• Journal of the Korean Society for Heat Treatment
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• v.13 no.1
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• pp.1-9
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• 2000

The microstructural characteristics and low temperature tensile properties between $25^{\circ}C$ and $-196^{\circ}C$ for as-welded and age hardened specimen by using Al 5083-H321 for base metal, 5083-5356 and 5083-4043 weldments have been investigated. The hardness of 5083-5356 weldment decreases with aging treatment, whereas the weld region of 5083-4043 weldment shows remarkable increase in hardness after aging due to the precipitation of fine Si particle at the grain boundaries and interiors. Low temperature tensile properties of 5083 AI base metal, 5083-5356 and 5083-4043 weldments appear to be the increment of tensile strengths and elongations at the room temperature and $-196^{\circ}C$, while the decrement of tensile properties around $-50^{\circ}C$ is shown. Through the observation of fine serration to fracture in the stress-strain curve and tensile fractography, the increment of localized deformation leading to promote the neck initiation and the increment of the dimple size cause to decrease in tensile strengths and elongations around $-50^{\circ}C$. For the tensile specimen of the 5083 base metal, 5083-5356 and 5083-4043 weldments, the reason to increase in elongation after solution and aging treatment is the diminishment of fine pit, the resolution of Mg into the matrix and the spheridization of the eutectic Si.

• Journal of Trauma and Injury
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• v.20 no.2
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• pp.115-118
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• 2007

Purpose: A eutectic mixture of local anesthetics (EMLA$^{(R)}$) cream has been used as a topical anesthetic to reduce the pain of procedures penetrating the skin. It is generally applied for 40 to 60 minutes before the painful procedure. Because of the long application period, EMLA$^{(R)}$ is not useful in the emergency department (ED). The purpose of this study was to determine whether a 20-minute application of 9.6% lidocaine would be useful in reducing the pain of routine peripheral intravenous cannulation in the ED. Methods: We examined 27 male and 19 female patients ages over 18 years of age who required intravenous cannula insertion. Intravenous insertion was performed on 46 patients: 24 patients in the placebo group (mean age: 40.0 years) and 22 in the 9.6% lidocaine group (mean age: 37.6 years). The 9.6% lidocaine or placebo gel was applied and covered with an occlusive dressing for 20 minutes. Pain was scored by the patients using a 0- to 10-cm visual analogue scale. Results: The patients in the 9.6% lidocaine group (mean pain score: 3.4) experienced less pain than those in the placebo group (mean: 5.3), and the difference was statistically significant (p=0.029). Conclusion: We concluded that a 20-minute application of 9.6% lidocaine is safe and effective for reducing pain associated with venipuncture.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.296-303
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• 2009

The effect of porosity on the high-cycle fatigue properties of Al-Si-Mg casting aluminum alloys was investigated in this study. Microstructure examination, tensile and high-cycle fatigue test were conducted on both Al-Si-Mg casted (F) and heat-treated (T6) conditions. Porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The microstructure observation results showed that eutectic Si particles were homogeneously dispersed in the matrix of the Al-Si-Mg casting alloys, but there were porosities formed as cast defects. The high-cycle fatigue results indicated that the fatigue strength of the 356-T6 alloy was higher than that of the 356-F alloys because of the significant reduction in volume fraction of pores by heat treatment. The SEM fractography results showed that porosity affected detrimental effect on the fatigue life: 80% of all tested samples fractured as a result of porosity which acted as the main crack initiation site. It was found that fatigue life decreased as the size of the surface pore increased. A comparison was made between surface pore and inner pore for its effect on the fatigue behavior. The results showed that the fatigue strength with the inner pores was higher than that of the surface pore.

• Journal of Welding and Joining
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• v.23 no.3
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• pp.61-67
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• 2005

Since lead (Pb)-free solders for electronics have higher melting points than that of eutectic Sn-Pb solder, they need higher soldering temperatures. In order to decrease the soldering temperature we tried to coat Sn-Bi layer on $Sn-3.5\%Ag$ solder by electroplating, which applies the mechanism of transient liquid phase bonding to soldering. During heating Bi will diffuse into the $Sn-3.5\%Ag$ solder and this results in decreasing soldering temperature. As bonding samples, the 1608 capacitor electroplated with Sn, and PCB, its surface was finished with electroless-plated Ni/Au, were selected. The $Sn-95.7\%Bi$ coated Sn-3.5Ag was supplied as a solder between the capacitor and PCB land. The samples were reflowed at $220^{\circ}C$, which was lower than that of normal reflow temperature, $240\~250^{\circ}C$, for the Pb-free. As experimental result, the joint of $Sn-95.7\%Bi$ coated Sn-3.5Ag showed high shear strength. In the as-reflowed state, the shear strength of the coated solder showed 58.8N, whereas those of commercial ones were 37.2N (Sn-37Pb), 31.4N (Sn-3Ag-0.5Cu), and 40.2N (Sn-8Zn-3Bi). After thermal shock of 1000 cycles between $-40^{\circ}C$ and $+125^{\circ}C$, shear strength of the coated solder showed 56.8N, whereas the previous commercial solders were in the range of 32.3N and 45.1N. As the microstructures, in the solder $Ag_3Sn$ intermetallic compound (IMC), and along the bonded interface $Ni_3Sn_4$ IMC were observed.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2000.04a
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• pp.73-73
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• 2000

Shear strength of BGA solder joints on Cu pad was studied for Cu-contained Sn n.5 a and 2.5wt.% Cu) and Sn-Pb (o.5wt.% Cu) solders, with emphasis on the roles of the C Cu-Sn intermetallic layer thickness and the roughness of the interface between the i intermetallic layer and solder. The shear strength test was performed both for a as-soldered s이der joints with soldering reaction times of 1, 2, 4 min and for aged s이der j joints at 170 C up to 16 days. The Cu addition to both pure Sn and eutectic Sn-Pb s solders increased the intermetallic layer thickness at both soldering and aging t temperatures. The Cu addition also resulted in changes in the roughness of the interface b between the intermetallic layer and solder at as-soldered states. With increasing Cu c content. the interface roughened for Sn-Cu solders whereas it flattened for Sn-Pb-Cu s solders. The shear fractures in all solder joints investigated were confined in the bulk s solder rather than through the intermetallic layer. Therefore, the effect of Cu content in s solders on the shear strength of the solder joints was primarily attributed to its i influence on the micros$\sigma$ucture of bulk solder, such as the size and spatial distributions of CU6Sn5 precipitates. In addition, the critical intermetallic layer thickness for a m maximum shear strength seemed to depend on the Cu content in bulk solder.older.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.186-193
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• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.303-316
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• 1987

The purpose f this study was to evaluate the effect of resin film thickness on the tensile bond strength and to compare the tensile bond strengths of 4 differently treated metal surfaces. For the experiment, seventy metal specimens were cast with Verabond and divided into I, II, III, groups. The metal specimens in group I were electrolytically etched and cemented with Panavia under finger pressure. Cement film thickness was regulated with metal spacers. The metal specimens in Group II were treated by 4 methods, such as electrolytic etching method, salt-roughened method, EZ-oxisor method , chemical etching method and cemented with Panavia. In group III, electrolytically etched metal specimens were cemented with Hy-Bond. The etched surface of metal specimens and the cement film thickness were examined under the scanning electron microscope. Results were as follows; 1. The tensile bond strength showed no significant difference between $30{\mu}m,\;80{\mu}m,\;130{\mu}m$ film thicknessspecimens. 2. There was no significant difference in the tensile bond strength between the 4 differently treated metal specimens. 3. The tensile bond strength showed significant difference between Panavia and Hy-Bond. 4. Scanning electron microscope photograph revealed that tile interdendritic eutectic was removed in electrolytically etched metal surfaces hilt even dendritic arm was removed in Chemically etched metal surfaces. 5. The metal surfaces which were air-abraded with $50{\mu}m$ aluminum oxide showed roughness and small crack on scanning electron microscope photograph.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.904-910
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• 2002

Surface alloying using TiC, $TiB_2$ and VC ceramic particles on carbon steel has been performed using high voltage electron beam. Each type of ceramic particles was mixed with flux of Al and $MgF_2$ in 1 to 4 ratio. The microstructures of the surface alloyed layers consisted of melted region, interface region. heat affected region and the unaffected matrix. The surface layer of the TiC surface alloyed had a cubed primary and a eutectic type of TiC. $TiB_2$ in surface layer of $TiB_2$ surface alloyed were incompletely melted with$ TiB_2$ particles as observed before the alloying. On the surface layer of the VC surface alloyed, very well defined cell structure was observed with VC on the cell boundary. In addition, ~50 nm in diameter VC particles in high density were ubiquitous in the matrix. Those fine VC particles prominently improved the hardness and wear resistance of the surface layer of the VC surface alloyed.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.897-903
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• 2002

Morphological evolution and growth mechanism at the solid/liquid interface during solidification were investigated in the Ni-base superalloy GTD111M by directional soldification and quenching(DSQ) technique. The experiments were conducted by changing solidification rate(V) and thermal gradient(G) which are major solidification process variables. High thermal gradient condition could be obtained by increasing the furnace temperature and closely attaching the heating and cooling zones in the Bridgeman type furnace. The dendritic/equiaxed transition was found in the G/V value lower than $0.05$\times$10{^3}^{\circ}C$s/$\textrm{mm}^2$, and the planar interface of the MC-${\gamma}$ eutectic was found under $17 $\times$ 10{^3}^{\circ}C$ s/$\textrm{mm}^2$. It was confirmed that the dendrite spacing depended on the cooling rate(GV), and the primary spacing was affected by the thermal gradient more than solidification rate. The dendrite lengths were decreased as increasing the thermal graditne, and the dendrite tip temperature was close to the liquidus temperature at $50 \mu\textrm{m}$/s.

• Journal of Korea Foundry Society
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• v.36 no.1
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• pp.1-9
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• 2016

Improvement of the mechanical properties of a commercial aluminium casting alloy, A356, was achieved through an optimised combination of alloying elements, modification, and heat treatment. 0.7 wt.% Cu and an additional 0.2 wt.% Mg were added to an Al-7Si-0.35Mg alloy for strengthening at both room and elevated temperatures, whilst a subsequent decrease in the ductility was compensated for by the modification of eutectic Si by Sr addition at a level of up to 110 ppm. It was found that the dissolution of Cu-rich or Mg-rich phases could be maximised by solid-solutionising an alloy with 40 ppm Sr at $530^{\circ}C$, increasing the tensile and yield strengths to 350 MPa and 297 MPa, respectively, with a reasonably high strain of 5% after peak-aging at $210^{\circ}C$. Further addition of Sr up to 110 ppm is, however, more likely to interfere with the dissolution of the Cu-rich or Mg-rich phases during solid solution treatment, resulting in a slight decrease in both tensile and yield strengths at room temperature. Besides the Cu addition, such undissolved phases, on the other hand, may contribute to elevated temperature strength at $200^{\circ}C$.