then, the porous C/C composites were converted into C/C-SiC during LSI, in which silicon carbide matrix was formed by the reaction of carbon and melt silicon. The microstructure and mechanical properties of C/C-SiC has been investigated. The results indicated that the composites were composed of 55 wt%C, 39 wt%SiC and 6 wt%Si. The density of C/C-SiC was 2.2 g•cm^-3 and the open porosity was 6.4%, respectively. The C/C-SiC exhibited good echanical properties, especially excellent toughness, to avoid catastrophic brittle fracture. The flexural and compressive strength can reach to 214.6 MPa and 271.0 MPa, respectively. C/C-SiC had excellent impact damage tolerance of 25.2 kJ•m^-2.

Abstract: Continuous carbon fiber reinforced silicon carbide composite material (C/SiC) is one of the most effective candidate materials for hot structures in aeronautic and aerospace applications. Its performances in the complicated service environments are widely concerned. A database, aiming at optimized design of C/SiC, was developed. The database collected original data on the fabrication, microstructure of C/SiC, as well as abundant data on performance experiments including tension, compression, shear, fatigue, creep, oxidation, high-temperature fatigue, and so on. The logic structure of the database, modeled by unified modeling language, provides a data link that connecting the processing, microstructure and performance of C/SiC, so that users can conveniently create a test result set to build the mathematical model of material design. Efficient software was developed to realize management, browsing and extension of the database.

Abstract: The research on ceramic matrix composites and their applications in aerospace field were discussed in terms of their advantages and features, fabrication methods, domestic and foreign research progress, difficulties and key technologies to be solved, and future development trends and directions.

Abstract: The 3D needled C/SiC composites were fabricated by chemical vapor infiltration combined with liquid melt infiltration. The microstructure and compressive behavior of 3D needled C/SiC composites were investigated. The results indicated that the 3D needled C/SiC composites were composed of the layers of 0 ° non-woven fiber cloth, short fiber web, 90 ° non-woven fiber cloth, and needle fibers. The materials were composed of carbon fiber, PyC, Si, and SiC. SiC and Si were mostly distributed in the short fiber web layers. Local C/C units (local carbon fiber reinforced PyC) were formed in the fiber bundles of non-woven fiber cloth. A great deal of pores and cracks existed in the 3D needled C/SiC composites. The pores less than 10 μm were generally located in the non-woven cloth layers, while the big pores were in the short fiber web layers. The cracks were regularly presented in the Si and SiC region of the composites and were normal to the axial direction of the fiber bundles. The compressive strengths perpendicular and parallel to the non-woven fiber cloth were about 118±18 MPa and 260±41 MPa, respectively. The compressive fractography revealed stepwise fracture along fiber layers direction.

Abstract: Acoustic emission (AE) technique was utilized for real-time monitoring the damage evolutions of 2-D and 3-D C/SiC ceramic matrix composites (CMC) under mechanical loading. AE signals for damage initiation and propagation were captured by AE equipment during the entire loading process. Different damage mechanisms of the two kinds of C/SiC composites were revealed on the basis of multi-parameter analysis. The experimental results validate the availability of AE technique on damage monitoring of C/SiC composites. And the AE technique can be used to distinguish the slight differences in damage mechanisms during damage evolution owing to different woven structures.

Abstract: Carbon fibre reinforced carbon and silicon carbide dual matrix composites (C/C-SiC) were fabricated by warm compacted in-situ reaction. The C/C-SiC composites microstructure and tribological properties at different brake speeds were investigated. The results indicated that the composites were composed of 58 wt% C, 37 wt% SiC and 5 wt% Si. The density and open porosity were 2.0 g•cm-3 and 10%, respectively. The C/C-SiC brake composites show excellent tribological performance, including a good stability of brake, the coefficient of friction between 0.57 and 0.67, and the wear rate less than 2.02 cm3•MJ-1. These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems.