• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.38-40
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• 1988

This paper was a study on dielectic characteristics of polypropylen film which were annealled in air and qunched in nitorgen after aging for 5[Hr]. Dielectric characteristics of specimen were measured in temperature of the range of 15-120[$^{\circ}C$], and in frequency of the range of $30-1{\times}10^6$[Hz.] As the result, for dielectric relaxation $\beta$-peak was observed in 20[$^{\circ}C$], and $\alpha$-peak was observed in 90[$^{\circ}C$]. Also, it was explained that $\alpha$-peak attributed due to armorphous region and $\beta$-peak attributed due to crystalline region and activation energy from dielectric loss spectra was obtained 34.5[kcal/mole] for $\alpha$-peak and 80.5[Kcal/mole] for $\beta$-peak, respectively.

• Polymer(Korea)
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• v.27 no.3
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• pp.249-254
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• 2003

The variation of chemical structure and physical properties of crosslinked polyethylene (XLPE) during thermal aging process was investigated. The formation of carbonyl functional group resulting from thermal oxidation reaction of XLPE was monitored using X-ray photoelectron spectroscopy and near infrared (NIR) spectroscopy. It was observed that the intensity of carbonyl peak observed at 1715 nm linearly increased with aging time in NIR spectroscopy. The linear relationship between NIR peak absorbance and aging time confirmed that NIR spectroscopy might be used as a proper tool for monitoring the aging process of polymeric materials. Also the formation of crosslinks during the aging process was monitored using thermal mechanical analysis, stress-strain test, and Shore hardness test. The change in the physical properties, such as the increase in the glass transition temperature from 110 to 132$^{\circ}C$, the decrease in the strain from 265 to 110%, as well as the increase in the shore D hardness from 32 to 50, was observed during the aging process.

• Journal of Welding and Joining
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• v.19 no.2
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• pp.176-181
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• 2001

Reflow soldering characteristics of Sn-3.5Ag and Sn-37Pb balls for BGA(Ball grid Array) were investigated. Diameter of 0.76mm ball was set on a Cu/Ni/Au-coated pad and reflowed in air with changing peak soldering temperature and conveyor speed. Peak temperatures were changed from 240 to 28$0^{\circ}C$ for Sn-3.5Ag, and from 220 to 26$0^{\circ}C$ for Sn-37Pb balls. As results, heights of solder balls increased and widths decreased with peak soldering temperature. Through aging treatment at 10$0^{\circ}C$ for 1.000 hrs, average hardness of Sn-3.5Ag balls bonded at 25$0^{\circ}C$ cecreased from 14.90Hv to 12.83Hv And with same aging conditions, average shear strength of Sn-3.5Ag balls bonded at 26$0^{\circ}C$ decreased from 1727gf to 1650gf.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.322-325
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• 2007

Precipitation characteristics of the Fe-36Ni based high strength Invar alloy for power transmission wire was investigated in this study. High strength can be obtained in this alloy through solution hardening, precipitation hardening and strain hardening by cold working. In the present study, ingots of Fe-36Ni based Invar alloys with the contents of C, Mo and V varied. Microstructure observations by OM, SEM, and TEM were carried out to validate the simulation results. BCC phase and $FeNi_3$ phase are also expected at lower temperatures below $500^{\circ}C$. Aging treatments were carried out at temperatures ranging from 400 to $900^{\circ}C$ for time intervals from 3 min to 100hrs. Peak aging condition was obtained as $400^{\circ}C$ and 1 hr. With temperature increased, peak strength was decreased abruptly. Microstructure observation was conducted by optical microscopy, scanning electron microscopy, and transmission electron microscopy.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.255-265
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• 1997

Precipitation and strengthening mechanisms in squeeze cast Mg-8.5wt%Li-4.5wt%Al have been investigated by differential scanning calorimetry(DSC), scanning electron microscopy(SEM), in-situ and ex-situ X-ray diffraction analysis and hardness measurement. Special emphasis was placed on the investigation of the precipitation behavior by the DSC technique. Microstructural and calorimetric analysis showed that ${\theta}$ and ${\delta}$ precipitates in the b.c.c. ${\beta}$ phase matrix, forming two exothermic peaks at the temperature ranges of $130^{\circ}C{\sim}180^{\circ}C$ and $236^{\circ}C{\sim}280^{\circ}C$. ${\theta}$ and ${\delta}$ dissolve into the matrix forming an endothermic peak at the temperature range of $280^{\circ}C{\sim}352^{\circ}C$. The as-cast microstructure consists of ${\alpha}$, ${\beta}$ and ${\delta}$. Peak strength was obtained after aging for 1 hour at $50^{\circ}C$. The aging time required for the peak strength decreased as the aging temperature increases. The hardness decrease during overaging was due to the coarsening of ${\theta}$ precipitates. Microhardness measurement showed that variation of the hardness of ${\beta}$ matrix was more pronounced than that of the ${\alpha}$ phase, indicating that the ${\beta}$ phase is more responsible for the strengthening of the Mg-8.5wt%Li-4.5wt%Al alloy.

• Electrical & Electronic Materials
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• v.1 no.1
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• pp.54-61
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• 1988

This paper was a study on dielectric phenomena of the specimen, Polypropylene films which were annealled in air and quenched in liquid nitrogen after aging for 5[hr] in water of 100[.deg.C]. The specimen was measured in temperature range of 15-120[.deg.C] and in frequency range of 30-1x 10$^{6}$ [HZ]. As the results of the study, it was confirmed that the tacticity of specimen was isotactic structure, and the degree of cryatallinity of the specimens calculated by means of Natta's method from XRD (X-ray Diffraction) spectrum was 55[%]. And for dielectric relaxation, .betha. peak-the tan .delta. (spectrum around 20[.deg.C])-attributed due to amorphous regions, and .alpha. peak - the tan .delta. spectrum around 90[.deg.C]-due to crystalline regions. It was identified that the degree of crystallinity of the specimen quenched in the liquid nitrogen was increased to 55-65[%], and that of the specimen annealled in the air was decreased to 55-50[%]. And activation energy from dielectric loss spectra was obtained 34.5[kcal/mole] for .alpha. peak and 80.5[kcal/mole] for .betha. peak, respectively.

• Journal of Korea Foundry Society
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• v.20 no.5
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• pp.300-306
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• 2000

The objective of this work was to investigate the effects of SiC particle size(50, 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on aging behavior in Al-5Mg-X(Si,Cu,Ti)/SiCp composites fabricated by pressureless infiltration method using hardness and wear test, scanning electron microscopy(SEM) and differential scanning calorimetry(DSC). The peak aging time in Al-5Mg-X(Si, Cu, Ti)/SiCp(50, 100 ${\mu}m$) composites is shorter than Al-5Mg-0.3Si alloy.The peak aging time of 50 ${\mu}m$ SiC particle reinforced Al-5Mg-X(Si,Cu,Ti) composites is shorter than those of 100 ${\mu}m$ SiC particle reinforced of Al-5Mg-X(Si,Cu,Ti) composites. The Al-5Mg-0.3Si-0.1Cu-0.1Ti/SiCp(50 ${\mu}m$) composites aged at $180^{\circ}C$ has higher hardness and better wear resistance than any other aged composite.The aging effect is promoted by the addition of Si and Cu in Al-5Mg/SiCp composites, so the wear resistance of Al-5Mg/SiCp composites with Si and Cu elements is enhanced by the aging treatment.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.6
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• pp.306-310
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• 2007

Changes in microstructure and damping capacity with aging time for solutionized Mg-Al alloy have been investigated. Discontinuous ${\beta}\;(Mg_{17}Al_{12})$ precipitates form along the primary grain boundaries, the amount of which increases as the aging time increases. The hardness of the matrix with respect to aging time shows a typical "S" shape, indicating a generation of fine continuous precipitates in the matrix during the aging. The peak level of damping capacity is obtained after 1 hour of aging, over which the damping capacity becomes deteriorated continuously. The formation of optimum density of continuous ${\beta}$ precipitates with fine morphology which would act as pinning points for dislocation lines, might be responsible for the improvement of damping capacity.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.172-177
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• 2006

Aging characteristics and mechanical properties of commercial 7xxx series Al composites were investigated from viewpoint of ceramic contents. After sintering process, sintered densities of blended and composite powder were 95 and 97%, respectively. Each part was solution-treated at $475^{\circ}C$ for 60 min and aged $175^{\circ}C$. And two-step aging was also performed form $120^{\circ}C$ to $175^{\circ}C$. The aging behavior of the sintered composite pow-der was different from that of sintered blended powder. The peak aging time of the composite was rapid as well due to strain. Before aging, mechanical properties of sintered composite powder was significantly higher than that of sintered blended powder. These increments of properties were directly affected by ceramic particles. However, after aging, incremental rate of mechanical properties was slowed in the composite.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.1
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• pp.30-36
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• 1991

Effects of aging treatment on the mechanical properties of a 18 Ni maraging steel were investigated by considering the reverted austenite. Specimens were heat treated by austenitizing at $840^{\circ}C$ for 1 hr and then aged for various times at $480^{\circ}C$ and $520^{\circ}C$. The main results obtained are as follows : 1) The amounts of reverted austenite are increased up to about 4% at $480^{\circ}C$ and about 22% at $520^{\circ}C$ with 1 to 48 hrs aging time. 2) Decreasing tendencies of impact energy and fracture toughness with increasing aging time are diminished after aging for 2 hrs at two aging temperatures of $480^{\circ}C$ and $520^{\circ}C$. 3) Peak hardness and yield strength are obtained after aging for 4 hrs at $480^{\circ}C$ and 2 hrs at $520^{\circ}C$ respectively. From the above results, it was concluded that the optimum aging condition with which showed good strength and toughness combination are given to be $480^{\circ}C$ for 4 hrs and $520^{\circ}C$ for 2 hrs.