Authors: Xin Gang Luan, Lai Fei Cheng
Abstract: To understand the creep damage mechanism of a standard 3D Carbon fiber reinforced silicon carbide composite (C/SiC) in high temperature combustion gas at 1300 °C, the creep tests were carried out in a combustion wind tunnel and the mechanisms were investigated by the extension of specimens and the microstructure of fracture section. It was found that the external tensile load was bore by the carbon fibers in the active region during the stressed oxidation process. The oxidation mechanisms of the active region were determined by a normalized threshold stress. Below the normalized threshold stress, the oxidation was controlled by internal diffusion of oxidizing gases through microcracks in SiC matrix. Above the normalized threshold stress, the oxidation was controlled by the reaction of carbon fiber with oxygen and water vapor.
802
Authors: Cao Wang, Zhe Zhao, Lai Fei Cheng
Abstract: A finite element model (FEM) is developed to simulate the temperature distribution in the sample/die/punch assembly during the spark plasma sintering (SPS) process. A thermal–electrical coupled model with temperature dependent thermal and electrical properties is implemented. The simulation studies were conducted using COMSOL and a range of heating-rates and die sizes were considered. Also, both temporary and equilibrium condition during heating process were evaluated in order to express the real temperature development in the sintering. During the spark plasma sintering process, the temperature difference between the sample center and the die surface depend on the heating-rate and die size. The simulation results also revealed that the temperature gradient during the heating process is much bigger than that in the dwelling period. It is necessary to consider the temporary state during the spark plasma sintering process in order to guarantee a well–controlled microstructure, especially in non-conductive ceramic materials.
808
Authors: Jian Zhang Li, Jun Zhang, Li Tong Zhang, Lai Fei Cheng, Yong Dong Xu
Abstract: Carbon fiber reinforced silicon carbide matrix composites (C/SiC) are promising candidate
materials for high-temperature structural applications. However, in oxidizing environments the two
main constituents, that is, carbon fiber and pyrolytic carbon interphase which bears and transfers
loads respectively are susceptible to deplete rapidly for oxidation. In this paper, the oxidation
behavior of carbon fiber and pyrolytic carbon were investigated by simulating environmental
experiments and scanning electron microscopy. The reactivity discrepancy in the carbonaceous
constituents and in the different zone of carbon fiber was discerned. After oxidation, the morphology
of carbon phase broken before oxidation were compared with that of those broken after oxidation.
Based on the microstructural model, the contrast results of morphology were well interpreted from
the reactive preference and selectivity.
43
Authors: Jian Zhang Li, Li Tong Zhang, Lai Fei Cheng, Yong Dong Xu, Sheng Ru Qiao, Gui Qiong Jiao, Jun Zhang, Xin Gang Luan
Abstract: Materials characterization is a crucial issue in the development and application of new
materials. Materials characterization aims to mine and acquire characteristic information and their
evolution in the materials. It mainly includes three important topics which are microstructural
characterization, properties characterization, and environmental degradation. In this paper,
characterization techniques about these topics were discussed for C/SiC composites and a
characterization system was preliminarily established. All these characterization research and their
results further the better understanding of the relationship between microstructure and properties
and of the failure mechanisms in the C/SiC composites.
31
Authors: Peng Fang, Lai Fei Cheng, Li Tong Zhang, Hui Mei, Jun Zhang
Abstract: Three-dimensional (3D) carbon fiber reinforced silicon carbide matrix composites (C/SiC)
were prepared by a low-pressure chemical vapor infiltration method. The thermal shock behaviors of
the composites in different environments were researched using an advanced acoustic emission (AE)
system. Damage initiation and propagation were easily detected and evaluated by AE. The thermal
shock damage to C/SiC composites mainly occurred at the process of cooling and was limited at argon
but unlimited at wet oxygen atmosphere. Also correlations have been established between the
different damage mechanisms and the characteristics of acoustic emission signals obtained during
thermal shock tests. In this way, the paper contributes to the development of the acoustic emission
technique for monitoring of damage development in ceramic-matrix composites.
1585
Authors: Qing Zhang, Lai Fei Cheng, Wei Wang, Xi Wei, Li Tong Zhang, Yong Dong Xu
Abstract: Internal friction of 2D C/SiC composites fabricated by chemical vapor infiltration (CVI)
method was measured by dynamical mechanical analysis (DMA) at different frequencies from room
temperature (RT) to 400°C in air atmosphere. Internal friction of 2D C/SiC composites increased
gradually with increasing temperature and then decreased after damping peak appeared in the
temperature range of 250°C to 300°C. Damping capacity and peak value decreased gradually with
increasing frequency, accompanied with a shift of damping peak towards lower temperatures.
Moreover, the effect of interphase thickness on damping behavior of 2D C/SiC composites was
investigated. The results showed that damping peak of the composites increased gradually and the
temperature of the peak shifted to the lower temperature with increasing PyC interphase thickness,
when the interphase thickness is in the range of 90~296nm. The influence of interphase thickness on
interfacial bonding strength, sliding resistance and the microstructure of SiC matrix was discussed,
which was considered to be responsible for the results.
1531
Authors: Xian Zhang, Lai Fei Cheng, Li Tong Zhang, Shou Jun Wu, Yong Dong Xu
Abstract: Nano-yttria powder can be synthesized by yttrium citrate-urea precursor, combusted at
600°C in air. The CVD SiC coated on graphite (CVD SiC/Graphite) infiltrated by the yttrium
citrate-urea precursor, combusted at of 600°C, and then sintered at 1450°C, the thin yttria film can
be achieved. The SEM morphology and EDS result of the thin yttria film show a mass of
needle-shaped pining into the CVD SiC layer, which improves the combination of CVD SiC
layer and wash yttria coating. Therefore, it is an effective transition layer between CVD SiC
coating and wash yttria layer.
653
Authors: Li Tong Zhang, Lai Fei Cheng, Xin Gang Luan, Hui Mei, Yong Dong Xu
Abstract: The conventional ultimate performance test by applying a component in its true
application (i.e., in an engine) is often very expensive and impractical when dealing with developmental materials. Simpler, less expensive, and more practical test methods must be utilized. The present work aims toward the applications of an innovative methodology for testing environmental performance of advanced Ceramic Matrix Composites (CMCs) in the presence of combined mechanical, thermal, and environmental applied conditions. To obtain a comprehensive understanding of how a composite might perform in certain application environments, a newly developed environmental performance testing system, which is able to provide the fundamental
damage information of the composites in simulating service environments including variables such as temperature, mechanical and thermal stresses, flowing oxidizing gases and high gas pressure, is proposed. The system comprises of two subsystems: (1) equivalent experimental simulating subsystem, and (2) wind tunnel experimental simulating subsystem. The evolution mechanisms of
the composites properties and microstructures can be achieved by the former, and then be validated and modified by the latter. Various loading (e.g. fatigue, creep), various atmospheres (e.g. argon, oxygen, water vapor, wet oxygen and molten salt vapor) and various temperature conditions (e.g. constant or cyclic temperatures) can be conducted on the system. Some typical experimental results
are presented in this paper. Large quantities of tests have demonstrated the extraordinary stability and reliability of the system.
183
Authors: Q.F. Zeng, Lai Fei Cheng, Li Tong Zhang, Xin Gang Luan
339
Authors: Li Tong Zhang, Lai Fei Cheng, Xin Gang Luan, N. Dong
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