• Journal of Korea Foundry Society
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• v.37 no.5
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• pp.148-156
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• 2017

The effects of minor additives on the casting properties of AC4A aluminum alloys were investigated. Measurements of the cooling curve and microstructure observations were conducted to analyze the effects of Ti-B and Sr minor elements during the solidification process. A fine grain size and an increase in the crystallization temperature for the ${\alpha}-Al$ solution were evident after the addition of 0.1wt% Al-5%Ti-1%B additive. The modification effect of the eutectic $Mg_2Si$ phase with the addition of 0.05% Al-10%Sr additive was prominent. A fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident. Fluidity, shrinkage and solidification-cracking tests were conducted to evaluate the castability of the alloy. The combined addition of Al-5%Ti-1%B and Al-10%Sr additives showed the maximum filling length owing to the effect of the fine ${\alpha}-Al$ grains. The macro-shrinkage ratio increased, while the micro-shrinkage ratio decreased with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives. The macro-shrinkage ratio was nearly identical, while the micro-shrinkage ratio increased with the addition of the Al-10%Sr additive. The tendency of the occurrence of solidification cracking decreased owing to the effect of the fine ${\alpha}-Al$ grains and the modification of the $Mg_2Si$ phase with the combined addition of Al-5%Ti-1%B and Al-10%Sr additives.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.827-831
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• 2008

Spark plasma sintering (SPS) of AlN ceramics were carried out with ${Y_2}{O_3}$ as sintering additive at a sintering temperature $1,550{\sim}1,700^{\circ}C$. The effect of ${Y_2}{O_3}$ addition on sintering behavior and thermal conductivity of AlN ceramics was studied. ${Y_2}{O_3}$ added AlN showed higher densification rate than pure AlN noticeably, but the formation of yttrium aluminates phases by the solid-state reaction of ${Y_2}{O_3}$ and ${Al_2}{O_3}$ existed on AlN surface could delay the densification during the sintering process. The thermal conductivity of AlN specimens was promoted by the addition of ${Y_2}{O_3}$ up to 3 wt% in spite of the formation of YAG secondary phase in AlN grain boundaries because ${Y_2}{O_3}$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. However, the thermal conductivity rather decreased over 3 wt% addition because an immoderate formation of YAG phases in grain boundary could decrease thermal conductivity by a phonon scattering surpassing the contribution of ${Y_2}{O_3}$ addition.

• Journal of Korea Foundry Society
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• v.24 no.6
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• pp.356-365
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• 2004

Mechanical properties and microstructures of the Ni-AI-Fe and Ni-AI-Fe-(B, Zr) alloys which containing $10{\sim}30at$.%Fe, 0.1at.%B and/or 0.1at.%Zr have been investigated. The experimental results showed that the microstructures of Ni25Al were changed from a single phase ${\gamma}$ to dual phase ${\gamma}$ and ${\beta}$ by addition of 27at.%Fe. Ni45Al, however, kept the single ${\beta}$ phase even though Fe was added upto 30at.%. The hardness of Ni25Al were increased from $H_RB$ 70 to $H_RC$ 39 by addition of 27at.%Fe. In the case of Ni45Al which have $H_RC$ 37, the hardness was decreased by lOat.%Fe addition, but increased with 30at.%Fe. The yield strength and ultimate compressive strength in the compressive test have showed a similar trend with the hardness change. The strain to fracture was 14% at maximum and achieved in Ni25Al-27at.%Fe and Ni25Al-27at.%Fe-0.1 at.%B alloys. The Ni45Al showed a relatively low strain to fracture as 4%. The impact absorption energy of Ni25Al increased from 0.74 kg-m to 1.81 kg-m by addition of 27at.%Fe. In case of Ni45Al, the addition of lOat.%Fe and lOat.%Fe with small amounts of Band Zr did not change significantly the impact absorption energy of 0.60 kg-m, whereas the addition of 30at.%Fe with small amounts of B and Zr increased it slightly. In fracture tests, both of two basic materials showed the same intergranular fracture but by adding Fe it changed to the cleavage fracture mode or co-existing of cleavage and intergranular fractures.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.375-381
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• 2005

High temperature oxidation behavior of thermal barrier coating (TBC) system (IN738 substrate + NiCoCrAlY or NiAl bond coat with or without Pt + yttria stabilized zirconia) prepared by air plasma spray (APS) process has been studied in order to understand the effect of Pt addition to bond coat on the stability of TBC system. Specimens were oxidized in thermal cycling and isothermal oxidation test at $1100^{\circ}C$. The Pt addition in TBC system with NiCoCrAlY bond coat showed a longer life time compared to that without addition of Pt. Pt addition to TBC system is believed to help the formation of more stable thermally grown oxide, $Al_2O_3$, at the TBC/bond coat interface, leading to a longer lifetime of TBC system.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.808-816
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• 1990

The thermal behavior of transformation and characteristics of seeded sample powders prepared by simultaneous $\alpha$-Al2O3 seed addition with water on the Al-sec-butoxide hydrolysis were studied. $\alpha$-Al2O3 seed particles are shown to act as nuclei for transformation of $\theta$-to $\alpha$-Al2O3 and to result in an increase in thetransformation kinetics and lowering of the transformation temperature by as much as 143$^{\circ}C$. Simultaneous seed addition on the hydrolysis resulted in uniform dispersin and creation of nucleation site on seed surface and only 0.1wt% seeding lowered the transformation temperature by as much as 115$^{\circ}C$. For 3wt% seed addition, $\alpha$-Al2O3 single phase was obtained at 95$0^{\circ}C$ for 100 minutes and the specific surface area of products were lowered to 11.9$m^2$/g as compared with that of $\alpha$-Al2O3 powder prepared without seed at 115$0^{\circ}C$ ; 15.1$m^2$/g due to depression of vermicular structure growth.

• 연구논문집
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• s.26
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• pp.103-112
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• 1996

$Al_2O_3/SiC$ Hybrid-Composite has been fabricated by conventional powder process. The addition of $\alpha-Al_2O_3$ as seed particles in the transformation of $\gamma-Al_2O_3 to $\alpha-Al_2O_3$ provided a homogeneity of the microstructure, resulting in increase of mechanical properties. The grain growth of $Al_2O_3$ are significantly surpressed by the addition of nano-sized. SiC particles, increasing in fracture strength. The addition of SiC plates to $Al_2O_3$ nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC plates with nitrides such as BN and /SiC$Si_3N_4$ enhanced fracture toughness much more than uncoated SiC plates by inducing crack deflection.

• Korean Journal of Materials Research
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• v.26 no.7
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• pp.376-381
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• 2016

For the development of a low-melting point filler metal for brazing aluminum alloy, we analyzed change of melting point and wettability with addition of Sn into Al-20Cu-10Si filler metal. DSC results showed that the addition of 5 wt% Sn into the Al-20Cu-10Si filler metal caused its liquidus temperature to decrease by about 30 oC. In the wettability test, spread area of melted Al-Cu-Si-Sn alloy is increased through the addition of Sn from 1 to 5 wt%. For the measuring of the mechanical properties of the joint region, Al 3003 plate is brazed by Al-20Cu-10Si-5Sn filler metal and the mechanical property is measured by tensile test. The results showed that the tensile strength of the joint region is higher than the tensile strength of Al 3003. Thus, failure occurred in the Al 3003 plate.

• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.248-255
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• 2010

The effect of various alloying elements and melt treatment on the microstructural control of Al-Sn metallic bearing alloy was investigated. The thickness of tin film crystallized around primary aluminum decreased with the addition of 5% Cu in Al-Sn alloy, with tin particles being reduced in size by intervening the Ostwald ripening. With the addition of Si in Al-10%Sn alloy, the tin particles were crystallized with eutectic silicon, resulting in uniform distribution of tin particles. With the addition of Cu and Si in Al-Sn alloy, both the tensile strength and yield strength increased, with the increasing rate of yield strength being less than that of tensile strength. Although the Al-10%Sn-7%Si alloy has similar tensile strength compared with Al-10%Sn-5%Cu, the former showed superior abrasion resistance, resulting from preventing the tin particles from movement to the abrasion surface.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.361-364
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• 2018

Binary Ti-Al alloys below 51.0 mass%Al content exhibit a breakaway, transferring from parabolic to linear rate law. The second $Al_2O_3$ layer might have some protectiveness before breakaway. Ti-63.1 mass%Al oxidized at 1173 K under parabolic law. Breakaway oxidation is observed in every alloy, except for Ti-63.1 mass%Al. After breakaway, oxidation rates of the binary TiAl alloys below 34.5 mass%Al obey almost linear kinetics. The corrosion rate of Ti-63.1 mass%Al appears to be almost parabolic. As content greater than 63.0 mass% is found to be necessary to form a protective alumina film. Addition of Mo improves the oxidation resistance dramatically. No breakaway is observed at 1123 K, and breakaway is delayed by Mo addition at 1173 K. At 1123 K, no breakaway, but a parabolic increase in mass gain, are observed in the Mo-added TiAl alloys. The binary Ti-34.5 mass%Al exhibits a transfer from parabolic to linear kinetics. At 1173 K, the binary alloys show vary fast linear oxidation and even the Mo-added alloys exhibit breakaway oxidation. The 2.0 mass%Mo-added TiAl exhibits a slope between linear and parabolic. At values of 4.0 and 6.0 mass% added TiAl alloys, slightly larger rates are observed than those for the parabolic rate law, even after breakaway. On those alloys, the second $Al_2O_3$ layer appears to be persistently continuous. Oxidation resistance is considerably degraded by the addition of Mn. Mn appears to have the effect of breaking the continuity of the second $Al_2O_3$ layer.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.106-112
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• 1995

In order to examine the effect of CuO and Al2O3 addition on the electrical conductivity of ZnO, both Al2O3 (0, 1, 2, 5, 10at.%) and CuO (1, 5at.%) were added to ZnO. Al2O3 addition (~2at.% Al) increased the total electrical conductivity of ZnO which was already decreased by CuO doping effect Above solid solubility of Al (~2at.%), ZnAl2O4 formed and the total electrical conductivity decreased due to the decrease of sintered density. Impedance measurements were used to know the reason and degree of contribution of three resistive elements, ZnO grain, ZnO/CuO, and ZnO/ZnO grain boundaries, to the total electrical conductivity changed.