• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.461-472
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• 1996

The relationship between plastic deformation and crystal grain change in warm forging processes of SM10C carbon steel is studied. If the carbon steel is deformed at warm forging temperature(about recrystallization range), material properties are changed due to microstructural chanre of the crystal grain and cementite of the internal part. Some experimental values are investigated in terms of the elliptic degree of cementite, the grain size of cementite and ferrite grain size. When plastic deformation proceeds, the elliptic degree of cementite becomes larger and the grain size of cementite particle becomes small. In addition, the size of ferrite grain becomes fines by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging was calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result, At the level of effective strain 0.3, dynamic recovery and dynamic recrystallization begin and at the level of over 2.5, the organization of material has better internal structure that is suitable for the following cold forming.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.06a
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• pp.100-123
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• 1995

The relationship between plastic deformation and crystal grain change in warm forging processes of SM100 carbon steel is studied. If the carbon steel is deformed in warm forging temperature (about recrystallization range), the crystal grain and cementite of the internal part are changed, so material properties are changed. Some experimental values, such as the elliptic degree of cementite, the grain size of cementitie and ferrite grain size, are investigated. When the plastic deformation proceeds, the elliptic degree of cementite becomes large, the grain size of cementite particle is small, and the size of ferrite grain appears fine by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging is calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result. At effective strain 0.3 dynamic recovery and dynamic recrystallization begin, over 2.5 the organization of material has better quality that is suitable for the following cold forming.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.272-278
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• 2013

In this study, a c-axis displacement and an internal stress of the sapphire crystal of 300 mm length have been analyzed numerically and the crystal length having no sub-grain defects have been predicted. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The simulation results show that the c-axis displacement difference between the original hot zone and others originated from the sub-grain defect formations in the sapphire ingot. When the crystal grown by CZ (Czochralski) grower using the modified hot zone, the crystal length having no sub-grain defects was increased about 57 mm maximum than the original one. When the simulation results compared with the experimental one, the predicted crystal length having no sub-grain defects were well corresponded with the experiment one in c-axis wafer of the 300 mm sapphire ingot. Therefore the sapphire crystal of 250 mm length having no sub-grain defects was successfully grown by CZ process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.64-72
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• 1998

In this work, we have investigated the change of surface roughness, grain size and crystallinity of Poly-$Si_{1-x}Ge_x$ films deposited with the variation of deposition parameters (temperature, pressure, Ge composition ) and the effect of these results on the electrical resistivity. The crystallinity and the grain size were increased with increasing deposition temperature and Ge composition. Also, the electrical resistivity was decreased by enhanced grain size, while the surface roughness was increased. With increasing deposition pressure, the crystallinity was increased, but the grain size and the cluster size were decreased, by which the surface roughness was decreased. And the electrical resistivity was increased. Based on the effect of the crystallinity and the grain size on the electrical resistivity, it was founded that the electrical resistivity was depend on the grain size rather than the crystallinity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.3
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• pp.638-642
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• 2014

In this study, we investigate on the crystal microstructure and magneto-resistance (MR) change of Bismuth(Bi) thin films for annealing process, in order to apply Bi thin films to the spin electronic devices. As-prepared Bi thin films show the randomly oriented find grains whose size was measured to about 100 nm and the very low MR (4.7 % at room temperature) while careful annealing results in not only grain growth up to ${\sim}2{\mu}m$ but also drastic MR improvement (404 % at room temperature). The drastic change in the MR after applying the annealing process is attributed to the grain growth decreasing grain boundary scattering of electron. Therefore, in this study, we confirm the annealing effect for the grain boundary formation and MR improvement of Bi thin films, and demonstrate the feasibility of spin electronic devices.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.215-220
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• 2004

Molecular Dynamics(MD) method was used to investigate the change of friction force due to interaction between dislocations and a grain boundary when a Ni tip was scratched on a Cu bicrystal. The substrate comprised a Cu bicrystal containing a vertical$\Sigma=5(210)$ grain boundary. The moving tip for scratching simulation was consisted of fixed Ni atoms emulating a rigid tip. The indentation depth was $3.6\AA$ and the scratching was performed along <110>direction in the first grain. As the scratching was continued, nucleation and propagation of dislocations were observed. In the early stage, the grain boundary played as a barrier to moving dislocations and interrupting further dislocation movement with no dislocation resulting in no propagation across the grain boundary. As the Ni tip approached the grain boundary, dislocations were nucleated at the grain boundary and propagated to the second grain. However, stick-slip phenomena that were observed on a single crystal scratching were not observed in the bicrystal. And, instead, irregular oscillation of friction force was observed during the scratching due to the presence of a grain boundary.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.558-563
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• 1996

Fracture strength of $Si_{3}N_{4}/20$ vol% SiC nanocomposites with fifferent sintering additives was measured. Strength of nanocomposites with 6 wt% $Y_{2}O_{3}$ and 2 wt% $Al_{2}O_{3}$ as sintering additives was higher at room temperature but significant strength degradation at elevated temperature was occured due to the softening of grain boundary phase. Fracture strength of 8 wt% $Y_{2}O_{3}$ doped sample was higher than that of $Al_{2}O_{3}$ added sample at $1400^{\circ}C$. The retention of high temperature strength in 8 wt% $Y_{2}O_{3}$ doped sample can be attributed to high softening temperature and crystallization of grain boundary glassy phase.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.841-848
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• 1994

The sintering behavior of La-modified PbTiO3 ceramics was investigated in order to improve the poor sinterability of PbTiO3. Addition of La improved the sinterability. It was confirmed that this improvement was due to the decrease in tetragonality ratio c/a of crystal lattice. The variations of dielectric constant and pyroelectric coefficient were measured with temperature. It was observed that with the increase of La content, Curie temperature decreased and dielectric constant at room temperature increased. La-modified PbTiO3 ceramics had smaller pyroelectric figure of merits than those of pyroelectric materials in use. The effects of grain size on dielectric and pyroelectric properties were also investigated. The change of grain size had effect on maximum dielectric constant and pyroelectric coefficient, but is had little effect on pyroelectric figure of merit at room temperature. The closer examination near ferro-paraelectric phase transition temperature revealed that the behavior of phase transition approached a more relaxor character with the increase of La content and the decrease of grain size.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.251-252
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• 2012

Recently, the growing interest in organic microelectronic devices including OLEDs has led to an increasing amount of research into their many potential applications in the area of flexible electronic devices based on plastic substrates. However, these organic devices require a gas barrier coating to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency OLEDs require an extremely low Water Vapor Transition Rate (WVTR) of $1{\times}10^{-6}g/m^2$/day. The Key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required ($1{\times}10^{-6}g/m^2$/day) is the suppression of defect sites and gas diffusion pathways between grain boundaries. In this study, we developed an $Al_2O_3$ nano-crystal structure single gas barrier layer using a Neutral Beam Assisted Sputtering (NBAS) process. The NBAS system is based on the conventional RF magnetron sputtering and neutral beam source. The neutral beam source consists of an electron cyclotron Resonance (ECR) plasma source and metal reflector. The Ar+ ions in the ECR plasma are accelerated in the plasma sheath between the plasma and reflector, which are then neutralized by Auger neutralization. The neutral beam energies were possible to estimate indirectly through previous experiments and binary collision model. The accelerating potential is the sum of the plasma potential and reflector bias. In previous experiments, while adjusting the reflector bias, changes in the plasma density and the plasma potential were not observed. The neutral beam energy is controlled by the metal reflector bias. The NBAS process can continuously change crystalline structures from an amorphous phase to nano-crystal phase of various grain sizes within a single inorganic thin film. These NBAS process effects can lead to the formation of a nano-crystal structure barrier layer which effectively limits gas diffusion through the pathways between grain boundaries. Our results verify the nano-crystal structure of the NBAS processed $Al_2O_3$ single gas barrier layer through dielectric constant measurement, break down field measurement, and TEM analysis. Finally, the WVTR of $Al_2O_3$ nano-crystal structure single gas barrier layer was measured to be under $5{\times}10^{-6}g/m^2$/day therefore we can confirm that NBAS processed $Al_2O_3$ nano-crystal structure single gas barrier layer is suitable for OLED application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.6
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• pp.518-523
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• 2002

The influences of ion beam energy and reactive oxygen partial pressure on the physical and crystallographic characteristics of transition metal oxide compound(CrOx) film were studied in this paper. Chromium oxide films were deposited onto a cover-glass using ion Beam Sputter Deposition(IBSD) technique according to the various processing parameters. Crystallinity and grain size of as-deposited films were analyzed using XRD analysis. Thickness and Resistivity of the films were measured by $\alpha$-step and 4-point probe measurement. According to the XRD, XPS and resistivity results, the deposited films were the cermet type films which had crystal structure including amorphous oxide(a-oxide) phase and metal Cr phase simultaneously. The increment of the ion beam energy during the deposition process led to decreasing of metal Cr grain size and the rapid change of resistivity above the critical $O_2$ partial pressure.