Designing, Processing and Properties of Advanced Engineering Materials

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Authors: Veeramuthu Vaithianathan, Jung Ho Je, Byung Teak Lee, Sang Sub Kim
Abstract: Growth behavior of Mn-doped ZnO thin films (Zn1-xMnxO) onAl2O3 (0001) substrates by pulsed laser deposition was investigated as a function of Mn content (0.00≤x≤0.35) mainly using synchrotron x-ray diffraction. We found that a small amount of Mn doping (x=0.05) significantly improves the crystalline quality, and also leads to a singly oriented film. The superior epitaxial growth of the film with an optimum Mn content seems to be associated with its microstructural evolution.
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Authors: Yang Do Kim, Jang Hee Lee, Jae Hyoung Koo, Ho Jung Chang, Hyeong Tag Jeon
Abstract: ZrO2/Al2O3 bilayer structure was investigated as one of potential replacements for SiO2 gate dielectric. Al2O3 and ZrO2 films were also examined and showed stoichiometric characteristics with negligible chlorine and carbon impurities. Al2O3 film exhibited an amorphous structure without interlayer formation while ZrO2 film showed a randomly oriented polycrystalline structure with amorphous phase of interlayer. ZrO2/Al2O3bilayer film exhibited no interfacial layer between Si substrate and Al2O3 layers. The flat band voltage and hysteresis of ZrO2/Al2O3bilayer film were 0.8 V and 150 mV, respectively, with fully reversible hysteresis. The measured leakage current of ZrO2/Al2O3bilayer film was 1.2E-6 A/cm2 with EOT value of 1.4 nm. ZrO2/Al2O3 bilayer film showed significantly enhanced gate oxide properties compared to those of the individual Al2O3 and ZrO2 films.
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Authors: Hee Jin Kim, Yong Sul Song, Won Wook Park, Keun Yong Sohn
Abstract: The effect of heat treatment and binder additions on the magnetic behavior of P/M(powder metallurgy) processed Fe73.5Si13.5B9Cu1Nb3 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. Fe73.5Si13.5B9Cu1Nb3 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.
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Authors: Dong Hwan Kim, Andrew S. Kim, Sang Myun Kim, Tae Suk Jang
Abstract: A new axial pressing method using pulse magnetizing field was studied to improve the remanence of Nd-Fe-B sintered magnets. In pulsed axial die pressing(PADP) process , tapping density of powders, method of pulse supply and strength of pulse field were optimized to increase magnetic alignment and remanence. As a results, we could find that an axial pressing under pulse magnetizing field was very effective to increase the degree of magnetic alignment of powder, yielding remanences even higher than those obtained by the transverse die pressing. The remanence of 14.1 kG was easily obtained by PADP process from 31R-68TM-1B (in wt.%) sintered magnet
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Authors: Hyun Jung Kim, In Chang Song, Jae Ho Sim, Hyo Jin Kim, Do Jin Kim, Young Eon Ihm, Woong Kil Choo
Abstract: We report on the effect of the oxygen partial pressure ratio in the sputtering gas mixture on the electrical and magnetic properties of cubic spinel ZnCo2O4 thin films grown by reactive magnetron sputtering. The conduction type and carrier concentration in ZnCo2O4 films were found to be dependent on the oxygen partial pressure ratio. The maximum electron and hole concentration at 300 K were estimated to be as high as 1.37 × 1020 cm-3 and 2.81 × 1020 cm-3, respectively. While an antiferromagnetic coupling was found for n-type ZnCo2O4, a ferromagnetic interaction was observable in p-type ZnCo2O4, indicating hole-induced ferromagnetic transition in spinel ZnCo2O4.
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Authors: Ku Hyun Kang, Sung J. Lee, Seung Eui Nam, Hyoung June Kim
Abstract: We propose a new method for lower process temperature and shorter process time of SPC. This method involves the induction of high frequency alternating magnetic field during crystallization annealing, referring this process as Alternating Magnetic Field Crystallization, AMFC. The processed films were characterized using UV spectroscopy to determine the incubation time, Raman spectroscopy for the degree of crystallization. We found that the kinetics of crystallization was greatly enhanced by alternating magnetic field. When we crystallized, in the case of SPC, annealing time is over 14 hours at 570°C. But in the case of AMFC, annealing time is only 20minutes at the same temperature.
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Authors: In Gon Kim, Yang Do Kim, In Bae Kim
Abstract: The effects of pre-strain and aging treatment on the mechanical properties of hot rolled steel sheet containing 1.0wt.%Cu were investigated. As the amount of pre-strain increased, the maximum hardness increased and the time to reach its peak hardness decreased. Tensile strength of 10% pre-strained steel was 600MPa. This value was about 150MPa higher than that of hot rolled steel. In case of 30% pre-strained steel, the strength was further increased to 657MPa. Such a strength increase was due to the strain hardening and enhanced precipitation reaction of Cu-clusters. TEM study revealed that fine Cu-clusters were uniformly dispersed throughout the grain. This means that the precipitation of Cu-clusters was mainly controlled by the vacancies introduced during the pre-straining process. The size of Cu-clusters was about 10~20nm at peak aged condition and they had spherical shape.
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Authors: T. Maebashi, Minoru Doi, Takao Kozakai
Abstract: The morphological changes and the coarsening kinetics of B2 particles in A2 matrix in the elastically constrained Fe-16at%Al-18at%Co alloy were investigated by means of transmission electron microscopy (TEM). The mean particle radius increases in proportion to the cube root of ageing time at early stage, then the coarsening of B2 particle decelerate at late stage of aging. And it clarified the decelerated coarsening in Fe based alloy also is related to the change in PSD and is caused by the elastically strained effect.
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Authors: Yoshikazu Todaka, Minoru Umemoto, Koichi Tsuchiya
Abstract: Deformation and dissolution behavior of the cementite in eutectoid steels with pearlitic and spheroidite structures were studied using high resolution SEM and AFM. Cementite lamellae in deformed pearlite exhibited inhomogeneous slip, smooth thinning or necking, fragmentation and cleavage fracture. Complete dissolution of cementite lamellae and spheroidal cementite particles was observed in specimens deformed with large strains at high strain rates. The dissolution mechanism of cementite by heavy deformation was discussed.
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Authors: Minoru Doi, Daisuke Sakai, Toshiyuki Koyama, Takao Kozakai, Tomokazu Moritani
Abstract: The present study examined the effects of heat treatment and the addition of Cu-Ni alloy on the corrosion resistance of the matrix of spheroidal graphite cast iron in aqueous environments. Test materials of white cast iron and carbon steel were used for comparison with spheroidal graphite cast iron. The alloy spheroidal graphite cast iron that added Cu and Ni was prepared. The spheroidal graphite cast iron was subjected to three kinds of heat treatment to adjust the matrix: annealing, oil quenching, and austemper heat treatment. In electrochemical tests, measurements of corrosion electrode potential and cathode and anode polarization were used. The following was clarified from the relationship between the electrode potential and current density of each of the materials in each of the solution. The alloy spheroidal graphite cast iron had a high corrosion electrode potential owing to the addition of Cu-Ni, and tended to have a low corrosion current density. This demonstrates that in any of the materials having a matrix adjusted by heat treatment, the addition of Cu-Ni increased the corrosion resistance. The corrosion current density was highest in a sulfuric acid environment.
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