Papers by Keyword: Ceramic Matrix Composite (CMC)

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.

Abstract: Self healing of surface cracks is the most effective function to ensure the structural integrity for ceramic components, because even minute surface crack give rise to a large strength decrease because of its high sensitivity to flaws. The present author and coworkers succeeded that the degraded strength due to cracking can be completely recovered by self crack healing ability driven by the high temperature oxidation of silicon carbide. Then, the mechanism and the effect of the self-healing were investigated. The most attractive feature of the self healing is to be able to respond to the damage caused during service. Thus, enhancement in self healing velocity has been necessary to actualize the self healing ceramics. In the present study, nanometer sizing the disperse silicon carbide particle was attempted to achieve the purpose. Alumina composites containing various shapes of silicon carbide nanometer sized particles were synthesized from mullite, aluminum and carbon powders. From the strength recovery behaviors of these alumina/ silicon carbide composites, the following aspects were derived. Silicon carbide particles nanometer sizing can heal completely the surface cracks at lower temperature and shorter time.

Abstract: Three non-destructive test (NDT) methods were used to detect the two dimensional C/SiC specimens after low velocity impact (LVI) of various energies. The damage areas characterized by these methods were very different. Both ultrasonic and thermographic images reveal the LVI damages, while X ray is non-sensitive to the interior damage. However, small delaminations were not found by thermography and accurate judgment depends on the experience and the resolution of the infrared camera. And the result acquired from the higher frequency transducer was very confused because of the inherent defects. It is suggested that using both ultrasonic C-scan and thermography to evaluate the LVI damage of C/SiC. It is also suggested using the transducer of low frequency to perform the ultrasonic C-scan.

Abstract: Carbon fiber reinforced silicon carbonitride ceramic composite (C/SiCN) was prepared by rapid electro-thermal pyrolysis chemical vapor deposition using liquid hexamethyldisilazane as precursor. The density of C/SiCN is 1.75g/cm3 and with 15% porosity. Microstructure characteristics of C/SiCN were examined by transmission electron microscopy and scanning electron microscope equipped with energy dispersive spectrometer. The mechanical properties were characterized by three-point bending test. Microstructure observation displays a high degree of coalescence between SiCN matrix and fiber filaments, but there also exist plenty of micro-pores within fiber bundle. It is different from that of C/SiC composite made by chemical vapor infiltration. Mechanical test exhibits a mostly obvious nonlinear fracture behavior, which can be explained by typical toughening mechanism of long fiber-reinforced ceramic matrix composite.

Abstract: C/C-SiC brake materials were prepared by improved chemical liquid vaporized infiltration (CLVI) combined with liquid silicon infiltration (LSI) process, which needed less than thirty hours. The microstructure and frictional properties of the material were investigated. The density and porosity of the C/C-SiC brake material were 2.05 g/cm3 and 4.8%, respectively. The average dynamic friction coefficient of the materials was about 0.36, and the friction coefficient was stable. The average linear wear rate was less than 4.7 µm cycle-1 for rotating and stationary disk. The matrix composition and microstructure resulted in the high frictional performances.

Abstract: In this paper, the influences of different binders (Hydroxypropyl Methyl Cellulose (HPMC), Carboxymethyl Cellulose Sodium (CMC), Polytetrafluoroethylene (PTFE) and Styrene- butadiene Rubber (SBR)) on high-rate discharge performances at low temperature for the negative electrode of Ni/MH battery have been studied by orthogonal experimental design. Electrochemical measurements have been conducted to investigate the capacity, charge-discharge performance, cyclic voltammetry and electrochemical impedance characteristics. The surface morphology and chemical compositions have been investigated by SEM and EDS. Based on the range analysis, the primary and secondary influence factors as well as the optimization results were obtained. From the CV characteristic curves, the oxidization peaks and reduction peaks are not clearly shown, which indicates that the redox reaction does not occur clearly after binders added. The EIS experiments show that the deterioration of the voltage characteristic of the battery is due to drying out of the separator that increases the ohmic resistance (Rs ), and the decay of the discharge capacity is due to the passivity surface that increases the charge-transfer resistance (Rt) of the battery.

Abstract: Carbon nanotubes (CNTs) are promising reinforcing elements for structural composites due to their remarkable mechanical properties. The impressive electrical and thermal properties of this new form of carbon also make CNTs containing composites ideal candidates for multifunctional applications. In the past decade, researchers have investigated CNTs as toughening inclusions to overcome the intrinsic brittleness of ceramics and glasses. Although there are numerous investigations available in the literature, a significant progress has not occurred or it has been rather slow compared to advances in the field of CNT/polymer matrix composites. This paper reviews current trends in research and development efforts on the use of CNTs for fabrication of ceramic and glass matrix composite materials. The review includes a summary of key issues related to the optimisation of CNT-based composites and an overview of investigations dealing with processing techniques developed to optimise dispersion quality, interfaces and density. The mechanical properties of as-produced composites are discussed and a comprehensive comparison of data available for different matrix materials is presented. Finally, the potential applications of the resulting CNT/inorganic matrix composites and the scope for future developments in the field are highlighted.

Abstract: Several 2D SiCf-SiC and Cf-SiC composites were fabricated using isothermal and isobaric Chemical Vapour Infiltration (ICVI) process. The reinforcements used in the above composites are Nicalon CG fabric and C fabric. Prior to SiC matrix infiltration, BN and C interfaces were applied to the fibre by using the pre-cursors Boron Trichloride (BCl3)-Ammonia (NH3) and Methane (CH4) respectively to improve the mechanical performance of the composites. SiC matrix was infiltrated by the decomposition of Methyl Trichloro Silane-CH3SiCl3 (MTS) in the presence of hydrogen at the temperature ranging from 950°C to 980°C. H2/MTS flow rate ratio used for this study is 16:1.An appropriate temperature for uniform SiC infiltration without any premature pore closures have been obtained by kinetic experiment. Density and porosity of the above composites were measured using the method described by EN1389:2003. Various mechanical characterizations like flexural strength, tensile strength and fracture toughness of the SiCf-SiC composites were also studied. The SiCf-SiC composites were subjected to thermal exposure (1000°C for 100 hr in an oxidizing atmosphere) and tensile strength results obtained before and after thermal exposure were compared. RT Flexural Strength and Fracture Toughness (KIC) of composite-SQAV (SiCf/C/SiC) and composite-SQBII ( SiCf/BN/SiC ) are measured by 3-point bending and results were compared. RT Flexural strength of Cf-SiC composites with C interface of two thicknesses were measured and

Abstract: Surface and interfacial properties of borosilicate glass/ceramic systems have been investigated using the sessile drop method. The purpose is to compare and understand the reactivity of the sealing glass in C / SiC and SiC / SiC composites. A hot wall reactor has been designed to measure the variation of the contact angle and the spreading kinetic according to the temperature (500 to 1100°C) and the atmosphere (Ar, Ar + O2 and Ar + H2O). Chemical and morphological analyses underline (i) the strong reactivity between the liquid and the ceramic, (ii) the influence of the infiltration process and (iii) the strong influence of the oxidizing agent on the wetting behaviour of the glass/ceramic systems.

Abstract: Ceramic matrix composites (CMCs) have evolved as potential candidate materials for high-temperature structural applications due to lightweight, high-temperature strength and excellent corrosion and wear resistance. In this investigation, damage evolution and heat generation of CMCs during monotonic loadings were investigated using different types of nondestructive evaluation (NDE) techniques, such as acoustic emission (AE) and infrared (IR) thermography and microstructural characterization. IR camera was used for in-situ monitoring of temperature evolution, and the temperature changes during testing were measured. A significant temperature increase has been observed at the time of failure. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture behavior of CMC samples. In this investigation, the NDE technique and SEM characterization were employed to analyze damage evolution and progress of ceramic matrix composites during monotonic loading.