• Bulletin of the Korean Chemical Society
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• v.14 no.2
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• pp.297-299
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• 1993

• Journal of the Korean Society for Heat Treatment
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• v.18 no.5
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• pp.305-311
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• 2005

Effect of Cr contents(Cr: 0.27, 0.45 and 0.65wt.%) on precipitation process has been studied by electrical resistivity measurements, hardness and scanning electron microscope. The first stage of the process consists of the formation of Cr-rich particles, the second stage consists of the competitive growth of these particles. The kinetics of precipitation could be described by Johnson-Mehl-Avrami equation, $f(t)=1-\exp(-kt^n)$. The values of n were found to be in the range from 0.17 to 0.39 at the first stage and from 1.0 to 1.5 at the second stage. The activation energies of Cu-Cr alloys were determined by Cross-Cut method and were 90~136 kJ/mol. The maximum hardness value of $H_RB$ 84 was obtained in Cu-0.65wt.%Cr alloy.

• Journal of Korea Foundry Society
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• v.28 no.1
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• pp.31-36
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• 2008

Ti-Ni-Cu alloys are very attractive shape memory alloys for applications as actuators because of a large transformation elongation and a small transformation hysteresis. Rapidly solidified Ti-Ni alloy ribbons have been known to have the shape memory effect and superelasticity superior to the alloy ingots fabricated by conventional casting. In this study, solidification structures and shape memory characteristics of $Ti-Ni_{30}-Cu_{20}$ alloy ribbons prepared by melt spinning were investigated by means of DSC and XRD. Operating parameters to fabricate the amorphous ribbons were the wheel velocity of 55 m/s and the melt spinning temperature of $1500^{\circ}C$. The crystallization temperature was measured to be $440^{\circ}C$. The crystallized ribbons exhibited very fine microstructure after annealing at $440^{\circ}C$ for 10 minutes and $460^{\circ}C$ for 5 minutes and was deformed up to about 6.8% and 6.23% in ductile manner, respectively. Stress-strain curve of the ribbon exhibited a flat stress-plateau at 64 MPa and this is associated with the stress-induced a B2-B19 martensitic transformation. During cycle deformation with the applied stress of 220 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be $4.3^{\circ}C$ and 3.6%.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.3
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• pp.1-6
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• 1991

In this study, intermediate thermo-mechanical treated Al-2.0 wt%Li, and Al-2.0 wt%Li-1.2 wt%Cu-1.0 wt%Mg-0.12 wt%Zr alloys were tested in tension at $10^{\circ}C$ and elevated temperature(100, 200 and $300^{\circ}C$). The results are follows : The tensile strength of Al-Li-Cu-Mg-Zr alloy is the highest but the elongation of Al-Li alloy is the highest(106%) among the all alloys in tension at $300^{\circ}C$. The Portervin-LeChartlier effect is showed in AI-Li-Cu-Mg-Zr alloy at 10 and $100^{\circ}C$, because of tangled dislocation by Mg and Cu. In the true stress-strain curves of all alloy, the peaks of stress at $300^{\circ}C$ are showed at the strain less than 0.1. In the binary alloy, the dynamic restoration process at 200 and $300^{\circ}C$ is nearly similar to dynamic recovery type. The hot deformation stress is decreased with increase of dynamic recovery degree, but the elongation is increased. When the strain the strain rate are constant, the temperature dependence of hot deformation stress is increased with increase of deformation temperature. The elongation and degree of dynamic recovery are decreased with increase of hot deformation activation energy, but the deformation stresses slightly increased.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.542-549
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• 2020

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al₃Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al₃Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al₃Sc precipitates and dense Al₂Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al₃Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.216-221
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• 1992

Annealing effects on the permeability aftereffect(disaccommodation) of liquid quenched single strip $Fe_{73.5}Cu_1Nb_3Si_{16}B_{6.5}$ alloys were investigated with pulse method. The initial susceptibility X, $B_{10},$ (the flux density at 10 Oe) and disaccommodation intensity D (D = [X(1 s)-X(64 s)]/X(1 s), where X(1 s) and X(64 s) are the susceptibility of 1 and 64 s of rest time after A. C. demagnetization) were about 800, 0.8 T and 16 %, respectively. The soft magnetic properties were improved with isothermal annealing for 1 hour at $300{\sim}600^{\circ}C.$ X, $B_{10},$ and D at $570^{\circ}C$ of optimum annealing temperature were 15000, 1.2 T and 1.1 %, respectively. The origin of the change of characteristics were examined with fine crystalline structure and magnetostriction.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.132-139
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• 1995

Tnermomechanical treatment consisting of homogenizing, hot and warm rolling were introduced to Al-MgCu-Mn alloys for obtaining superplasticity. The factors affecting the superplasticity of the alloys were investigated by optical and transmission electron microscopy. Large particles which had not been decomposed during homogenizing treatments remained stable in the hot and warm rolling processes. These particles were a source of cavitation and poor elongation in superplastic deformation. On the other hand, fine precipitates were produced during thermomechanical processing, and resulted in improvement of superplasticity by stabilizing microstructure. Two-step homogenizing and air cooling process was more effective than onestep homogenizing and furance cooling process in removing microsegregations and producing fine particles.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.672-677
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• 1998

The following work examines the growth rate and microstructure of the $AI_2O_3$-composite formation by melt oxdation of pentad AI-alloys. The I weight % of each metal elements Cu and Ni were added to AI-IMg-3Si-3Zn and AI-IMg- 3Si-5Zn alloys. The diffenent pentad AI-alloys were oxidized 20 hours long at 1373K and 1473K. The oxidation rates were determined by observing the weight gain. The macro- and microstructure of formed oxide layer were examined by optical microscopy. The AI-IMg-3Si-5Zn-lCu alloy revealed the best oxidation behavior, but formedoxide layer was inhomogeneous.The oxidation rate were accelerated, and the uniform growth of the oxide layer with fine microstructure were obtained by putting a thin layer of $SiO_2$ on the surface of the alloy.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.91-97
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• 2014

With Pb-free solder joints containing Sn-Ag-Cu-based ternary alloys (Sn-1.0 wt.%Ag-0.5Cu and Sn-4.0Ag-0.5Cu) and Sn-Ag-Cu-In-based quaternary alloys (Sn-1.0Ag-0.5Cu-1.0In, Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.6In, and Sn-1.2Ag-0.7Cu-0.4In), fracture-mode change, shear strengths, and fracture energies were observed and measured under a high-speed shear test of 500 mm/s. The samples in each composition were prepared with as-reflowed ones or solid-aged ones at $125^{\circ}C$ to 500 h. As a result, it was observed that ductile or quasi-ductile fracture modes occurs in the most of Sn-Ag-Cu-In samples. The happening frequency of a quasi-ductile fracture mode showed that the Sn-Ag-Cu-In joints possessed ductile fracture properties more than that of Sn-3.0Ag-0.5Cu in the high-speed shear condition. Moreover, the Sn-Ag-Cu-In joints presented averagely fracture energies similar to those of Sn-Ag-Cu joints. While maximum values in the fracture energies were measured after the solid aging for 100 h, clear decreases in the fracture energies were observed after the solid aging for 500 h. This result indicated that reliability degradation of the Sn-Ag-Cu-In solder joints might accelerate from about that time.

• Journal of Powder Materials
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• v.4 no.2
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• pp.122-132
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• 1997

Nanostructured(NS) W-Cu composite powders of about 20~30 nm grain size were synthesized by mechanical alloying. The properties of NS W-Cu powder and its sintering behavior were investigated. It was shown from X-ray diffraction and TEM analysis that the supersaturated solid solution of Cu in W was not formed by the mechanical alloying of mixed elemental powders, but the mixture of W and Cu particles with nanosize grains, i.e., the nanocomposite powder was attained. Nanocomposite W-20wt%Cu and W-30wt%Cu powders milled for 100 h were sintered to the relative density more than 96% and 98%, respectively, by sintering at 110$0^{\circ}C$ for 1 h in $H_2$. Such a high sinterability was attributed to the high homogeneous mixing and ultra-fine structure of W and Cu phases as well as activated sintering effect by impurity metal introduced during milling.