• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.89-92
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• 2009

As a class of materials, Ni-base superalloys are among the most difficult metal alloys to forge together with refractory metals and cobalt-base superalloys. The mechanical properties of Ni-base superalloys depend very much on grain size and the strengthening phases, $\gamma$' ($Ni_3$(Al,Ti)-type) and $\gamma$".($Ni_3$Nb-type). Especially, the control of grain size remains as a sole means for the control of mechanical properties. The grain size and distribution changes of the wrought superalloys during hot working and heat treatment are mainly controlled by the recrystallization and grain growth behaviors. In this presentation, prediction technology of grain size through the computer-aided process design, and numerical modeling for predicting the microstructure evolution of Ni-base superalloy during hot working were introduced. Also, some case studies were dealt with actual forming processes of Ni-base superalloys.

• Transactions of Materials Processing
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• v.18 no.2
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• pp.166-171
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• 2009

In this paper, a basic study on micro cutting process with SM20C at low temperature environment was performed. In macro cutting fields, the cryogenic cutting process has been applied to cut the refractory metal but, the serious problem may be generated in micro cutting fields by the cryogenic environment. However, if the proper low temperature is applied to micro cutting area, the cooling effect of cutting heat is expected. Such effect can make the reduction of tool wear and burr formation. For verifying this possibility, the micro cutting experiment at low temperature was performed and SEM images were analyzed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.909-912
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• 2001

Lanthanide orthochromite materials have been widely studied as refractory conducting ceramics because of their electrical conductivity, oxidation resistance and high melting points. In this paper theoretical and experimental analysis about electric conductivity of the SHS prepared ceramics was carried out. The usefulness of the Seebeck-coefficient measurements as a function of P(O$_2$) is emphasized. Electronic conduction was found to be n-type in the lower P(O$_2$) range, and p-type in the higher P(O$_2$) range. The carrier concentrations were calculated as a function of P(O$_2$) and defect structure.

• Korean Journal of Agricultural Science
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• v.37 no.3
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• pp.465-469
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• 2010

In order to develop effective recycling technologies of disused railway wood ties, wood properties and residual creosote oil of wood ties were investigated. Among the total 50 wood ties, 32 wood ties were identified as tropical hardwood tree, such as, Keruing (Dipterocarpus spp.), Kempas (Koompassia malaccensis), Kapur (Dryobalanops spp.) Naytoh (Palaquium rostratum), and so on. Disused wood ties showed mostly sound structure without degradation of cell walls by decay fungi. Disused wood ties showed high strengths of bending and compressive parallel to grain because degradation of wood properties was hardly occurred in use under exterior condition. Disused railway wood ties had relatively poor depth of penetration and residual of creosote oil because of refractory wood structures. These results suggest that disused railway wood ties may be useful as recycling wood wastes.

• Carbon letters
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• v.2 no.1
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• pp.27-36
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• 2001

The pack-cementation process is the method which is formed SiC coating layer to improve weak oxidation properties of CFRCs (carbon fiber-reinforced carbons). This method develops the anti-oxidation coating layer having no dimensional changes and good wetting properties. In this study to improve the oxidative resistance of the prepared 4D CFRCs, the surface of CFRCs is coated by SiC using pack cementation method. The mechanical properties of SiC-coated 4D CFRCs are measured by the 3-point bending test, and their ablation properties are investigated by the arc torch plasma test. From the results, it is found that both mechanical and ablation properties of SiC-coated 4D CFRCs are much better than bare CFRCs.

• Advances in materials Research
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• v.2 no.3
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• pp.173-180
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• 2013

Lead-free complex perovskite ceramics $NaMeO_3$ ($Me{\equiv}Nb$, Ta) were synthesized using conventional solid state reaction technique and characterized by structural, FTIR and electrical (dielectric and ac conductivity) studies. The crystal symmetry, space group and unit cell dimensions were determined from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of single-phase orthorhombic structure with the space group Pmmm (47). Dielectric studies showed the diffuse phase transition at $394^{\circ}C$ for $NaNbO_3$ and $430^{\circ}C$ for $NaTaO_3$. Ac conductivity in both the compounds follows Jonscher's power law.

• Journal of Korea Foundry Society
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• v.17 no.1
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• pp.85-92
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• 1997

There has been a considerable interest to develop the silicide alloys as high temperature structural materials because of their excellent high temperature stability and strength, however, their lack of room temperature ductility and toughness was a main obstacle for the application. In order to improve ductility while maintaining good high temperature properties, possible refractory metal-silicide eutectic alloys composed of fine two phases were prepared by VAR(Vacuum Arc Remelting). Three silicide alloys, $Nb-Nb_3Si$, $Ti-Ti_5Si_3$, $V-V_3Si$, were selected as prospecting silicide eutectics and those high temperature characteristics were evaluated by high temperature compression test.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.493-501
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• 2012

A rotational force generator for molten metal is developed using a linear motor design technology. Also, the developed device is applied to reproduce aluminum scraps and easy to control the rotate, stop, and forward and reverse rotation of molten metal. In addition, the developed device improves the melting speed and reproduction rate about 250 (%) and 96-99 (%), respectively, compared to the conventional handmade methods. Because it generates almost no dusts, it can improve working environments in a factory. Also, it has no losses in energy because it directly melts scraps. The device generates small amounts of the loss in refractory materials and aluminum caused by its oxidation because the molten metal is continuously rotated in which the loss and oxidized aluminum are the problems in the conventional melting and holding furnaces. Thus, it is possible to extend the life of furnaces and to produce high quality aluminum products.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.6
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• pp.48-57
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• 1998

Abrasive waterjet(AWJ)은 가공시 열에 의한 가공경화가 없기 때문에 유리, 세라믹, 타이타늄및 금속복합재료와 같은 난삭재의 가공기술로 사용이 증가되었다. Acoustic emission(AE)신호에 의한 AWJ 세라믹 drilling가공시 On-Line Monitoring의 가능성이 고찰되었다. 기계 적인 물성이 서로 상이한 3종류의 세라믹이 본 연구에서 사용되었으며, AE신호는 AWJ drilling의 깊이를 monitoring하는데 유용함을 알 수 있었고 또한 세라믹의 material removal mechanisms을 규명하였다.

• Journal of the Korean Ceramic Society
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• v.52 no.2
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• pp.83-91
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• 2015

The redox reaction $M^{(x+n)+}+\frac{n}{2}O^{-2}{\rightleftarrows}M^{x+}+\frac{n}{4}O_2$ of multivalent ions in glass melts influences the melting process and final properties of the glass including the fining (removal of bubbles), infrared absorption and homogenization of melts, reaction between metal electrodes and melts or refractory and melts, and transmission and color of glass. In this review paper, the redox behaviors that occur frequently in the glass production process are introduced and the square wave voltammetry (SWV) is described in detail as an in situ method of examining the redox behavior of multivalent ions in the melt state. Finally, some voltammetry results for LCD glass melts are reviewed from the practical viewpoint of SWV.