Papers by Author: Byoung Kee Kim

Abstract: Ni59Zr20Ti16Si2Sn3 bulk metallic glass (BMG) powders were produced by a gas atomization process, and ductile Cu powders were coated on the Ni-based BMG powders using a spray drying process in order to increase the ductility. Characteristics of the as-prepared powders with the atomization and spray drying process conditions were investigated. The atomization was conducted at 1450oC under the vacuum of 10-2 torr and the powders were mixed with water-soluble Cu nitrate. The mixture was sprayed at the temperature of 130oC to prepared initial powder. After reduction treatment, sub-micron size Cu powders were successfully coated on the surface of the atomized Ni BMG powders.

Abstract: Magnetic oxide-coated iron nanoparticles with the mean size ranging from 6 to 75 nm were synthesized by aerosol method using iron carbonyl as a precursor under the flowing inert gas atmosphere. Oxide shells were formed by passivation of as-prepared iron particles. The influence of experimental parameters on the nanoparticles’ microstructure, phase composition and growth behavior as well as magnetic properties were investigated and discussed in this study.

Abstract: The paper represents an experimental study of the burr formation mechanism in feed direction. The influence of tool angles and workpiece angles, as well as and other cutting conditions on burr dimensions is considered. The work contains experimental graphs of burr cross-sections obtained using a laser measurement system at various stages of burr formation. The analysis of the experimental work shows that, depending on the cutting conditions, a few mechanisms of burr formation can be distinguished. The study could be useful in the search for optimal tool geometry for burr minimization and for the modeling of a burr formation mechanism.

Abstract: Iron and its nitride (e-Fe3N) nanoparticles were fabricated by the CVC using Fe(CO)5 precursor without the aid of LN2 chiller. The iron particles synthesized at 400 oC were a mixture of amorphous and crystalline a-Fe. Fully crystallized iron particles were then obtained above 600 oC. Iron-nitride particles that were easily formed at 500 oC at 1 atm., however, were not fully developed in vacuum unless the reaction temperature reached 850 oC. Nevertheless, the work chamber needed to be maintained in vacuum to obtain finer iron-nitride particles. The synthesized particles possessing the core-shell type structure were all nearly spherical and enclosed with Fe3O4 or Fe3O4-related amorphous layer. The iron nanoparticles (~20 nm) synthesized at 600 oC at 760 torr exhibited iHc ~ 1.0 kOe and Ms ~ 170 emu/g, whereas the iron-nitride particles (~20 nm) synthesized at 850 oC at 0.01 torr exhibited iHc ~ 0.45 kOe and Ms ~ 115 emu/g.

Abstract: Nanosized Fe based powders have been synthesized by both chemical vapor condensation (CVC) and plasma arc discharge (PAD) processes. Fe, Fe-C and Fe-N nanopowders were successfully synthesized. The influence of experimental parameters on microstructures and phase composition of nanopowders was investigated. The prepared powders were nearly spherical in shape and core-shell type in structure. Various kinds of Fe-C and Fe-N composite nanopowders could be synthesized by controlling the carrier gas and precursor decomposition temperature, etc.

Abstract: Wire cutting(EDM) or blanking is used to made workpieces from sheet metal. Wire EDM provides a relatively simple method for making holes of any desired cross section in material. But EDM requires a lot of working time and the high unit cost of production. In conventional blanking, for the production of precision devices or assemblies, it is always necessary that at least two, but generally more, secondary operations are required per piece part. Using the fine blanking process, a precise finished part with inner and outer forms clearly sheared over the whole material thickness are produced in one single operation. In this study an attempt is made to manufacture a sprocket with fine blanking process. The sprocket is parts for the tape feeder of surface mount system in electronic parts. First, a change of the existing design is made in a sprocket. The materials selected are three kinds of stainless steel, SUS304, SUS316 and SUS430. And the mechanical properties are investigated through the tensile test. After fine blanking, hardness and precision are examined with hardness test and 3-dimensional coordinate measuring for samples. The results of investigations of fine-blanking process with the help of FEM code, DEFORM 2D, are presented. For the simulation, SUS304 and SUS316 are used as materials. The damage model of Cockroft and Latham is used to calculate damage. Die-roll height, die-roll width, burnish zone and fracture zone from the fine blanking simulation are investigated in comparison with them of samples. And the applied force at each part of fine-blanking die is estimated with load-stroke diagram.

Abstract: Effect of washing step in R-D process on the structure and magnetic properties of Nd-Fe-B powder fabricated by the process using a spray-dried precursor was investigated. Although the powder washed in water contained much more residual CaO than that washed in dilute acetic acid, magnetic properties of the former were much better than those of the latter due to less removal of Nd-rich phase. In the powder washed in water Nd2Fe14B particles were enclosed with thin layer of Nd-rich phase, and each particle consisted of one or more subgrains of the size 50 ~ 100 nm or more. Milling the powder before water washing was effective to remove more CaO, thereby increased the remanence of the powder.