Papers by Keyword: SiC Ceramic

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Authors: Zhong Liang Lu, Di Chen Li
Abstract: A free form surface reconstruction method based on least square support vector regression is presented. Firstly in order to eliminate noise points, some sample points are chosen from the measured data to construct LS-SVM model. Thus a LS-SVM model to approximate the measured points is obtained. And the distribution probability of the approximation error is figured out. In result, the noise points are eliminated when their error probability is less than the specified threshold value. Then the boundary points are extracted. Lastly the surface model is reconstructed by use of the measured points from which noise points have been eliminated. The results indicate that the reconstruction precision can satisfy the demands of engineering application.
Authors: Fei Zhou, Koji Kato, Koshi Adachi
Abstract: The tribological behaviors of a-CNx/SiC tribo-pairs in water at low velocity were investigated and compared with SiC/SiC at room temperature. The results showed that the mean value µ of friction coefficients at steady state for a-CNx/SiC tribo-pairs (µ=0.075~0.12) was lower than that of SiC/SiC systems (µ=0.24~0.27). At a constant sliding speed, µ for two kinds of tribo-couples decreased with an increase in normal load, but at a constant normal load, µ for SiC/SiC system was nearly independence of sliding speed, whereas that of a-CNx/SiC tribo-pair decreased with sliding speed. The specific wear rates (ws) of ball and disk for a-CNx/SiC tribo-couples were considerably reduced by a factor up to 10 in the comparison to those of SiC/SiC systems. The observations of wear scars showed that the wear mechanism of CNx coating was micro-fracture of irregularities on the film surface for build-up of tribolayer, while that of SiC/SiC system was dominated by mechanical wear.
Authors: Ke Zhang, Guo Zhi Liu, Hai Yan Gao, Hong Sun, Yu Lan Tang, Yu Lan Tang, Yu Hou Wu
Abstract: SiC ceramics is very promising to be widely applied due to the excellent physical and chemical properties.However, the very difficult process of SiC ceramics hinders its application. In this paper, the nano-cutting of SiC ceramics is simulated based on molecular dynamics. The influences of the tool rake and cutting depth on the cutting force, the kinetic energy and potential are analyzed. The results show that the cutting force, system kinetic energy and potential energy increase firstly,reach the maximum, and then decrease in the process; with the increase of the tool rake, the cutting force and the kinetic energy decrease; with the increase of the cutting depth, the cutting force increases, and the kinetic energy and the potential energy decreases. These results are very helpful to understanding the process mechanism of SiC ceramics and increasing its process efficiency
Authors: Min Hui Liu, Fei Hu Zhang, Guo Dong Lu
Abstract: Silicon carbide ceramics with its excellent physical and mechanical properties have become the preferred material for space large diameter mirror. Diamond wheel grinding is the main way of SiC ceramics forming processing. Subsurface cracks is generated due to the high hardness and brittleness of the material after grinding. In order to remove the impact of cracks, poishing processing with very low efficiency is applied, so it is significant to control the depth of silicon carbide ceramic grinding subsurface cracks and shorten the processing cycle.In this paper grinding experiment of SiC ceramic is conducted. The method of cross-section polishing combined with scanning electron microscope observation is used to research grinding subsurface cracks. The depth of broken surface layer and the maximum depth of sub-surface cracks were proposed to evaluate the grinding subsurface cracks. The result show broken surface layer depth and the maximum depth of sub-surface cracks increase with the decreasement of spindle speed, and increasement of feed rate and grinding depth.
Authors: Dong Yun Li, Guan Jun Qiao, Zhi Hao Jin
Authors: Kyoung Hoon Park, In Kyung Sung, Dong Pyo Kim
Authors: Xiao Chen Gai, Zhi Wei Dong, Qing Liang Zhao, Hong Bin Liu
Abstract: Femtosecond laser micromachining technology shows abroad application background in the field of micro manufacturing due to its unique advantages, especially for micromachining of ultrahard materials such as Silicon carbide (SiC) ceramic. The femtosecond laser micromachining system was set up, by using the system, effects of scanning velocity and laser pulse energy on quality of micromachined features were evaluated. The optimized technological parameter was obtained as 8mW, 1mm/s with 1kHz repetition frequency respectively on the basis of the morphological characteristics and microstructure accuracy. Besides, V-shaped cavity of 300μm depth and 120°angle was generated with layer-by-layer scan machining. Thus femtosecond laser micromachining technology is an effective method for hard and brittle materials precision processing.
Authors: Jian Er Zhou, Xiao Zhen Zhang, Shi Jiang Peng
Abstract: Ca0.6Mg0.4Zr4(PO4)6 coating was used as environmental barrier coatings (EBC) to improve the alkali corrosion resistance of SiC ceramic at high temperature. A new sol-gel based process has been developed for preparing high quality and thick C0.6M0.4ZP coating on SiC ceramic with once deposition. The prepared C0.6M0.4ZP coating on SiC ceramic is homogeneous and dense, and shows a thickness of about 200 μm when sintered at 1400 °C for 3h. The effectiveness of C0.6M0.4ZP coating in improving the alkali corrosion resistance of SiC ceramic was evaluated based on the SEM microstructural analysis, mass change and flexural strength measurements after being subjected to alkali Na-salt attack at 1000 °C for 96 h. Significantly improved alkali corrosion resistance was confirmed for SiC ceramic using C0.6M0.4ZP coating as EBC.
Authors: Yang Wu Mao, Shu Jie Li, Lian Sheng Yan
Abstract: Joining of SiC ceramic to graphite is important from both technical and economical points of view. High temperature brazing of recrystallized SiC ceramic to high strength graphite has been realized using Ni-51Cr (consisting of Ni + 51wt% Cr powders) powders as filler. The obtained maximum three-point bending strength of joints is 32.3MPa, which is equal to 80.8% of the strength of the graphite. Microstructure and phase analysis reveals that interdiffusions and chemical reactions take place in the weld zone. A reaction layer and an interlayer form in the interfacial area. The reaction layer, of which the thickness is about 60-100μm, is contacted with the SiC ceramic. The interlayer with the thickness of about 200μm exists between the graphite and the reaction layer. The reaction layer is mainly composed of Ni2Si, while the interlayer is mainly composed of Cr23C6 and Ni2Si.
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