Journal of Powder Materials

An Overview of The Commercialisation of The Spray Forming Process: Alan Leatham; J Korean Powder Metall Inst. 1996;3(4):227-232.

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Abstract PDF: (i) The development of a metallurgical bond during the spray forming of clad products has offered the possibility of manufacturing large rolls, including those used in hot and cold strip mills. Small rolls are already being produced in Japan. (ii) Technical developments, including the use-of-multi-atomizers have resulted in the elimination of porosity from the internal bore of a sprayed tube. Bimetallic tubing can also be manufactured and the installation of a 4.5 ton tube plant in the USA should provide low operation costs. (iii) Spray forming offers a potentially low cost manufacturing route for superalloy ring/casing components in high strength superalloys. (iv) A large pilot plant has been built for the spray forming of ultra-clean superalloys for turbine disc applications. (v) Using twin-atomizing technology, special steel billets have been spray formed up to 400mm diameter with deposition yields in excess of 90%. (vi) Al/Si alloy extrusion billets with excellent dimensional tolerances are being manufactured for large scale automotive applications. Several new aluminum alloys have also been developed, including high strength, low density and low cocfficient of expansion materials. (vii) New copper alloys have been developed and pilot plants are in operation to produce these alloys once markets have become established.

Nanocrystalline Materials-an Overview: C. Suryanarayana; J Korean Powder Metall Inst. 1996;3(4):233-245.

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Abstract PDF: Nanocrystalline materials, with a grain size of typically <100 nm, are a new class of materials with properties vastly different from and often superior to those of the conventional coarse-grained materials. These materials can be synthesized by a number of different techniques and the grain size, morphology, and composition can be controlled by controlling the process parameters. In comparison to the coarse-grained materials, nanocrystalline materials show higher strength and hardness, enhanced diffusivity, improved ductility/toughness, reduced, density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher coefficient of thermal expansion, lower thermal conductivity, and superior soft and hard magnetic properties. Limited quantities of these materials are presently produced and marketed in the US, Canada, and elsewhere. Applications for these materials are being actively explored. The present article discusses the synthesis, structure, thermal stability, properties, and potential application of nanocrystalline materials.

Thermoelectric Properties of p-type 25% Bi_2Te_3+75%Sb_2Te_3 Materials Prepared by Rapid Solidification Process and Hot Pressing: J Korean Powder Metall Inst. 1996;3(4):246-252.

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Abstract PDF: Bi_2Te_3-Sb_2Te_3, Bi_2Te_3-Bi_2Se_3 solid solutions are of great interest as materials for thermoelectric energy conversion. One of the key technologies to ensure the efficiency of thermoelectric device is to obtain chemically homogeneous solid solutions. In this work, the new process with rapid solidification followed by hot pressing was investigated to produce homogeneous thermoelectric materials. Characteristics of the materials were examined with XRD, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as excess Te quantity and hot pressing temperature. Quenched ribbons are very brittle and consisted of homogeneous Bi_2Te_3, Sb_2Te_3 solid solutions. When the process parameters were optimized, the maximum figure of merit was 3.073times10-3K-4. The bending strength of the material, hot pressed at 450°C, was 5.87 kgf/mm2.

Thermoelectric Properties of n-type 90%Bi_2Te_3+10% Bi_2Se_3 Materials Prepared by Rapid Solidification Process and Hot Pressing: J Korean Powder Metall Inst. 1996;3(4):253-259.

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Abstract PDF: The efficiency of thermoelectric devices for different applications is known to depend on the thermoelectric effectiveness of the material which tends to grow with the increase of its chemical homogeneity. Thus an important goal for thermal devices is to obtain chemically homogeneous solid solutions. In this work, the new process with rapid solidification (melt spinning method) followed by hot pressing was investigated to produce homogeneous material. Characteristics of the material were examined with HRD, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as dopant CdCl_2 quantity and hot pressing temperature. Quenched ribbons are very brittle and consist of homogeneous Bi_2Te_3, Bi_2Se_3 solid solutions. When the process parameters were optimized, the maximum figure of merit was 2.038times10-3K-4. The bending strength of the material hot pressed at 500°C was 8.2 kgf/mm2.

Finite Element Analysis for Extrusion of Rapidly Solidified Al-Si Alloys: J Korean Powder Metall Inst. 1996;3(4):260-265.

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Abstract PDF: Investigation on the extrusion of rapidly solidified Al-Si alloys was performed in order to develop an inexpensive production process of high strength parts. It is necessary to establish optimum process variables for the extruding condition through the experiments, because it is high cost and time consuming process. In this paper, the experimental results was compared to the finite element analysis for the extrusion of rapidly solidified Al-Si alloys. The results of this simulation helped to understand the distribution of relative density and effective stress for rapidly solidified Al-Si alloys during the extrusion process. This information is expected to assist in improving the extrusion operations of rapidly solidified Al-Si alloys.

Microstructure Evolution in the Layered (WC-Co)/Fe Powder Compacts with a Composition Gradient during Vacuum Sintering: J Korean Powder Metall Inst. 1996;3(4):266-270.

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Abstract PDF: The microstructure evolution during sintering of a compact being composed of three layers of (WC-15%Co)/Fe powder mixture with different Fe contents has been observed. The Fe contents in the respective (WC-15%Co)/Fe layers were varied by 20%. 50%, and 90% in sequence by volume from a top layer to a bot- tom layer. The sintering temperatures and times were varied from 1100°C to 1250°C and from 1 h to 4 h, The compact layer was not densified below 1200°C in 4 h. Appropriate sintering temperature and time conditions for making a multi-layered hard metal compact were determined as 1250°C and 3 h, respectively.

The Relationship between Microstructure and Property of Rapidly Solidified Al-Mg-X(X=Cr, Zr or Mn) Asloys: J Korean Powder Metall Inst. 1996;3(4):271-278.

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Abstract PDF: In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al-Mg-X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 mum were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively large particles occasionally at grain boundaries. The ultimate tensile strengths of Al-Mg-X alloys were found to decrease rather remarkably at 150 °C without the gain of the ductility at 150 °C, which may result from segregation of beta (Al_3Mg_2) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed upon alloy systems. The ductility at 530 °C was found to be ~100%, suggesting that grain boundary sliding did not contribute to ductiliy despite he grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al-Mg-X alloys.

기계적 합금화의 FeSi_2계 열전재료 개발에의 응용: J Korean Powder Metall Inst. 1996;3(4):279-281.

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