• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.503-506
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• 2002

BSCCO 2212 HTS was fabricated by CFP(centrifugal forming process). The powder was initially ground in the mixing ratio of 2:2::1:2 with 10% of SrSO$_4$. The temperature increased up to 1035$^{\circ}C$ and 1200$^{\circ}C$ for melting. The melt was poured into the preheated and rotating copper mould from 200 to 600$^{\circ}C$. The specimen was not broken by thermal impact when the melting temperature was over 1050$^{\circ}C$ and copper mould was preheated over 400$^{\circ}C$ for 30min. A tube type of specimen was annealed at 840$^{\circ}C$ or 860$^{\circ}C$ in oxygen atmosphere for 24hours. Typical microstructure was analyzed in terms of CFP parameters by XRD, SEM, and EDS and also superconducting characteristics were compared.

• Laser Solutions
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• v.7 no.1
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• pp.37-47
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• 2004

Laser-assisted selective infiltration is a new method of building metal layers to make metal parts layer by layer, in which superheated microscopic metal droplets are infiltrated into a laser-preheated layer of microscopic metal powders. In this work, the selective infiltration of a low melting-point metal, Sn-37Pb wt%, was conducted to investigate the effects of such dominant parameters as superheating temperature, Nd:YAG laser power for preheating, substrate temperature, etc. The optimal conditions for successful selective infiltration of a single layer of microscopic metal powder were experimentally obtained

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.12-15
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• 2003

The YBaCuO thick film was deposited by the electrophoresis in the solution with different dimension particles. The morphology of the films deposited from different particles size was compared. The powder made by sol-gel method has the submicron particles, which deposit the most smooth film, and without microcracks after sintering. After sintering of the deposited film, the zone-melting process was carried out in low oxygen partial pressure (100 Pa) and Ag was used as substrate. And the zone-melted YBaCuO was studied by XRD.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.72-75
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• 2003

HTS tubes were fabricated in terms of various SrSO4 additions by Centrifugal Forming Method. For powder melting by induction, the optimum temperature ranges of melting and preheating were 105$0^{\circ}C$~110$0^{\circ}C$ and 55$0^{\circ}C$ for 30min respectively The mould rotating speed was 1000rpm. A tube was annealed at 84 $0^{\circ}C$ for 72 hours in oxygen atmosphere. The plates like grains more than 20${\mu}{\textrm}{m}$ were well developed along the rotating direction of mould regardless of the amounts of SrSO4 in Bi2212. The measured Ic and Jc at 77K(B = 0T) in Bi2212 with 7％ SrSO4 composition were about 680A and 380A/$\textrm{cm}^2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.527-530
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• 2004

High-temperature Superconductor(HTS) tubes were fabricated in term of different diameter, length and thickness by centrigugal forming method. For powder melting by induction the optimum range of melting temperatures and preheating temperature were $1050^{\circ}C{\sim}1100^{\circ}C\;amd\;550^{\circ}C$ for 30min, respectively. The mould renting speed was 1000rpm. A tube was annealed at $840^{\circ}C$ for 72hours in oxygen atmosphere. The plate-like grains were well developed along the renting direction and typical grain size was about more than $40{\mu}m$. It was found that Ic values increased with increasing the tube diameter while the Ic decreased with increasing tube thickness. Also Ic decreased with increasing the tube length. The measured Ic in $50mm{\times}70mm{\times}25mm$ tube was about 896Amp.

• Journal of Powder Materials
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• v.28 no.6
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• pp.491-496
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• 2021

The process optimization of directed energy deposition (DED) has become imperative in the manufacture of reliable products. However, an energy-density-based approach without a sufficient powder feed rate hinders the attainment of an appropriate processing window for DED-processed materials. Optimizing the processing of DED-processed Ti-6Al- 4V alloys using energy per unit area (E_eff) and powder deposition density (PDD_eff) as parameters helps overcome this problem in the present work. The experimental results show a lack of fusion, complete melting, and overmelting regions, which can be differentiated using energy per unit mass as a measure. Moreover, the optimized processing window (E_eff = 44~47 J/mm² and PDD_eff = 0.002~0.0025 g/mm²) is located within the complete melting region. This result shows that the Eeff and PDDeff-based processing optimization methodology is effective for estimating the properties of DED-processed materials.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.175-176
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• 2022

By studying the characteristics of matrix insulated through heat generated through oxidation of iron powder, the basic research results on the possibility of buffering and applicability of Cold weather concrete as a curing method are presented. In order to prevent freezing due to a sharp decrease in temperature in the initial stage of curing, iron powder (Fe), powder activated carbon, which is a small amount of porous carbonaceous adsorbent, and salt (NaCl) as an oxidizing agent are replaced with iron powder admixture. As the curing temperature increases, the strength tends to increase, and when replacing the admixture at the same curing temperature, the strength slightly decreases. This is determined as a result of generating iron oxide through an oxidation reaction of iron powder, activated carbon, and NaCl generating a large amount of pores in the matrix. In addition, the internal temperature tends to increase as the mixing substitution rate increases, and it is judged that the oxidation heat of the iron powder mixture affects the increase of the internal temperature during curing. The higher the replacement rate of the iron powder mixture, the slightly lower the strength, but it is determined that freezing and melting that may occur in the early stage of curing can be prevented due to an increase in the initial internal temperature.

• ETRI Journal
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• v.32 no.3
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• pp.414-421
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• 2010

The interconnection mechanisms of a smart anisotropic conductive adhesive (ACA) during processing have been characterized. For an understanding of chemorheological mechanisms between the fluxing polymer and solder powder, a thermal analysis as well as solder wetting and coalescence experiments were conducted. The compatibility between the viscosity of the fluxing polymer and melting temperature of solder was characterized to optimize the processing cycle. A fluxing agent was also used to remove the oxide layer performed on the surface of the solder. Based on these chemorheological phenomena of the fluxing polymer and solder, an optimum polymer system and its processing cycle were designed for high performance and reliability in an electrical interconnection system. In the present research, a bonding mechanism of the smart ACA with a polymer spacer ball to control the gap between both substrates is newly proposed and investigated. The solder powder was used as a conductive material instead of polymer-based spherical conductive particles in a conventional anisotropic conductive film.

• Transactions of Materials Processing
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• v.25 no.6
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• pp.353-358
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• 2016

Direct energy deposition (DED) is an additive manufacturing technique that involves the melting of metal powder with a high-powered laser beam and is used to build a variety of components. In recent year, it can be widely used in order to produce hard, wear resistant and/or corrosion resistant surface layers of metallic mechanical parts, such as dies and molds. For the purpose of the hardfacing to achieve high wear resistance and hardness, application of high speed steel (HSS) can be expected to improve the tool life. During the DED process using the high-carbon steel, however, defects (delamination or cracking) can be induced by rapid solidification of the molten powder. Thus, substrate preheating is generally adopted to reduce the deposition defect. While the substrate preheating ensures defect-free deposition, it is important to select the optimal preheating temperature since it also affects the microstructure evolution and mechanical properties. In this study, AISI M4 powder was deposited on the AISI 1045 substrate preheated at different temperatures (room temperature to $500^{\circ}C$). In addition, the micro-hardness distribution, cooling rates, and microstructures of the deposited layers were investigated in order to observe the influence of the substrate preheating on the mechanical and metallurgical properties.

• Journal of Powder Materials
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• v.28 no.5
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• pp.410-416
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• 2021

Ti-6Al-4V alloy has a wide range of applications, ranging from turbine blades that require smooth surfaces for aerodynamic purposes to biomedical implants, where a certain surface roughness promotes biomedical compatibility. Therefore, it would be advantageous if the high volumetric density is maintained while controlling the surface roughness during the LPBF of Ti-6Al-4V. In this study, the volumetric energy density is varied by independently changing the laser power and scan speed to document the changes in the relative sample density and surface roughness. The results where the energy density is similar but the process parameters are different are compared. For comparable energy density but higher laser power and scan speed, the relative density remained similar at approximately 99%. However, the surface roughness varies, and the maximum increase rate is approximately 172%. To investigate the cause of the increased surface roughness, a nonlinear finite element heat transfer analysis is performed to compare the maximum temperature, cooling rate, and lifetime of the melt pool with different process parameters.