• Journal of Powder Materials
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• v.12 no.2 s.49
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• pp.131-135
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• 2005

7xxx series Al alloy has the most attractive properties including its excellent high specific strength, stress corrosion cracking and corrosion-resistance. However, in case of the Al-Zn system, the liquid phase has a transient aspect because of the high solid solubility of Zn in Al. Therefore, transient liquid phase sintering behavior was observed during the sintering process. And the amount of liquid and its duration were influenced by the process variables including heating rate and final sintering temperature. At high heating rates($100^{\circ}C/min$), the liquid fraction increased during sintering because diffusion was minimized and therefore local saturation could easily occur. The sintered density increased with increasing heating rate.

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.216-224
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• 1986

This paper treats the modelling and the control of the burnthrough point control system for an industrial sintering process. First, a state-space model is derived by defining new unconventional variables. A simple control law is proposed, which consists of the modified receding horizon control law and the least-squares prediction algorithm. The stability and the tracking properties of this control law are proved. The real-time experiments are carried out in a POSCO sintering plant and satisfactory results are presented in this paper. Before the real-time experiments, computer simulations are done and their results are also given for the comparison with the real-time experiments.

• Journal of Powder Materials
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• v.11 no.1
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• pp.69-73
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• 2004

The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

• Journal of Powder Materials
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• v.13 no.4 s.57
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• pp.269-277
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• 2006

[ ${\beta}-W(W_3O)$ ] oxide layer on the surface of each W(tungsten) nanopowder produced by the electric explosion of wire(EEW) process were formed during the 1vol.% air passivation process. The oxide layer hindered sintering densification of compacts during SPS process. The oxide phase was reduced to the pure W phase during SPS. The W nanopowder's compacts treated by the hydrogen reduction showed high sintered density of 94.5%. after SPS process at $1900^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.516-524
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• 2012

Selective Laser Sintering(SLS) system consists of various element technologies. Main components of the system include a position control system, a speed control system of the roller, and nitrogen atmosphere furtherance for the powdered sintering. Other systems which make the core of the SLS system are build room and the feed room for powder epitaxial, a temperature control system, and a scan path generator for the laser. The powder material for laser sintering is necessary to produce prototypes in Solid Freeform Fabrication(SFF) based on SLS process. This powder material is sintered in powder room using $CO_2$ laser after spreading evenly using roller to reproduce mold via SFF. This study addresses an SFF system by using the SLS process which applies single laser system to enable manufacturing of 3D shape. And to evaluate applicability of the single laser system, experiments were conducted with optimal fabricating process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.27-32
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• 2013

According to the composition of LTCC material, though it was thought that bulk defect which was made in forming process effects on the densification during the sintering, it was not reported systemically. In this study, we evaluated crystal structure, 3 point bending strength, hardness and microstructure of the samples by uniaxial pressing and tape casting using the commercial powders of the crystallizing glass and the glass/ceramic composite. In the case of glass/ceramic composite, Viox-001 powder with residual glass in the sintering, 3 point bending strength was similar regardless of forming process due to fill the bulk defect by residual glass. In the case of crystallizing glass, MLS-22, because glass phase was small in the sintering, glass did not fill the pore in the sample by uniaxial pressing process, therefore, the 3 point bending strength of it was 167 MPa. However, the 3 point bending strength of the sample by tape casting was 352 MPa and much higher. Meanwhile, crystal structure and hardness were similar regardless of forming process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.1
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• pp.6-12
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• 2015

Under rate-controlled sintering, furnace power is controlled to maintain a specific specimen contraction rate. This thermal processing method guarantees continuous process with a minimum thermal energy applied over time and makes it possible to control the density of the sintered body precisely. In this study, the rate-controlled sintering is applied to the sintering of $B_4C$ in order to investigate how rate-controlled sintering variables can affect the sintering behavior and/or grain growth behavior of $B_4C$ and how the results can be interpreted using sintering theories to draw an optimal sintering condition of the rate-controlled sintering. Further, the applicability of the rate-controlled sintering into the study for sintering of unknown materials is also considered.

• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.29-35
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• 2003

Anisotropic Sr-ferrites were prepared by the spark plasma sintering process (SPS). The Ferrite particles were oriented and densified during sintering process, and the anisotropic ferrites were manufactured at low sintering temperature and a remarkable short time processing by SPS method. It was showed that the anisotropy of ferrite particles at the specimen outer side was more higher than that at the specimen center, and it seems possible that the orientation of ferrite particles was related to DC current. Magnetic and physical properties of sintered Sr-ferrites are Br = 3.15 kG, iHc : 2.67 kOe, and density : 5.033 g/cm$^3$ when the samples were sintered for 8 minutes at 106$0^{\circ}C$.

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.55-60
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• 2009

In this study, Ti powder was fabricated from Ti scrap by a hydrogenation-dehydrogenation (HDH) method. The Ti powders were compacted by Spark plasma sintering (SPS) and the microstructure and mechanical properties of the powders were investigated. A hydrogenation reaction of Ti scrap occurred at temperatures near $450^{\circ}C$ with a sudden increase in the reaction temperature and a decrease in the pressure of the hydrogen gas as measured in a furnace during the hydrogenation process. In addition, a dehydrogenation process was carried out at $750^{\circ}C$ for 2hrs in a vacuum of $10^{-4}torr$. The Ti powder sizes obtained by hydrogenation-dehydrogenation and mechanical milling processes were in the range of $1{\sim}90{\mu}m$ and $1{\sim}100{\mu}m$, respectively. To fabricate Ti compacts, Ti powders were sintered under an applied uniaxial punch pressure of 40 MPa at in a range of $900{\sim}1200^{\circ}C$ for 5 min. The relative density of a SPSed compact was 99.6% at $1100^{\circ}C$, and the tensile strength decreased with an increase in the sintering temperature. However, the hardness increased as the sintering temperature increased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.59-66
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• 2019

In this study, we developed a novel laser sintering deposition system (LSDS) based on solid free-form fabrication (SFF) technology as it has the potential to fabricate complex geometries with controllable architecture for bone tissue engineering applications. The 3D biphasic calcium phosphate (BCP) scaffolds were fabricated with a pore size of 800㎛, a line width and height of 1000㎛, and an overall size of 8.2×8.2×8.0 mm3 according to the design of experiment (DOE) results. Additionally, an optimized manufacturing process using response surface analysis was established to fabricate 3D BCP scaffolds. The fabricated 3D BCP scaffolds were sintered at 950℃, 1050℃, 1150℃, and 1250℃ according to sintering processes with a furnace. As the sintering temperature increased, the porosity increased. Through the compressive strength test, the 3D BCP scaffolds sintered at 1050℃ presented good results of about 0.76 MPa. These results suggest that fabrication methods for 3D bioceramic scaffolds using LSDS may meet the basic requirements for bone tissue engineering.