Papers by Keyword: SiC Fiber

Abstract: This paper uses a sequential micromechanical method to characterize the thermomechanical properties of a hybrid nanocomposite. It does this by using analytical models (such as the modified rule of mixtures, Tsai-Pagano model, and Schapery model) and numerical models (such as the Finite element model), which are modeled using the commercial software ABAQUS. Investigations are made to determine how the aspect ratio, waviness, and volume fractions of the reinforcement affect the thermo-mechanical performance of the hybrid nanocomposite. It has been shown that adding CNT ESFs to conventional SiC-reinforced titanium alloy composites (TMCs) improves the resulting HTMNC thermo-mechanical properties. It is found that the addition of CNT ESFs to TMCs improves the thermo-mechanical characteristics of the resulting hybrid nanocomposite (i.e., HTMNCs) more in the transverse direction than in the axial direction for all volume fractions of SiC fiber. For instance, it is observed that adding a 2.69% volume fraction of CNT ESFs to the TMCs with a 30% volume fraction of SiC fiber enhances the axial elastic modulus by 2.6% and 2.4% while increasing the transverse elastic modulus by 4.2% and 3.5%, based on the CNT ESFs are straight and wavy. On the other hand, for the same volume fraction of SiC fiber and the addition of 2.69% volume fraction of Straight CNT ESFs, the transverse and axial CTE of the HTMNCs are reduced by 5.33% and 2.53%, respectively. Moreover, when the SiC fiber aspect ratio increases, the axial elastic modulus increases while the transverse elastic modulus exhibits no change. In contrast to the elastic modulus, the CTE increases in the transverse direction while decreasing in the axial direction.

Abstract: Although metal matrix composites (MMC) for the high temperature structural material have been investigated extensively for many years, applications of MMC have been still limited. Among many combinations between the ceramic fibers and the matrix materials, combination of SiC fiber and TiAl based intermetallic compounds has been expected to be one of the best combination, since both SiC fiber and TiAl have demonstrated the capabilities of the low density heat resistant materials. SiC fiber reinforced TiAl composites have been successfully fabricated using hot press method. Optimum temperature and pressure have been determined. SiC/TiAl composite having relatively low fiber volume fraction shows nearly an ideal elastic property applying the law of mixture. Effects of interface layers on the mechanical properties of composites have been studied in detail. Micro-indentation on a single fiber was carried out to examine the pull out strength of SiC fiber quantitatively. Estimated shear stress on the interface was 145-195MPa, those values are quite reasonable since the tensile strength of TiAl matrix was 420MPa and the maximum shear stress would be the half of tensile strength according to Schmid law. Three-point bending tests have been carried out to evaluate the mechanical properties of composites. Fiber volume fraction 8.9% specimen shows ideal bending stiffness compare with the calculated values based on the low of mixture. Reaction layers and the interface between SiC fiber and TiAl have been analyzed by SEM-EDS and XRD. At least two or more reaction layers have been identified. These reaction layers can be explained based on the Si-Ti-C ternary equilibrium phase diagram at 1373K. Optimum conditions of interface structure will be discussed

Abstract: The properties and structure changes of SiC fiber in high temperature determine the service temperature of the reinforced ceramic matrix composites, so the properties of SiC fibers under high temperature are very important. The SiC-A and SiC-B fibers were treated at 1200, 1350 and 1600°C in Ar atmosphere. Then the tensile strength was measured, the microstructure and composition of the fibers were analyzed by SEM, EDS, XRD and AES. The results show that the tensile strength of SiC-A and SiC-B decrease slowly at 1200 and 1350°C, but decrease rapidly at 1600°C.

Abstract: The quasi-static and dynamic compressive mechanical behaviors of two kinds of fiber reinforced SiC ceramic matrix composites including 2D-C/SiC and 2D-SiC/SiC were investigated. Their compressive behaviors of materials at room temperature and strain rate from 10^-4 to 10⁴ /s were studied. The fracture surfaces and damage morphology were observed by scanning electron microscopy (SEM). The results showed that the dynamic failure strengths of 2D-C/SiC and 2D-SiC/SiC obeyed the Weibull distribution. The Weibull modulus of the two materials were 13.70 (2D-C/SiC) and 5.66 (2D-SiC/SiC), respectively. It was found that the two kinds of fiber reinforced ceramic matrix composites presented a transition from brittle to tough with the decrease of strain rate. The 2D-SiC/SiC materials demonstrated a more significant strain rate sensitivity and smoother fracture surface compared to the 2D-C/SiC composites, implying that the former composites present brittle features. This was because the SiC/SiC composites possessed high density and the bonding strength in interface of fiber/matrix is very strong.

Abstract: In order to obtain the near net shaped SiC/SiC composite pins without the processing cost, four kinds of SiC fiber pin preforms including the knitting yarn and core yarn with two dimension braided structure were designed. The SiC/SiC composite pins were fabricated by precursor infiltration pyrolysis (PIP) process used a liquid SiC ceramic precursor. The results showed that, the near net shaped SiC/SiC composite pins could be obtained by using the designed SiC fiber preform and the graphite mould with curved groove. The macrostructure and microstructure of the SiC/SiC composite pins were observed by scanning electron microscope. Both the single shear stress-displacement curves and the double shear stress-displacement curves of the different kinds of SiC/SiC composite pins showed the saddle-shaped, which indicated the fracture model of the SiC/SiC composites pins was non-catastrophic, and the SiC/SiC composite pins in this paper possessed the secondary bearing capacity. This paper may provide some new ideas for fiber reinforced SiC ceramic matrix composites components designers.

Abstract: To prevent the strong interfacial reactions in SiC fiber reinforced nickel-based superalloys matrix composites, yttrium oxide (Y₂O₃) was used as the barrier coating by reaction magnetron sputtering method. Compared with the composites without coating, after the high temperature hot isostatic pressing (HIP), Y₂O₃ coating effectively protected the SiC fibers from the interfacial reactions, and no element diffusion can be observed between the fibers and the matrix. The elevated temperature tensile tests were performed on both SiC/GH4738 and SiC/Y₂O₃/GH4738 composite. The results indicated that the strength of the composites with Y₂O₃ coating can increase about 35% in comparison with the composites without coating.

Abstract: As for gasoline vehicles, the particulate matter (PM) emissions from traditional port fuel injection (PFI) engines are pretty low. Recently, the gasoline direct injection (GDI) vehicles have been gaining market share globally due to better fuel efficiency, especially in the European countries. A drawback associated with GDI engines is considerably higher PM emissions compared with PFI engines. The soot in gasoline exhaust gas would contribute to urban air pollution, which is deeply related with adverse health effects. For the reduction of PM emission in Europe, a new regulation known as EURO VI has been set recently. Then, we need to trap soot particles in exhaust gas from gasoline automobiles as well as diesel automobiles. However, the gasoline soot would be much smaller than the diesel soot. Also, the gasoline exhaust gas temperature is much higher. Then, we need gasoline particulate filter (GPF) which needs to have better thermal durability. In this study, as a potential GPF, an SiC fiber filter was numerically examined. The effect of the fiber diameter on the filtration was revealed. Results show that, when the filter of the larger fiber diameter is placed more upstream, the deposition of soot particles widely occurs inside the filter, resulting in the lower pressure drop.

Abstract: In this work, the influences of composition and microstructure on the mechanical properties and thermal stability of SiC ceramic fibers were investigated. XPS, XRD, SEM, and element analysis were used to analyze the elemental composition and structural morphology. The contents of oxygen and free carbon influence the crystallinity of SiC fibers, which inhibit the grain growth of β-SiC. The reduction of tensile strength of the fibers sintered under temperatures above 1700°C is attributed to the appearance of massive defects on the outer surface of the fibers, which can be overcome by the change of sintering conditions of the pyrolysis fibers.

Abstract: Two different polycarbosilane (PCS) fibers were prepared by a new oxygen-free curing method and Chemical Vapor Curing (CVC), respectively. Nearly stoichiometric SiC fiber was prepared via hydrogenation in H₂-N₂ mixture and subsequent sintering in inert gases. The green PCS fiber and nearly stoichiometric SiC fiber were characterized by FT-IR, XRD, SEM etc. Meanwhile, the effect of hydrogenation on the thermal stability of SiC fibres cured by CVC method was studied. It was found that the oxygen-free curing method can effectively decrease the content of oxygen in the final SiC fiber, while the hydrogenation treatment can dramatically diminish the content of free carbon, so the nearly stoichiometric SiC fiber with C/Si atomic ratio being 1.06 can be obtained. After the heat-treated at 1600°C in inert gases, the strength retaining ratio of the oxygen-free cured SiC achieved 68%, demonstrating that the nearly stoichiometric SiC fiber possesses excellent high-temperature stability and higher anti-oxidation property.

Abstract: Up to now, many types of inorganic fibers have been developed. The main purpose is to develop composite materials with lightweight and high fracture toughness. Of these, carbon fiber has already established a very big market. By the way, representative oxide fibers (alumina/silica-based fibers) show heat-resistance’s limitation at around 1200°C. In order to improve the heat-resistance, some types of eutectic oxide-fibers have been studied. On the other hand, SiC fibers with both heat-resistance and oxidation-resistance were developed over 30 years ago. After that, lots of improvements have been performed, and finally several types of excellent heat-resistant SiC-polycrystalline fibers, which can be used up to about 1800°C, were developed from polycarbosilane. Using these fibers, lots of applications have been considered in the fields of aerospace, nuclear system, and so on. Furthermore, making the best use of the aforementioned production process, several types of functional ceramic fibers with gradient-like functional surface layers also have been developed. In this paper, of these inorganic fibers, heat-resistant SiC fibers will be addressed along with historical view point on ceramic fibers.