• Proceedings of the KWS Conference
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• 2010.05a
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• pp.22-22
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• 2010

Eutectic composition phase with low melting point which solidifies at the final stage affects the solidification cracking at the intercellular or interdendritic area of welds and castings. If sufficient amount of eutectic composition liquid does not exist between the solidifying phases, the discontinuities remain as cracks. However, abundant amount of liquid eutectic composition existing in the final stage can flow into the discontinuities easily and heal the cracks. By flowing of liquid eutectic and healing of discontinuities, the possibility of cracking can be reduced when the amount of eutectic liquid is sufficient. For the solidification of pure metals, liquid eutectic does not exist and the interlocking of growing solid phases can be realized without interruption of liquid film. Therefore there is little possibility of solidification cracking in the case of welds and castings of pure metal. In a practical sense, the effective way to reduce or prevent the solidification cracking is making the composition of molten pool or melts near to the eutectic composition.

• 연구논문집
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• s.25
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• pp.163-168
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• 1995

The intermetallic compound $Ni_3Al$ causes a peritectic reaction at the composition and temperature very close to the eutectic reaction in Ni-Al system. Although the phase diagram accepted for this system by ASM Handbook has the eutectic forming between the $\gamma$ and $\gamma$ phases, directional solidification study has shown that the eutectic occurs between $\beta$ and $\gamma$. This work examines the liquidus region using quenched, directional solidification experiments that preserve the microstructrues formed at the solidification front. It is also shown that under certain composition and growth conditions a metastable eutectic between the $\beta$ and $\gamma$ phases forms in this system. Finding of the metastable eutectic provided an important information to understand the phase equilibria near the $Ni_3Al$ composition.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.59-66
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• 2000

To investigate the optimum brazing condition, variation of bonded structure and mechanical properties of novel brazed pure Al with bonding condition (brazing temperature, time and Si/flux ratio) was studied. A basic study of the bonding mechanism was also examined. The optimum brazing condition was obtained at $590^{\circ}$ for 2 minutes and the bonded structure showed that it is composed of almost entirely eutectic Al-Si with near eutectic composition. At higher brazing temperature $630^{\circ}$, hypoeutectic Al-Si structure was observed in the bonded area and resulted in erosion of base metal. The thickness of eutectic layer formed in optimum brazing temperature increased linearly with the square root of time, showing a general diffusion controlled process. The ultimate tensile strength of bonded joint brazed at an optimum brazing condition was about 60% of base metal and its fracture surface showed a brittle mode.

• Journal of Korea Foundry Society
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• v.4 no.4
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• pp.14-19
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• 1984

In order to clarify the solidification mechanism of Al-Si alloy, Mushy Degree of Eutectic Solidification (MDE) and Centerline Feeding Resistance (CFR) were systematically studied by casting with various compositions of $Al-(6{\sim}18%)$ Si alloys into several kinds of molds having different cooling rates. The results are as follows: 1. CFR% increases slightly as solute concentration increases, but decreases remarkably as the cooling rate of the mold increases, that is, the composition dependence of the alloys has more effect on the change of CFR% than that of the mold cooling rate. 2. The composition dependence of MDE value has the same tendency as that of Degree of Eutectic Solidification (DES). MDE value within the range of hypereutectic composition is larger than that of hypoeutectic and it represents the maximum value at eutectic composition. The higher the cooling rate is, the less the MDE value is.

• Journal of Korea Foundry Society
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• v.35 no.6
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• pp.178-184
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• 2015

Due to excellent abrasion resistance the high-chrome white irons are widely used in mining and mineral industries. Minor variation of carbon content in 28% chrome white iron resulted in difference in primarily solidified microstructure. Sub-eutectic (hypoeutectic) composition led to formation of primarily solidified dendrites. Formation of primarily solidified dendrites which were supersaturated with carbon and chrome also caused precipitation of fine secondary carbides that are different from relatively large plate type $M_7C_3$ carbides in the eutectic structure. Small portion of primarily solidified dendrite expected to contribute significantly to the improvement of abrasion resistance of the white iron because the dendrites provided mechanical support to carbides. The relative fraction of primary dendrite increased with reduction of carbon content from the eutectic composition. The increased fraction of primary dendrite increased hardness value of the white irons.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.859-860
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• 2006

TiC-$TiB_2$-SiC system was a ternary eutectic, whose eutectic composition was 34TiC-$22TiB_2$-44SiC (mol%). TiC-$TiB_2$-SiC ternary eutectic composite were synthesized by a floating zone method using TiC, $TiB_2$ and SiC powders as starting materials. The TiC-$TiB_2$-SiC eutectic composite showed a lamellar texture. TiC(022), $TiB_2(010)$ and SiC(111) of the eutectic composite were perpendicular to the growth direction. TiC-$TiB_2$-SiC ternary eutectic composite had specific relationship among the crystal planes: TiC[011]//$TiB_2[010]$//SiC[112], TiC(200)//$TiB_2$(001)//SiC(402) and $TiC(1\bar{1}1)$//$TiB_2(101)$//SiC(220).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2367-2374
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• 1996

A generalized Scheil equation for the solute redistribution in the absence of the back diffusion during the dendritic solidification of binary alloys is derived, in which coarsening of the secondary dendrite arms is taken into account. The obtained equation essentially includes the original Scheil equation as a subset. Calculated results for typical cases show that the coarsening affects the microsegregation significantly. The eutectic fraction predicted for coarsening is considerably smaller than that for fixed arm spacing. The most important feature of the present equation in comparison with the Scheil equation lies in the fact that there exists a lower limit of the initial composition below which the eutectic is not formed. Based on the generalized Scheil equation and the lever rule, a new regime map of the eutectic formation on the initial composition-equilibrium partition coefficient plane is proposed. The map consists of three regimes: the eutectic not formed, conditionally formed and unconditionally formed, bounded by the solubility and diffusion controlled limit lines.

• Bulletin of the Korean Chemical Society
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• v.7 no.5
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• pp.353-357
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• 1986

Mutual miscibility between thermotropic, nematic compounds with two terminal mesogenic units and a central spacer was studied by differential scanning calorimetry (DSC) and on a polarizing microscope. It was found that the isomorphous, nematic dimesogenic compounds with wide variety of structures are miscible in mesophases with each other over the whole range of composition and that Schroder-van Laar equation almost correctly predicts the melting temperature and composition of eutectic mixtures. There was a pair of compounds which were exceptional and did not form a eutectic mixture and, instead, revealed a monotonous change in melting (T$_{m}$) and isotropic transition temperatures (T$_{i}$) as the composition of the mixture was varied. The compounds were of almost same structure in shape and seemed to undergo formation of solid solution.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.678-686
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• 2020

Microstructural characteristics of directionally solidified René 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 ℃), MC carbide (1,278 ℃), γ/γ' eutectic phase (1,202 ℃), and γ' precipitate (1,136 ℃) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of René 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.

• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.13-20
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• 1986

Composite polycrystals including ${\gamma}$-$6Bi_2O_3$.$SiO_2$ crystal which have needlelike regular structure are useful for the high resolution optical devices. For the purpose of obtaining the composite polycrystals described above the melts of eutectic composition in the three eutectic systems including $6Bi_2O_3$.$SiO_2$ composition were unidirectionally solidified at a rate of 0.05 and 0.25 cm/h under a thermal gradient of 10$0^{\circ}C$/m. Composite polycrystals of relatively regular structure in which needlelike ${\gamma}$-$6Bi_2O_3$.$SiO_2$ crystals were arrayed in parallel with $2Bi_2O_3$.$B_2O_3$ crystal matrix were obtained when the eutectic melt of $6Bi_2O_3$.$SiO_2 -2Bi_2O_3$.$B_2O_3$ system was solidified at a rate of 0.25 cm/h. Partial structural irregularity however was found in the obtained composite polycrystals.