Preparation, Microstructure and Properties of Silicon Nitride Ceramics with Aligned Whisker Seeds

D. S. Park et al., "Preparation, Microstructure and Properties of Silicon Nitride Ceramics with Aligned Whisker Seeds", Key Engineering Materials, Vol. 237, pp. 175-184, 2003

Online since:

April 2003

Authors:

Dong Soo Park, Byung Chan Bae, Byung Dong Han, Hai Doo Kim, Chan Park

Keywords:

Alignment, Core-Rim, De-Wetting, Microstructure, Modified Tape Casting, Wear, Whisker Seeds

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References

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[6] H. Imamura, K. Hirao, M.E. Brito, M. Toriyama and S. Kanzaki, J. Am. Ceram. Soc., 83 (2000) 495.

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[9] M. Zenotchkine, R. Shuba, J. S. Kim and I-W. Chen, J. Am. Ceram. Soc., 84 (2001) 1651.

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[12] G.B. Jeffery, Proc. R. soc. London, A, 102 (1922) 161.

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Paper TitlePages

Semi-Solid Forming of Al-Mg-Zn Based High Strength Alloys

Authors: Jeong Min Kim, Ki Duk Seong, Joong Hwan Jun, Ki Tae Kim, Woon Jae Jung

Abstract: Semi-Solid Al-5%Mg-3%Zn-1%Mn alloys with or without 0.2%Zr were prepared by the isothermal heating of either cast ingot or extruded billet. The microstructural and tensile properties variations during the isothermal heating, depending on alloy composition and slurry preparation method, were investigated. The grain (globule) size of semi-solid microstructure was not remarkably changed by the slurry preparation method, however it was significantly reduced by the Zr additions. The room temperature tensile elongation of the semi-solid formed alloys was generally higher in case of the extruded billet. T6 heat treatment was not found effective in improving the strength of the semi-solid alloys, unlike the casting alloys.

284

A Novel Green Tape with High Solid Content Prepared by Aqueous Tape-Casting

Authors: Shuang Xi Wang, Xue Qiong Ouyang, Ya Dong Wang, Qiong Na Zheng, Jing You

Abstract: Green tapes were prepared by aqueous tape-casting method with binders of polyvinyl alcohol, styrene-acrylate emulsion and the mixed binders, respectively. Effects of solid content and binders on viscosity of the slurry were investigated by digital rotary viscosimeter. Results show that solid content should be lower than 60wt % with the binder of PVA; solid content could achieve the maximum 73wt% by tape-casting using emulsion as binder. Furthermore, slurry with solid content up to 75wt % had been successfully prepared by tape-casting using mixed binders. Mixed binders are promising additives to produce high solid content green tapes with smooth surface, adequate strength and very good flexibility.

646

Research on the Preparation and Rheo-Casting of A356 Al Alloy by LSPWES Process

Authors: Man Huan Li, Guo Xing Tang, Wei Min Mao, Yong Feng Liu

Abstract: The semisolid slurry of A356 Al alloy was prepared by low superheat pouring and weak traveling-wave electromagnetic stirring (LSPWES), and then the slurry was further soaked for proper time and finally rheo-cast into a rheo-casting sample in this paper. The experimental results show that if the melt of A356 Al alloy is poured at 630-650°C and meanwhile stirred by weak electromagnetic field for a short time, the most primary α-Al grains solidified in the slurry are spherical and only a few are rosette-like. The shape of primary α-Al becomes more spheroidal and more homogeneous distribution in the microstructure by the process of the uniform temperature fields. The experimental results also show that the slurry temperature, injection pressure and speed have a great influence on filling ability. The higher the slurry temperature, injection pressure and speed, the higher the slurry filling ability, the more easily the die cavity is filled. With the given rheo-casting sample, if only the slurry temperature should be equal to or more than 585°C, or the injection pressure is equal to or more than 20 MPa, or the injection speed should be equal to or more than 0.24m/s, the rheo-casting sample die cavity can be filled completely. The microstructure of the castings indicates that the shape, size and numbers of the primary α-Al grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 160 °C for 16 h, the tensile strength, elongation rate and hardness of the rheo-casting samples with the above process are respectively 321.5 MPa, 8.03% and 105.9HB.

Numerical Simulation and Die Casting Process for Cylinder

Authors: Yong Huang, Yue Dong, Xiao Ming Du

Abstract: Filling and solidification for aluminum alloy packing block in die casting were simulated by numerical simulation. Distribution and change of temperature field as well as velocity field were visualized. The desirable processing parameters can be obtained with pouring temperature of 620°C and mould temperature of 180°C as well as shot velocity of 4m/s. The qualified products were obtained on the basis of the optimized die-casting parameters.

2362

Shape Forming of Alumina by Step Pressure-Vacuum Hybrid Slip Casting

Authors: Kyeong Sik Cho, Jae Kim, Seung Yeul Lee, Joong Pyo Oh, Seung Il Park

Abstract: Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates, because of disadvantages such as the high cost of equipment, formation of density gradient, and differential shrinkage during drying. These problems could be avoided by employing step pressure-vacuum hybrid slip casting in which consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium (water) around the mold. This method enabled us to fabricate a 110 × 110 × 20 mm alumina plate without cracks and with homogenous density, and the possibility of extending the method to fabricate other ceramic products appears to be promising.

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