Papers by Author: Won Wook Park

Abstract: The magnetic inductance of nanocrystalline Fe73Si16B7Nb3Cu1 and an amorphous FeSiB sheet has been investigated to identify the radiofrequency identification (RFID) performance. Planar flow cast amorphous ribbons were pulverized and classified using a stack of sieve. The powder was mixed with binder and solvent and tape-casted to form 0.6-0.8 mm thick films. The inductance of the sheet was measured to investigate the RFID characteristics of the nanocrystalline and the amorphous materials. Results showed that the atmosphere for annealing significantly influenced on the inductance of the material. The surface oxidation of the particles was the main reason for the reduced inductance. The maximum inductance of Fe73Si16B7Nb3Cu1 alloy was about 88μH at 17.4 MHz, which was about 65% greater compared to the amorphous FeSiB alloy. The higher inductance in the nanocrystalline alloy indicates that it may be used as a potential replacement of current RFID materials.

Abstract: AZ31 magnesium plates with 1mm in thickness were fabricated by casting and subsequent hot rolling process. Both wheel-band continuous casting (modified Properzi) and horizontal continuous casting (HCC) machine were designed and employed to produce AZ31 alloy plates. The plates with 5x50mm in size produced by modified Properzi process exhibited good surface qualities that were sustained during following rolling process. Surface qualities of HCC plates with 120x30mm in size were very sensitive depending on the processing parameters. Homogenization treatment or surface machining before rolling was effective to get good thin plate. By means of rolling process, microstructures were refined effectively to the size of 7~10µm.

Abstract: The effect of heat treatment and binder additions on the magnetic behavior of P/M(powder metallurgy) processed Fe_73.5Si_13.5B₉Cu₁Nb₃ alloy has been investigated. FeSiBCuNb amorphous ribbons produced by plannar flow casting were annealed at temperatures between 480°C and 620°C for 20 to 60 minutes. The annealed specimens were milled using a pin crusher and a hammer mill. The powder was then mixed with mineral or polymer binders to press into a toroidal shape of inductor core at room temperature. Fe_73.5Si_13.5B₉Cu₁Nb₃ alloy showed maximum permeability when annealed at 540°C for 40 minutes. The microstructure of the annealed ribbon has a ultra-fine α-Fe(Si) grain, ranging from 10 to 20 nm in diameter. Inductor cores produced using a glass binder showed better magnetic properties than polymers or oxide binders. The use of mineral binders in producing nanocrystalline inductor cores significantly improved magnetic properties, compared to a commercial moly-permalloy powder core.

Abstract: The liquid oxidation behavior of Mg-Ca base alloys containing Be has been presented in this paper. The ignition temperature test and microbalance measurement indicated that the oxide film formed at elevated temperature was protective, resulting in the improved oxidation resistance and ignition-proof properties. A Ca-rich zone was found at the very near surface of oxide layer. With Be addition the oxide layer became dense and compact, which was impermeable for the rapid diffusion of oxygen and magnesium through the oxide layer. It was concluded that the formation of BeO in the oxide layer suppressed the continuous growth of the oxide layer.