• Progress in Superconductivity
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• v.9 no.1
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• pp.1-4
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• 2007

The most common technique to fabricate $MgB_2$ superconducting wire is by powder-in-tube (PIT) technique. Therefore, the starting powder for the processing of $MgB_2$ superconductors is an important factor influencing the superconducting properties and performance of the conductors. In this study, the influence of magnesium precursor powders and annealing temperatures on the transition temperatures ($T_c$) and critical current densities ($J_c$) of $MgB_2/Fe$ wires was investigated. All the $MgB_2/Fe$ wires were fabricated by in situ PIT process. It was found that higher $J_c$ was obtained for $MgB_2$ wires with smaller particle size of magnesium precursor powders. The $J_c$ also increases with decreasing annealing temperatures.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.271-280
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on optical microstructure, hardness and wear characteristics of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite appear in outermost surface layer with fine martensite in inside hardened zone. Hardness measurements have revealed that the range of maximun hardness value is $Hv=650{\pm}15$ and as the power density increases and the traverse speed decreses, the depth of hardened zone increases due to as increase in input power density. Wear test has exhibited that wear rasistance of laser surface hardened specimen is superier compared to that of untreated specimen under the condition of same load at a given sliding distance, showing that absorption results of an wxidized substance due to a heavy abrasion appear in untreated specimen. The amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load decreses with increasing traverse speed at a given power density and with increasing power density at a given traverse speed.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.1
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• pp.3-9
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• 2010

Titanium and its alloys were brazed in the range of $850-950^{\circ}C$ within 10 min. of brazing time using expensive infra red or other heating methods. However, brazing time needs to be extended to get temperature-uniformity for mass production by using continuous belt type furnace or high vacuum furnace with low heating rate. This study examined effects of holding temperature for 60 min, on microstructure and mechanical properties of titanium alloys. Mechanical properties of titanium alloys were drastically deteriorated with increasing holding temperature followed by grain growth. Maximum holding temperatures for CP (commercial pure) titanium and Ti-6Al-4V were confirmed as $800^{\circ}C$ and $850^{\circ}C$, respectively. Both titanium alloys were successfully brazed at $800^{\circ}C$ for 60 min. with the level of base metal strengths by using Zr based filler metal, $Zr_{54}Ti_{22}Ni_{16}Cu_8$.

• Journal of Korea Foundry Society
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• v.34 no.1
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• pp.1-5
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• 2014

The austempering transformation behavior in Fe-0.7wt.%C-2.3wt.%Si-0.3wt.%Mn steel is investigated. Each specimen was austenitized for 60 min at $900^{\circ}C$, and austempered at $380^{\circ}C$ for different time periods varying from 2 min to 256 min. After the austempering heat treatment, the Stage I and II evolutions are performed using optical metallography, X-ray diffraction and image analyses. Variations in the X-ray diffraction patterns and lattice parameters of the ferrite and austenite demonstrate that the residual austenite decomposes into ferrite and carbide during the Stage II evolution; moreover the amount of ferrite increases during the Stage I evolution. While the amount of austenite increases during Stage I, it dicreases during Stage II. Overall, the variations in the volume fractions of the microstructure and carbide formation in stages I and II meet high temperature austempering reaction of the ausferrite microstructure.

• Journal of the Korea Organic Resources Recycling Association
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• v.15 no.4
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• pp.100-106
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• 2007

In this paper, first we went through the deliming and degreasing as pre-treatment of limed pelt scrap which is derived from liming process during leather manufacturing processing. After that, we produced fine collagen using non-chrome tanning and heat treatment and using acryl monomer graft polymerization such as GMA and MMA. From the comparisonof final products made by various methods, they showed good features in pyrolysis temperature, heat-resisting, variation of moisture content and particle distribution.

• Journal of the Korean Chemical Society
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• v.41 no.3
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• pp.130-137
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• 1997

Powders and thin-layers of a hexagonal titanium disulfide phase have been successfully prepared by modifying the sol-gel process. The reaction of titanium isopropoxide with hydrogen sulfide causes the precipitation of a precursor which was converted to the disulfide on heat-treatment in $H_2S$ at various temperatures depending on the solvent adopted, whereas that of titanium 2-methoxyethoxide with $H_2S$ produces a stable solution which was spin-casted onto silicon substrates followed by thermolysis to give thin films. Upon heat-treatment in $H_2S$, the disulfides show interesting morphological variations in the form of their powders and thin films, which were characterized by SEM and X-ray diffractometer.

• Journal of Korea Foundry Society
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• v.40 no.3
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• pp.76-84
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• 2020

The effects of Alloying Element and Heat Treatment on the mechanical properties of ductile cast iron poured into shell stack molds were investigated. The strength and hardness were increased and the elongation was decreased roughly with the increased amounts of tin and copper added, respectively. Those were greatly increased with the increased amount of tin added and the elongation was roughly decreased with it. In the simultaneous addition of copper and tin, the strength and hardness of the tin increased, but the elongation rate decreased. Those were greatly increased and this was decreased with normalizing. In the case of specimens with smaller section sizes during austempering processing, the strength and hardness were higher than those with larger sections, but the elongation rate was lower.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.53-58
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• 2004

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment were investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) were hot extruded to make T-shape bars at extrusion temperature of $380^{\circ}C$, then the bars were solution treated at $480^{\circ}C$ for 2hrs followed by artificial aging at $120^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consisted of elongated grains, however, fine equiaxed grains were also observed around surface. The microstructural gradient suggested that different restoration process could proceed during the hot extrusion. For B1 and B2, different grain growth behaviors were found around the surface during the post heat treatment. Rapid grain growth behavior was observed for B1 around the surface, however, it was not observed for B2. Orientation pinning, which was related with the evolution of preferred orientation, and precipitation were thought to be responsible for the rapid grain growth.

• Transactions of Materials Processing
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• v.20 no.7
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• pp.512-517
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• 2011

TRB(Tailor Rolled Blank) is an emerging manufacturing technology by which engineers are able to change blank thickness continuously within a sheet metal. TRB door inner panels with required larger thicknesses can be used to support localized high loads. In this study, the aluminum alloy 5J32 TRB sheet is used for a door inner panel application. The TRB material properties were varied by using three heat treatment conditions. In order to predict the failure of the aluminum TRB during simulation, the forming limit diagram, which is used in sheet metal forming analysis to determine the criterion for failure, was investigated. Full-field photogrammetric measurement of the TRB deformation was performed with an ARAMIS 3D system. A FE model of the door inner panel was created using Autoform software. The material properties obtained from the tensile tests were used in the numerical model to simulate the door inner of AA 5J32 for each heat treatment condition. After finite element analysis for the evaluation of formability, a prototype front door panel was manufactured using a hydraulic press.

• Journal of the Korean Ceramic Society
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• v.33 no.10
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• pp.1170-1176
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• 1996

Porous silicon was prepared by anodic reaction. The process was controlled by current density and etching time an the thickness change and the room temperature PL was measured. The thickness of porous silicon was increased with etching time and was decreased after critical time. It was the same as increasing current density. It needed only 15 sec to electropolish the surface of porous silicon above current density 70 mA/cm2. We can understand that increasing etching time leads narrow size of Si column by porous silicon formation mechanism. And the sample with narrow Si column revealed PL blue shift. The specimens were heated in the range of 300-1000$^{\circ}C$ in order to see PL changes. The heat treatment was proceeded in H2 atmosphere vacuum system to avoid oxidation. The PL was disappeared above 600$^{\circ}C$. In high temperature some sintered Si columns were observed in SEM photography. There was no difference of -Hx bonds which was suggested as evidence of hydride compounds luminescence between 500$^{\circ}C$ and 600$^{\circ}C$. Thus it is concluded that quantum confinement is major factor of PL of porous silicon.