• 한국주조공학회지
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• 제39권2호
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• pp.21-25
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• 2019

Microstructural and corresponding hardness changes of TiFe compounds with Zr (0~6 at%) or Ce (0~3 at%) were studied using samples prepared at different solidification rates. In arc-melted (TiFe)-Zr samples, the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases formed in the TiFe matrix, while in the (TiFe)-Ce sample, the $CeO_2$ phase formed along the grain boundary of the TiFe matrix. As the Zr content was increased, the volume fractions of the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases increased, forming a network structure. Accordingly, the hardness values of the samples also increased. With a small addition of Ce of approximately 0.1 at%, the as-cast microstructure could be effectively refined, reducing the average grain boundary diameter from ${\sim}100{\mu}m$ to ${\sim}14{\mu}m$. In the rapidly solidified sample prepared through a melt-spinning method, the constituent phases were identical to those of the arc-melted samples while the grains were refined. The microstructural changes of TiFe alloys can affect the hydrogen storage ability as well as the mobility of the hydrogen atoms in the alloys.

• Journal of Welding and Joining
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• 제25권5호
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• pp.45-50
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• 2007

The Ni-base superalloy GTD111 DS is used in the first stage blade of high power land-based gas turbines. Advanced repair technologies of the blade have been introduced to the gas turbine industry over recent years. The effect of the filler metal powder on Transient Liquid Phase bonding phenomenon and tensile mechanical properties was investigated on the GTD111 DS superalloy. At the filler metal powder N series, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid filler metal powder was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The bond strength of N series filler metal powder was over 1000 MPa. and ${\gamma}'$ phase size of N series TLP bonded region was similar with base metal by influence of Ti, Al elements. At the insert metal powder M series, the Si element fluidity of the filler metal was good but microstructure irregularity on bonded region because of excessive Si element. Nuclear of solids formed not only from the base metal near the bonded interlayer but also from the remained filler metal powder in the bonded interlayer. When the isothermal solidification was finished, the content of the elements in the boned interlayer was approximately equal to that of the base metal. But boride and silicide formed in the base metal near the bonded interlayer. And these boride decreased with the increasing of holding time. The bond strength of M series filler metal powder was about 400 MPa.

• 열처리공학회지
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• 제29권5호
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• pp.227-233
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• 2016

Phase transformation phenomenon at high temperature was investigated by using designed TiAl-Nb alloys with addition of the ${\beta}$ stabilizer. Examination of dendritic morphologies in arc-melted button ingot could reveal the crystallography of the primary solidification phase. It was found that the addition of ${\beta}$ stabilizer(Nb) shifted the high temperature region of the binary Ti-Al phase diagram to the high Al composition side so that ${\beta}$ phase forms as a primary crystal even at higher Al composition compared with the binary Ti-Al system. The ${\beta}$ was found to be the primary solidification phase for alloys with Al content less than about 52 at.%. The composition of ${\beta}$ solidification in Ti-Al-Nb ternary system could be determined from the partial liquidus projection which was constructed by observing the microstructure of arc-melted buttons. The Ti-46Al-(6, 8)Nb composition was selected for ${\beta}$ solidification and the directional solidification was performed by a floating zone-type DS apparatus at the growth rate 30 mm/hr respectively.

• 대한금속재료학회지
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• 제47권7호
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• pp.440-446
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• 2009

Co base superalloys have been widely used for the parts of gas turbine due to their excellent strength, thermal fatigue, oxidation resistance and weldability at high temperature. In this study, directional solidifications were carried out at various solidification rates, including $0.5{\sim}300{\mu}m/s$ in the Co base superalloy FSX-414. The cellular interface were formed at a low solidification rate, $1{\mu}m/s$, and the dendritic interface was found at higher solidification rates, $5{\sim}300{\mu}m/s$. As the spacing of dendrite structure decreased, the size and spacing of eutectics decreased. Dendrite arm spacing decreased with increasing solidification rates and temperature gradient. It was interesting to find the $M_{23}C_{6}$ eutectic microstructure formed between $\gamma$ dendrites. Composition analysis showed that Cr and W were segregated severely between the dendrites, which resulted in the formation of Cr-rich $M_{23}C_{6}$ and W-rich MC carbides.

• 한국주조공학회지
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• 제15권2호
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• pp.164-174
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• 1995

New metallic powder making processes, named "Centrifugal Emulsification Process(CEP)" and "Mixer and Settler(MS)" have been developed to synthesize rapid solidified metallic powders. Through CEP and MS processings, the high temperature metals as well as the low temperature alloys are manufactured. Also, the effects of rapid solidification on the undercooling, solidification rate and crystallization behaviors can be evaluated effectively through the processes. The standard deviations of the synthesized typical Pb-Sn eutectic powders are 1.63 and 1.51 for CEP and MS respectively, and the average size of the MS powders was $18{\mu}m$. The possibility of the customized not only size and shape control but microstructure control was also shown. Both of the new methods can be applied to continuous powder making processes.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.355-362
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• 2009

Most material of engineering interest undergoes solidification process from liquid to solid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material which governs the physical properties of final product. In this paper, we expand our previous two-dimensional numerical technique to three-dimensional simulation for computing dendritic solidification process with fluid convection. We used Level Contour Reconstruction Method to track the moving liquid-solid interface and Sharp Interface Technique to correctly implement phase changing boundary condition. Three-dimensional results showed clear difference compared to two-dimensional simulation on tip growth rate and velocity.

• 한국주조공학회지
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• 제9권1호
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• pp.73-79
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• 1989

Microstructural characteristics of Al-3.63wt.%Pb hyper-monotectic alloy rapidly-solidified by melt spinning were examined. Possibility of forming a planar liquid -solid interface during rapid solidification of this alloy was also considered with a morphological stability theory, and a mechanism of forming banded structure observed at the bottom parts of melt-spinned specimens was considered as well. Application of the absolute stability criterion predicts the liquid-solid interface of the primary aluminium phase to be able to maintain a planar interface during the early stage of rapid solidification. Formation of banded structure was supposed to be resulted from the release of latent heat during solidification, which affect the stability of a planar liquid-solid interface.

• 한국주조공학회지
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• 제29권1호
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• pp.38-44
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• 2009

Magnetic separation of Fe contaminated Al-Si cutting chip scraps was performed for the recyclability assessment. It was also aimed to investigate the casting and solidification characteristics of the cutting chip scraps. The magnetically separated cutting chip scraps were adequately treated for the casting procedure and test specimens were made into a stepped mold inducing different cooling rates. The test specimens were evaluated by the combined analysis of ICP, Spectroscopy, OM-image analyzer, SEM/EDS, etc. Solidification characteristics of cutting chip scraps were examined as functions of Fe content and cooling rate. It is concluded that the magnetic separation process can be utilized to recycle the Fe contaminated Al-Si cutting chip scraps in the high cooling rate foundry process.

• 대한기계학회논문집B
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• 제33권7호
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• pp.469-476
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• 2009

Most material of engineering interest undergoes solidification process from liquid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material thus the physical properties of final product. In this paper, effect of fluid convection on the dendrite solidification morphology is studied using Level Contour Reconstruction Method. Sharp interface technique is used to implement correct boundary condition for moving solid interface. The results showed good agreement with exact boundary integral solution and compared well with other numerical techniques. Effects of Peclet number and undercooling on growth of dendrite tip of both single and multiple seeds have been also investigated.

• 한국세라믹학회지
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• 제36권7호
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• pp.725-733
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• 1999

It is a fundamental experiment to use blast-furnace slag in solidification/stabilization process. The compressive strength and leaching test of Pb and Cr doped samples were evaluated and the effects of heavy-metal ions on the hydration of slag was investigated. Sodium silicates(5wt%) was added as alkali-activator and the effects of replacing a part of slag with flyash or gypsum was also discussed. Pb ion was solidified by encapsulation of matrix. In of slag${\pm}$gypsum binder microstructure was densified by accelerating to form AFt/AFm phase and compressive strength was improved resulting in reducing leaching amount of Pb ion. Cr ion was solidified by substituting with Al ion in aluminate product. Slag+fly ash binder improved compressive strength and decreased leaching amount of Cr ion.