• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.299-302
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• 2005

Semisolid A356 slurries were prepared by electromagnetic stirring casting and by inoculation of Al-5Ti-B master alloy. As stirring time and addition of Al-5Ti-B are different, the grain size of the primary phase is different. Through the experiment of rheocast in a Buhler horizontal die casting machine, it was found that the finer the equiaxed primary dendrites, the smoother the die filling and better cast quality. Small equiaxed primary dendrite also results in less liquid segregation on the surface.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.408-410
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• 2008

The evolution of texture and microstructure during recrystallization was tracked after different cold rolling of aluminum sheets. Texture of the sheet center were differentiated by different strain states due to prior deformation. The evolution of recrystallization texture was studied with the amount of shear applied during cold rolling. The final grain size after recrystallization annealing was varied due to the effective strain during deformation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.528-530
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• 2008

The effect of consolidation temperature on the microstructure, density and mechanical properties (especially, wear property) of $Al_{92.5}-Fe_{2.5}-Cr_{2.5}-Ti_{2.5}$ alloy fabricated by gas atomization and magnetic pulsed compaction was investigated. All consolidated alloys consisted of homogeneously distributed fine-grained fcc-Al matrix and intermetallic compounds. Relative higher mechanical properties in the MPCed specimen were attributed to the retention of the nanostructure in consolidated bulk without cracks. The as consolidated bulk by magnetic pulsed compaction showed the enhanced wear properties than that of a general consolidation process. In addition, the wear mechanism and fracture mode of MPCed bulk was discussed.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1378-1389
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• 2005

This work provides the fundamental knowledge of energy transport characteristics during very short-pulse laser heating of semiconductors from a microscopic viewpoint. Based on the self-consistent hydrodynamic equations, in-situ interactions between carriers, optical phonons, and acoustic phonons are simulated to figure out energy transport mechanism during ultrafast pulse laser heating of a silicon substrate through the detailed information on the time and spatial evolutions of each temperature for carriers, longitudinal optical (LO) phonons, acoustic phonons. It is found that nonequilibrium between LO phonons and acoustic phonons should be considered for ultrafast pulse laser heating problem, two-peak structures become apparently present for the subpicosecond pulses because of the Auger heating. A substantial increase in carrier temperature is observed for lasers with a few picosecond pulse duration, whereas the temperature rise of acoustic and phonon temperatures is relatively small with decreasing laser pulse widths. A slight lagging behavior is observed due to the differences in relaxation times and heat capacities between two different phonons. Moreover, the laser fluence has a significant effect on the decaying rate of the Auger recombination.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.1
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• pp.84-88
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• 1995

Various heat-treatments were conducted to Ti-48.1at%Al and Ti-48.3at%Al-1.2at%Mn alloys casted by plasma arc melting system. Mechanical properties, microstructure and high temperature oxidizing behaviors of as-casted and heat-treatment alloys were investigated. Ti-48.1Al and Ti-48.3Al-1.2Mn alloys were decreased in strength according to increased of heattreatment temperature. Oxidizing weight gain of Ti-48.1Al alloy which conducted at $1273^{\circ}K$ was linearly increased. In case of adding Mn to alloy, there was no rapid increase of oxidizing weight gain during early time.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.4
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• pp.189-198
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• 2008

The production of automotive chassis parts requiring both high hardness and good shape-holdability is better realized by using press quenching technology, comprising the austenitizaton and the subsequent press quenching in a specially designed stamping tool. The effect of press quenching mold shape on the hardness distribution, bending height, and degree of planeness of automotive flexible plate during press quenching and tempering has been investigated. The preferable shape of the projections of punch and die in contact with the flexible plate was close to oval to improve the flow of cooling oil, leading to the higher hardness. The press quenching mold with three separate parts was more effective to control the dimensional change due to thermal deformation during press quenching. Some decrease in the bending height during tempering may be related to some recovery of the residual stress at $400^{\circ}C$.

• Journal of Surface Science and Engineering
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• v.34 no.4
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• pp.303-312
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• 2001

Composition and microstructure of the tin-zinc alloys electroplated in gluconate bath were studied according to pulse current parameters. The cathode current efficiency increased with both the mean current density and the off-time decrease. Zinc content of the alloy deposits increased with increasing mean current density, while it decreased noticebly with increasing the off-time from 10-30ms to 100-150ms. The preferred orientation of the alloy deposits changed with the increase of peak current density in the sequence of (220)longrightarrow(220)+(420) or (220)+(420)+(321) mixed structure. The equiaxed grain size of the alloy increased with the increase of off-time and the decrease of mean current density.

• Journal of Surface Science and Engineering
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• v.25 no.3
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• pp.133-143
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• 1992

Titanium nitride(TiN) films have been prepared by HCD plasma enhanced reactive ion plating. Density and temperature of the plasma generated by the HCD were investigated. It was shown that parameters such as the substrate bias voltage(0 350V) and N2 flow rate(10 180SCCM) influenced the growth, the growth, the microstructure and the color tone of the film mostly. In order to study the interface region, surface analysis by AES combined with sputter depth profiling was performed. Microhardness of the coated TiN films were measured by micro Vickers hardness tester. Also, the effect of coating parameters on composition, coating surface and fracture morphology, grain size and growth rate were examined.

• Journal of Surface Science and Engineering
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• v.27 no.5
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• pp.285-291
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• 1994

The effects of pulse current parameters on the composition and the microstructure of Pd-Ni alloy electrodeposits were studied. The cathode current efficiency of p.c. electrolysis conditions decreased with increasing both mean and peak current density and was lower than those under D.C. electrolysis condition. Palladium content of Pd-Ni alloy increased with increasing both peak current density and on-time, while it decreased with increasing mean current density and duty cycle. The preferred orientation of Pd-Ni alloys changed with increasing mean current density in the sequence of (111)+(110).(100) or (110)longrightarrow(111)longrightarrow(100) or random distribution of crystal structure. The surface morphology of Pd-Ni alloy changed mainly according to the mean current density and was related to the preferred orientation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.295-295
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• 2012

The $TiO_2$ films were prepared in the $H_2SO_4$ solution containing $NH_4F$ at different anodic voltages, to compare the photocatalytic performances of titania for purification of waste water. The microstructure was characterized by a Field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD). Chemical bonding states and co-doped elements of F and N were analyzed using surface X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the co-doped $TiO_2$ films was analyzed by the degradation of aniline blue solution. From the result of diffuse reflectance absorption spectroscopy(DRS), it is indicated that the absorption edge of the F-N-codoped $TiO_2$ films shifted toward visible light area, and the photocatalytic reaction of $TiO_2$ was improved by doping an appropriate contents of F and N.