• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.05a
• /
• pp.57-60
• /
• 2003

The purpose of this study is to investigate the high temperature deformation behavior of Ti-6Al-4V alloy and to predict the final microstructure under given forming conditions. Equiaxed and widmanstatten of Ti-6Al-4V alloys were prepared as initial microstructure and the compression tests were performed to obtain the flow curves at high temperatures (700∼1100$^{\circ}C$) and various strain rates (10$\^$-4/∼10$^2$/s). Form the results of compression test various parameters such as strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equations. To predict the final microstructure after forming, finite element analysis was performed considering the microstructural parameters such as the grain size and the volume fraction of second phase.

• Journal of Powder Materials
• /
• v.2 no.2
• /
• pp.149-157
• /
• 1995

In this study, an attempt was made to fabricate TiAl as well as its in situ composite via combustion synthesis. The processing variable of the combustion synthesis which include aluminum content and the heating rate were found to affect the combustion temperature. The combustion temperature measured, however, was lower than the melting temperature of TiAl and the reaction product were found to include incomplet reaction products. Carbon was added in order to increase the combustion temperature as well as to form in situ reinforcements. The reaction products showed homogeneous microstructures with carbide phases formed within indicating that the addition of carbon increased the combustion temperature above the melting temperature of TiAl.

• Korean Chemical Engineering Research
• /
• v.45 no.3
• /
• pp.215-218
• /
• 2007

The aim of this study is to test the feasibility of Pt/Al-MCM-41 for the dioxin decomposition reaction. For model reaction, 1,2-dichlorobenzene was decomposed instead of dioxin. $Pt/{\gamma}-Al_2O_3$ was compared with Pt/Al-MCM-41. Al-MCM-41 catlaysts were prepared by post grafting method and the Pt/Al-MCM-41 catalysts with Si/Al = 15, 30 showed higher catalytic activity than $Pt/{\gamma}-Al_2O_3$. Their higher catalytic activities were related with acid amounts. Especially Al-MCM-41 with ion exchanged with $H^+$ enhanced catalytic activity.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.10
• /
• pp.3258-3264
• /
• 2012

Aluminum oxide ($Al_2O_3$) nanofibers were treated thermally under an ammonia ($NH_3$) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of $Al_2O_3$/epoxy nanocomposites. The micro-structural and morphological properties of the $NH_3$-assisted thermally-treated $Al_2O_3$ nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and $N_2$/77 K isothermal adsorptions. From the results, the formation of AlN on $Al_2O_3$ nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified $Al_2O_3$ nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated $Al_2O_3$/epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.304.1-304.1
• /
• 2016

We have investigated the effect of plasma nitridation of atomic layer deposited-Al2O3 films of monocrystalline Si wafers and the thermal properties of nitridated Al2O3 films. Nitridation was performed on Al2O3 to form aluminum oxynitride (AlON) using NH3 plasma treatment in a plasma-enhanced chemical vapor deposition and it was conducted at temperature of $400^{\circ}C$ with various plasma power condition. After nitridation, we performed firing and forming gas annealing (FGA). For each step, we have observed the minority carrier lifetime and the implied Voc by using quasi-Steady-State photoconductance (QSSPC). We confirmed a tendency to increase the minority carrier lifetime and the implied Voc after the nitridation. On the other hand, the minority carrier lifetime and the implied Voc was decreased after Firing and forming gas annealing (FGA). To get more information, we studied properties of the plasma treated Al2O3 films by using Secondary Ion Mass Spectroscopy (SIMS) and X-ray Photoelectron Spectroscopy (XPS).

• Journal of the Korean Society for Heat Treatment
• /
• v.8 no.3
• /
• pp.236-243
• /
• 1995

Since amorphous alloys have been known to have better mechanical and chemical properties than crystalline alloys of the same composition, a great number of studies on the formation of Al-based amorphous alloys have been carried out actively. However, little has been obtained about the effect of Rare-Earth metal and Transition metal addition on amorphous phase formed by melt spinning method. This study included fabrication of amorphous alloy $Al_{85}Ce_5Ni_{10}$ by melt spinning methods and DTA, XRD, TEM analysis to determine crystalization behavoir. Annealing treatments were carried out in Ar atmosphere under isothermal and nonisothermal conditions. The diffraction pattern of non-heated ribbons showed broad form characteristic of glass metallic alloy. The crystallization of amorphous $Al_{85}Ce_5Ni_{10}$ takes place eutedtoidly by homogeneous formation of Al and MS-1, followed by precipitation of the $Al_{11}Ce_3$ and later $MS-1{\rightarrow}Al_3Ni$ transformation.

• Journal of Korea Foundry Society
• /
• v.29 no.6
• /
• pp.265-269
• /
• 2009

The optimum RRA heat treating conditions and SCC (stress corrosion cracking) resistance of semi-solid Al-Zn-Mg-Cu alloy fabricated by inclined cooling plate were compared with those of conventional mould cast alloys. The non-stirring method characterized by using a cooling plate can effectively eliminate dendritic structure and form a fine globular semisolid microstructure in as-cast Al-Zn-Mg-Cu alloy and the SCC resistance of semi-solid Al-Zn-Mg-Cu alloy was higher than that of conventional mold cast alloy. Also, after retrogressed treatment at RRA heat treatment of semi-solid Al-Zn-Mg-Cu alloy, retrogressed treatment time has increased more than 10 minutes at $180^{\circ}C$ to recovery the T6 heat treatment strength.

• Journal of Korea Foundry Society
• /
• v.12 no.6
• /
• pp.464-470
• /
• 1992

In the present study, the effects of Al/SiC interface reaction and the formation of $Al_4C_3$ compounds on the mechanical properties of the Al/SiC composites prepared by squeeze casting were investigated. After squeeze casting, the size of dendrites in Al without whiskers were larger than those with whiskers. The hardness of composite materials (about 72 Hv) was found to be approximating 40% higher than that of matrix metal (29Hv), which gradually increases which heat treatment Time showing maximum hardness at 12hr. The observation of increasing number of compounds in 12hrs heat treatment suggests that these compounds are responsible for the increase of hardness. By X-ray diffraction studies, those compounds were identified as $Al_4C_3$, (Al, Si). And intensity of Si peak increased. The tensile strengh of composite materials was gradually decresed by heat tretment, which was in contrast to the behavior of hardeness. With incresing heat tretment time, the fracture mode of composite materials was changed from large dimples and pull-out form of fiber to the fracture and rupture foum of fiber.

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

• 한국생물공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.723-729
• /
• 2003

Xenorhabdus nematophilus Kor-Al was cultured at flask and 5L jar fermentor at $28^{\circ}C$, 5% YS media condition. Antibiotic activity for X. nematophilus Kor-Al was experimented by paper disk method. As the result, antibiotic activity was growth associated form during culture time of X. nematophilus Kor-Al at flask. The maximum production and antibiotic activity were obtained at stationary period of cell growth. The optimum conditions of cell growth and antibiotic production at 5L jar fermentor were 400rpm agitation and 50% DO conditions.