Composite Materials IV

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Authors: Nyan Hwa Tai, Meng Kao Yeh, Jia Hau Liu, Chien Hsin Yang
Abstract: Composites of phenolic resin reinforced by the multi-walled carbon nanotubes (MWCNTs) were fabricated and its mechanical properties were measured. The MWCNTs were synthesized by the floating catalyst method in a thermal chemical vapor deposition chamber. Benzene, hydrogen, ferrocene, and thiophene were used as carbon source, carrier gas, catalyst, and growth promoter, respectively. The nano-composites were made by the melt mixing and the resin infiltration methods. Tensile strength, Poisson’s ratio, and modulus were measured and the morphologies on the fracture surface were examined by the field emission scanning electron microscope (FESEM). The microstructure of the synthesized MWCNTs reinforced nano-composites was examined by FESEM. The influences of MWCNTs amounts on the mechanical properties of the nano-composites were discussed.
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Authors: Di Zhang, Tong Xiang Fan, Jia Jun Gu, Bing He Sun, Tian Chi Wang, Guo Ding Zhang
Abstract: Morph-genetic synthesis, a preparation method using bio-structures as templates for fabricating micro-cellular materials, has attracted a considerable interest in recent years. In this report, we summarize our obtained results on synthesizing oxides and carbides based on wood templates (for TiC and SiC) and cotton templates (for Al2O3, SnO2 and SiC), respectively. The final products are observed to be faithfully retaining the micro-morphologies of their original natural counterparts, with the template bodies absolutely or partially replaced by the chemically synthesized compounds. These results suggest a new and handy way to fabricate materials with various microstructures, with deliberately choosing desired bio-structures from billions of different species as templates. Moreover, results on Al infiltrated wood templates, as a composite system, are also presented.
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Authors: Xiao Mei Shi, Jian Hua Yang, Yu Bai Pan, Jing Kun Guo
Abstract: Silicon carbide is widely used as an important structural material. It is known for its extreme hardness, high temperature antioxygenic properties and good tribological properties. Moreover, SiC is also an intrinsic semiconductor. SiC can react with AlN and form an extensive solid solution at temperatures between 1800 to 21000C, and has excellent mechanical properties. However, in this article, we study the influence of the microstructure and the dielectric properties of SiC ceramics. SiC-AlN solid-solution ceramics were prepared by hot-pressed sintering using Y2O3 as the sintering additive. The size of SiC and AlN powders were 0.6μm and 1.06µm respectively. The content of AlN starting powders was 14vol%. The hot-processing sintered SiC-AlN multiphase ceramics have reached high density at 1950oC in Ar atmosphere under 30MPa.The hot-processed ceramics were subjected to thermal treatments in a range of temperatures between 11000C and 16000C for 3hr. The grain size increased with the annealing temperature. X-ray diffraction profiles show that phase relationships. Scanning electron microscopy (SEM)) was used to determine fracture surface and the local compositions. Dielectric permittivities and dissipation factor of SiC-AlN composites were investigated with the varieties of annealing temperature and the content of AlN particles. Dielectric constants (ε) and Dielectric loss tangents (tanδ) were measured within the microwave frequency range from 40Hz to10MHz.
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Authors: Tong Xiang Fan, Guang Jun Yang, Jian Qi Chen, Di Zhang
Abstract: This work presents a thermodynamic model to theoretically predict the component activity in multicomponent liquid alloy based on the Wilson equation and an extended Miedema model. Using only the physical parameters of pure metals, the component activities can be theoretically calculated and the calculation results agree well with the measured data. The model should enable very useful predictions to be made for activities in multi-component liquid alloys, especially for the trend of the activity changes with increasing alloy content.
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Authors: Pee Yew Lee, C. Lo, Jason S.C. Jang, J.C. Huang
Abstract: The preparation of Mg49Y15Cu36 metallic glass composite powders was accomplished by mechanical alloying of pure Mg, Y, Cu, and WC powder mixture after 10 h milling. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Mg-based alloy glassy matrix. The metallic glass composites powders were found to exhibit a large supercooled liquid region before crystallization. Bulk metallic glass composites were formed by vacuum hot pressing the as-milled WC/ Mg49Y15Cu36 metallic glass composite powders at 473 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared under pressure of 1.20 GPa. It was found that the applied pressure during consolidation could enhance the thermal stability and promotes nanocrystallization of WC/ Mg49Y15Cu36 BMG composites.
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Authors: Qiu Bao Ouyang, Wen Long Wang, Di Zhang, Guo Ding Zhang
Abstract: Discontinuously reinforced aluminum (DRA) composites are attractive for a large range of engineering applications because of its excellent wear-resistance, high thermal conductivity and light weight etc. In this paper, DRA composites were designed and fabricated especially for automotive application, and their properties were measured. Brake discs of DRA composites were manufactured and their braking performances were investigated, including brake velocity, brake pressure, brake torque, brake deceleration, brake time and surface temperature etc. The test results show DRA composites exhibit an excellent braking performance.
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Authors: Wen Cheng J. Wei, B.Y. Yu, J.F. Li, C.S. Chen
Abstract: SiO2 core/TiO2 shell composite particles were synthesized by four different heterogeneous coagulation techniques. The configurations of the composite particles and the microstructure of assembly were characterized by SEM and TEM. The colloidal stability of nano-particles was also computer-simulated by a discrete element method (DEM) in consideration of Brownian motion occurring on the nano-particles. The results indicated that uniform adsorption of the fine particle absolutely needed fine tuning of surface charging conditions and processing steps.
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Authors: D.B. Luo, H.X. Liu, Shi Xi Ouyang
Abstract: Piezoelectricity of composite was simulated by employing Dilute Model and Limit Unit method. The analogizing results recommend that the particle stackers influence the properties of piezo-composite. While fabricating piezo-composite, particles stack different with different routine. For thermo-pressing proceeding, stackers trend to take on higher D33 than that processing from forging-membrane.
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Authors: Wei Hsing Tuan, S.M. Liu, C.J. Ho, T.J. Yang, Dong Ming Zhang, Lian Meng Zhang, Jing Kun Guo
Abstract: In the present study, the processing-properties relationships of the ZrO2/(Ni+Al2O3) composites are examined. Dense composites were prepared either by pulse electrical current sintering (PECS) at 1350C for 5 minutes or by pressureless sintering (PLS) at 1600C for 1 h. The size of Ni particles is as small as 30 nm to 50 nm. Though the size of ZrO2 grains in the matrix increases as alumina and nickel particles are added, the strength of the ZrO2/(Ni+Al2O3) composites is significantly higher than that of monolithic ZrO2.
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Authors: Yi Wang Bao, V.T. Bublik, Jow Lay Huang, R.H. Sung
Abstract: Mechanical properties of coatings are usually affected by the substrate behavior and the thickness of the coating. The film on a substrate can’t be tested like a monolithic sample. Therefore, the absolute value of the mechanical properties of the film is often difficult to obtain, but the properties of a coated sample and a monolithic sample could be measured, and there must be a unique relation between them. Based on this consideration, a relativity method was proposed to evaluate the mechanical properties of coatings, including the hardness, elastic modulus. Satisfactory results have been obtained from the experiments using this clue. Moreover, residual stresses caused by mismatch of the coefficients of thermal expansion between the coating and substrate was calculated based on the uneven strain mode, it indicates that the interfacial shear stress concentrated at edges and maximum stress in coating is at the center.
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