• Corrosion Science and Technology
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• v.6 no.3
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• pp.96-102
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• 2007

The resistance of the linepipe steel to hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) is very important for steel to be used in sour oil/gas environments. Welding of steels is necessary to the construction of pipe-line transporting oil/gas. In this study, HIC and SSC resistance of an electric resistance welded (ERW) steel plate which belongs to API X70 grade was evaluated by using NACE TM0284-96A and NACE TM0177-96A methods. HIC and SSC fracturing behavior was investigated by observing fractured surfaces using optical microscopy (OM) and scanning electron microscopy (SEM). It was discussed in terms of metallurgical parameters such as the distribution of primary microstructure, second phases and inclusions. Results showed that the weld joint of ERW steel is more sensitive than base metal to HIC and SSC. This is due to difference in the contribution of metallurgical parameters to HIC and SSC nucleation and propagation.

• Journal of Korea Foundry Society
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• v.18 no.3
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• pp.234-239
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• 1998

Unidirectional solidification of $Al-CuAl_2$ eutectic composites was studied under the condition of forced convection by vibration. It has been shown that thermal gradient for solid is different from that for liquid during solidification under force convection by vibration. With increase of vibration, mobility of liquid increases, but decreases with decreasing vibration. The rate of solidification is very high initially, and decreases suddenly. For further solidification, the rate of solidification decrceases slowly, and shows a L-type behavior. The mechanical vibration during solidification effects efficiently on nucleation, and induces a forced convection in liquid. By the forced convection, great thermal gradient of liquid interface between solid and liquid can be obtained. The amount of solute near the interface also decreases as solute distribution is improved by the forced convection.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.7
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• pp.767-773
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• 1988

We have proposed a new simple and easy method for the observation of OSF growth and shrinkage. This method is to observe the behavior of OSF in thedamaged region during oxidation as well as annealing process after introducing mechanical damage on the silicon surface by pressure-controllable indentor. The effect of SiO2 layer on the shrinkage of pregrown OSF generated by the proposed method has been investigated using the samples with or without SiO2 layer. From the experimental data, we suggest a model for the shrinkage of OSF, which is based on the recombinaiton mechanism between silicon interstitial and vacancy at the Si-SiO2 interface.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.21-38
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• 2009

The use of multi scale modeling concepts and simulation techniques to study the destabilization of an ultrathin layer of oxide interface between a metal substrate and the surrounding environment is considered. Of particular interest are chemo-mechanical behavior of this interface in the context of a molecular-level description of stress corrosion cracking. Motivated by our previous molecular dynamics simulations of unit processes in materials strength and toughness, we examine the challenges of dealing with chemical reactivity on an equal footing with mechanical deformation, (a) understanding electron transfer processes using first-principles methods, (b) modeling cation transport and associated charged defect migration kinetics, and (c) simulation of pit nucleation and intergranular deformation to initiate the breakdown of the oxide interlayer. These problems illustrate a level of multi-scale complexity that would be practically impossible to attack by other means; they also point to a perspective framework that could guide future research in the broad computational science community.

• Korean Journal of Materials Research
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• v.17 no.7
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• pp.371-375
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• 2007

In-situ observation of electromigration behavior of eutectic SnPb solder was performed as a function of line length at $100^{\circ}C$, $6{\times}10^4A/cm$ condition in a scanning electron microscope chamber. The incubation time for edge drift and the edge drift velocity increase as line length increases, which are discussed with the void nucleation stage of solder bump and the electromigration back flux force, respectively. Finally, the existence of electromigration product (jL) and its line length dependency are also discussed.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.694-696
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• 2002

Growth behaviors of carbon nanotubes (CNTs) are studied in terms of catalyst by using scanning electron microscopy and transmission electron microscope (TEM). Catalyst films deposited on various substrates are agglomerated into nano-islands during the heat-up to the growth temperature. In particular, we focus on the direct investigation of the microstructures of the CNTs and the interface of CNTs-catalyst-substrate using cross-sectional TEM. We investigate relationship to the subsequent CNTs growth on each nucleation site. The growth of CNTs depends on the catalyst itself but not the silicide formation between the catalyst and the substrate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.84-89
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• 1996

The nucleation and growth of microporosities was observed during the course of annealing treatment of sputter-deposited AgInSbTe thin films. There was a close correlation between the density of microporosity and the sputtering gas pressure in annealed thin films. The void density for a given composition decreased with sputtering gas pressure. It was shown from the present study that the number of porosities decreased while the average porosity size increased as the annealing temperature and holding time increased. The mechanism of porosity formation in the sputter-deposited AgInSbTe thin flus containing Ar-impurity trapped from the Ar-plasma is discussed in the present article.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.456-459
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• 2005

Continuous cooling transformation behaviors were studied fur low carbon HSLA steels containing three different level $(1\~3\;wt\%)$ of Ni addition. Thermo-mechanical processing (TMP) simulations to construct continuous cooling (CCT) diagram were conducted by using Gleeble system. As cooling rate increased, pearlite, granular bainite, acicular ferrite, bainitic ferrite and lath martensite were transformed from deformed austenite. Fully bainitic microstructure were developed at all cooling rate condition in high Ni containing steel due to hardenability increasing effects of Ni. Ni also influenced the transformation kinetics. At the slowest cooling rate of $0.3^{\circ}C/s$, transformation delayed with decreasing Ni contents because of the diffusion of substitutional alloy elements. However, cooling rate slightly increased to $1^{\circ}C/s$, transformation kinetics accelerated with decreasing Ni contents because nucleation of bainite was sluggish due to hardening of residual austenite.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.389-396
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• 1993

We studied the crystallization behavior of amorphous PbTiO3 thin film grown at 30$0^{\circ}C$ by RF magnetron sputtering on Pt substrate. Crystallization to full perovskite phase was observed after annealing at 475$^{\circ}C$, for 9min, without PbO volatilization. The higher the annealing temperature, the shorter the time required for crystallization. The isothermal kinetic study at 475$^{\circ}C$ showed that the Avrami constant was approximately 4, which implies that the crystallization can be characterized by isotropic 3-dimensional growth with a constant nucleation rate. The TEM study revealed that the crystallized thin film was composed of very fine (20~100nm) grains oriented randomly without any evidence of 90$^{\circ}$domain boundaries.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.230-234
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• 2006

Metal-Induced Crystallization (MIC) of amorphous silicon (a-Si) using aluminum and nickel as catalysts were performed with a variation of metal thickness and temperature. Raman results showed that the crystallization of a-Si depended on the thickness of aluminum while not on nickel. Nickel that forms silicide nodules during annealing simply catalyzed the formation of crystalline silicon (c-Si) while aluminum was consumed and transferred during MIC, which resulted in more complex microstructural characteristics. Crystalline silicons after NIC had elongated shape with a twin along the long axis. Morphological change after Aluminum-Induced Crystallization (AIC) showed more equiaxial grains. The nucleation and growth mechanism of AIC was discussed.