• Transactions of Materials Processing
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• v.22 no.8
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• pp.450-455
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• 2013

In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.

• Journal of the Optical Society of Korea
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• v.9 no.2
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• pp.74-78
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• 2005

With the fast Q-tensor method, which can model the defect dynamics in a liquid crystal director field, the nucleation and dynamical behavior of defects is modeled. In order to model the defect, hormeotropic aligned liquid crystal cell with step inhomogeneous electrode which has a height of $1\;{\mu}m$ is used. From the simulation, we can observe the nucleation and line of the defect from surface inhomogeneity and the experiment is performed for confirmation. The experimental result is compared with numerical modeling in order to verify the simulation of the defect nucleation.

• Tribology and Lubricants
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• v.11 no.5
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• pp.20-25
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• 1995

Diamond films were prepared by a hot filament vapor deposition onto polycrystal silicon nitride substrates. Different kinds of silicon nitride containing CaO and $Fe_{2}O_{3}$ were manufactured to investigate the impurity effect of substrate on the morphology of diamond films and their wear behaviors. Nucleation rates and morphologies of diamond films deposited on various kinds of silicon nitride were compared. The highest nucleation rate was observed in a substrate containing 1% of CaO. Wear tests were performed with a silicon nitride ball on the disk geometry to investigate the tribological behavior of diamond film against silicon nitride. This study demonstrated that different morphologies of diamond film due to substrate impurities produced different wear behavior against silicon nitride.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.80-85
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• 2011

The crystallization behavior and microstructural change of the glass-ceramics were analyzed as a function of concentration and etching time of the HF solution in order to enhance the degree of crystallinity induced by heterogeneous nucleation of glass of bottom ash containing 15 wt% $Li_2O$. The nucleation site seemed to be generated where the Si ion was eluted. The main crystal phases in the glass-ceramics fabricated in this study were $\beta$-spodumene and $Li_2SiO_3$. The specimens etched with HF of 0.5 vol% within 0~60 seconds showed increased crystalline peak intensities in XRD pattern with etching time compared to no-etched one. Also the crystal size and crystal occupancy in the glass matrix observed by SEM were increased with etching time. For the glass-ceramics etched with 1.0 and 2.0 vol% HF solution, the etching time over 10 s was not effective to increase the crystallinity. From this study, it was found that the glass-ceramics with the higher crystallinity could be obtained by HF-etching followed by heat treatment process, even though the nucleating agent or 2-stages thermal treatment process were not used.

• Journal of Magnetics
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• v.8 no.3
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• pp.108-112
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• 2003

We report the experimental finding that there exists a transition of magnetization reversal process with varying the applied field in Co/Pd multilayer. We have measured the wall-motion speed V and the nucleation rate R during magnetization reversal via time-resolved direct domain observation, where the magnetization reversal process of Co/Pd multilayer is found to take a transition from thermal activation process to viscous process at the critical field of about 1.87 H$\_$C/ (coercivity). In the thermal activation regime, we find that the field dependences of two activation volumes for the wall-motion process and the nucleation process are different with each other, which reveals that the wall-motion and nucleation experience completely different interactions. In the viscous regime, we find that the wall-mobility is much smaller than a typical value for the sandwiched Co films, which implies that the Co/Pd interfaces in multilayer substantially contribute to the dynamic dissipation.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.19-22
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• 2015

The joining behavior of YSZ ceramics to the glasses used in the $9Al_2O_3-24ZrO_2-51SiO_2-16R_2O$ and $9Al_2O_3-24ZrO_2-51SiO_2-7La_2O_3-9R_2O$ (wt%) glass systems was investigated. The glass transition and softening temperatures were determined to be $430^{\circ}C$ and $760^{\circ}C$, respectively. The behavior of the contact angle was inversely proportional to an increase in the temperature. The Zr element in YSZ acted as a nucleation agent and contributed to the bonding behavior at the interface.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.7
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• pp.759-766
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• 1988

the effect of heat treatment in oxygen ambient on the nucleation and growth of oxidation induced stacking faults(OSF) in n-type(100)silicon wafer has been investigated. The growth of OSF is determind as a function of oxygen concentration in silicon wafer, heat treatment time and temperature, and the activation energy for the growth of OSF can be obtained from the growth kinetics. The activation energies are respectively 2.66 eV for dry oxidation and 2.37 eV for wet oxidation. In this paper, we have also studied the structural feature of OSF with the comparison of optical microscopic morphology and crystalline structure.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.279-286
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• 2000

Magnetic field dependence of magnetization reversal in Co/Pt multilayers has been quantitatively investigated. Serial samples of Co/Pt multilayers have been prepared by dc-magnetron sputtering under various Ar pressure. Magnetization reversal was monitored by magnetization viscosity measurement and direct domain observation using a magneto-optical microscope system, and the wall-motion speed and the nucleation rate R were determined using a domain reversal model based on time-resolved domain reversal patterns. Both and R were found to be exponentially dependent on the reversing applied field. From the exponential dependencies, the activation volumes of the wall motion and nucleation could be determined based on a thermally activated relaxation model, and the wall-motion activation volume was revealed to be slightly larger than the nucleation activation volume.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.472-480
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• 2000

A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion was obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stresses for a spherical thick-walled shell and by fitting the finite element results of a voided cube. The macroscopic yield criterion is valid for negative mean normal stresses as well as for positive mean normal stresses. From the yield criterion, a plastic potential function for the porous solids was derived either for plastic normality flow or for plastic non-normality flow of pressure- sensitive matrices. In addition, the elastic relation, an evolution equation of the plastic flow stress of the matrices and an evolution equation of the void volume fraction were presented to complete a set of constitutive relations. The set of constitutive relations was implemented into a finite element code ABAQUS to analyze the material behavior of rubber-toughened epoxies. The cavitation and the deformation behavior were analyzed around a crack tip under three-point bending and around notch tips under four-point bending. In the numerical analyses, the cavitation of rubber particles was considered via a stress-controlled nucleation model. The numerical results indicate that a reasonable cavitation zone can be obtained with void nucleation controlled by the macroscopic mean normal stress, and a plastic zone is smaller around a notch tip under compression than under tension. These numerical results agree well with corresponding experimental results on the cavitation and plastic zones.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.51-59
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• 1991

Early stage of GaAs nucleation on Si substrate was theoretically studied by computer simulation. Compared to the constant ledge interaction energy in conventional nucleation theory, functional behavior of ledge-ledge interaction resulted in small size clusters depending on the cluster size and shape. Among various kinds of clusters, the multilayer pyramidal shape GaAs cluster requires smallest excess free energy due to the formation of Ga(111) facet planes. There this result suggests that the defects involved in GaAs/Si are originated from the early stage nucleation.