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Morphological evolution and growth mechanism of MC carbide during solidification of Ni-base superalloy Mar-M247LC were investigated by directional solidification and quenching(DSQ) at various solidification rates. The stoichiometry of the MC type carbide was identified as (Hf, W, Ta)₂TiC₃ by EPMA. The morphology of the carbides showed a big difference between those formed at relatively low solidification rates of 0.8×10^(-6) m/s ∼ 2×10^(-6) m/s and high solidification rates of 5×10^(-6) m/s ∼ 15×10^(-6) m/s. As increasing the solidification rate, carbide morphology was transformed from equilibrium octahedron shape to complex dendritic shape. At low solidification rate, carbide growth occurred by a layered growth from steps on the {111} facets. When the carbide growth rate increased, some γ layer was incorporated into growing carbide to form a layered composite structure. The carbide morphologies were also determined according to positions and shapes of the mushy zone.

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Methodologies both to avoid the formation of Al₄C₃ and to tailor the interfacial structures in the SiC/2014Al composite were demonstrated. Modification of the interfacial structures in the SiC/2014Al composite were made by forming SiO₂ layers on the surfaces of SiC via the passive oxidation at elevated temperatures. In the 2014Al composite reinforced oxidized SiC, nano-sized MgAl₂O₄ and Si crystals were observed to form at the interfacial region as a result of the reaction between the SiO₂ layer and the matrix. On the other hand, in the case of the 2014Al composite reinforced unoxidized SiC, SiC were found to react with Al to form both Al₄C₃ and Si. Crystallographic structures of the observed interfacial products were characterized using EDS and CBED of TEM.

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Nanocrystalline Al-Ti alloy powders were produced by the reactive ball milling and subsequently consolidated by the plasma activated sintering(PAS). The consolidation behavior of the powder with pressure, temperature and time was investigated by densimeter, SEM and TEM. Al-Al₃Ti alloy powders were produced after degassing treatment at 500℃ and these alloy powders maintained the grain sizes of about 20㎚ nearly equal to those of the as-milled powders. Nanocrystalline Al-Al_3Ti alloy powders were fully consolidated to the relative density of about 99% and the grain sizes maintained to the order of 50∼100㎚ under the condition of 75MPa, 500℃ and 60s which is considered to be the optimum consolidation condition of PAS process. TEM analysis of PAS consolidated Al-Al_3Ti alloys showed more uniform and finer grain sizes in very short consolidation times than the Al-Ti alloys consolidated by conventional vacuum hot pressing and hot extrusion.

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Microstructural evolution of Ti-C-metal binder powder mixtures during SHS process was investigated by combustion-wave arresting technique. Al, Fe, Co, Ni and Cu were selected as binder metals of TiC-based cermet. The characteristics of SHS reaction occurred in different mode, depending on the binder metals. SHS reaction resulted in the three distinct regions; such as unreacted, partially reacted, and fully reacted parts. The intermediate phases of Ti and the metal binder were formed in the partially reacted region. The resulting cermet in the fully reacted region consisted of round shaped carbide particles and metal binder phase.

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WC mono- and multilayer films were deposited on STD61 and cemented carbide substrates by Cathodic Arc Ion Plating process in various bias voltages of 0V to 200V. Chemical compositions and deposition rates were investigated using Energy Dispersive Spectroscopy(EDS) and Scanning Electron Microscopy(SEM). Microstructures of WC films were analysed by X-ray Diffractometer(XRD). The adhesion and microhardness were evaluated by Rockwell-C indentation test method, Scratch test and Microknoop hardness test. The films were formed in a mixture of α-W₂C(hexagonal structure) and β-WC(B1 NaCl structure) phase and the preferential orientation of β-WC have been changed from [311] to [220] with increasing bias voltage. The microhardness of the deposited WC films on cemented carbide were evaluated up to Hk3000 and WC multilayer films exhibited good adhesion in Rockwell-C indentation test and Scratch test.

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Fe-Cr-Al alloys present a great resistance to high temperature oxidation. As well known, Fe-Cr-Al alloys which have been studied for high temperature coating and substrate of catalyst honeycomb have outstanding corrosion resistance at elevated temperature. The isothermal oxidation behaviors of Fe-Cr-Al alloys contains 0.03%Y, 0.05%B, 0.5%Ti, 0.03%Y ＋ 0.5%Ti and 0.5%Zr in dry air at 1,000℃ were examined. The weight gains recorded for Fe-(15, 20)%Cr-(6, 8)%Al specimens progressively increased with oxidation time. The results of XRD for Fe-Cr-Al alloys containing 0.03%Y ＋ 0.5%Ti and 0.5%Zr exhibited excellent oxidation resistance. The oxide of Fe-Cr-Al alloys containing 0.03%Y and 0.05%B exhibited highly convoluted configuration. However, Fe-Cr-Al alloys containing 0.5%Ti, 0.03%Y ＋ 0.5%Ti and 0.5%Zr exhibited noduled configuration. Inward penetration of scale for Fe-(15, 20)%Cr-(6, 8)%Al specimens has been exhibited. For the alloy containing 0.5%Zr, oxidation behavior displayed better isothermal oxidation compared with the Zr-free alloy. And the effects of Zr are to improve the adherence of protective layer of Al₂O₃ scale by pegging effect.

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Duplex austenitic/ferritic stainless steels are known to undergo `475℃ Embrittlement` due to spinodal decomposition in ferrite phase when exposed to temperatures of 300∼550℃. Effects of aging at 475℃ on the corrosion and mechanical properties of Fe-25Cr-7Ni-0.25N-xMo-yW (x = 0∼3, y = 0∼6) alloys were investigated by anodic polarization tests in HCl solution, a modified DL-EPR (double-loop electrochemical potentiodynamic reactivation) test and an impact test. Corrosion resistance of the alloys was degraded with aging at 475℃ owing to depletion of Cr around α` precipitates where numerous micro pits were formed during anodic polarization. Specially for the over-aged alloys, a second anodic current loop appeared in the passive region during anodic polarization in 1M HCl solution. The current value of the second anodic loop as well as the ratio of the maximum current in reactivation loop to that in anodic loop (i_r/i_a) were found to be an effective measure of the precipitation of α` phase during the aging. However, the degradation in corrosion resistance of the alloys during the aging was retarded with an increase in the ratio of wt% W/wt% Mo of the alloys, suggesting that the W in duplex stainless steels delays the precipitation rate of α` phase due to a slower diffusion rate of W compared with that of Mo. Galvanic corrosion behaviors between austenite and ferrite phases for the aged and the unaged alloys were discussed by AFM (atomic force microscopy) observation.

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In order to Investigate the effects of Fe and Mn on the precipitate and corrosion characteristics of Zr based alloys for nuclear fuel cladding, autoclave corrosion tests on the ternary(Zr-0.8Sn-X) alloys have been carried out at 360℃. The corrosion behavior of Zr-Sn-Fe alloy showed the cubic corrosion rate in the pre-transition region and the linear corrosion rate in the post-transition region. The good corrosion resistance in Zr-Sn-Fe alloy system was observed in Fe contents more than 0.2 wt%. The corrosion behavior of Zr-Sn-Mn alloy was significantly accelerated from the early stage. The lowest weight gain was observed in 0.2 wt% Mn. Based on the precipitate anallysis by TEM, it is thought that the corrosion of Zr-alloys would be related to the size of precipitate.

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Sn-3.5Ag (compositions are all in weight percent unless specified otherwise) solder alloys were soldered on the various substrates of bare Cu plate, Cu plate/Ni(2㎛), Cu plate/Ni(4㎛), and bare Ni plate. The morphology, composition and phase identification of the intermetallic compounds(IMC) at the interface were examined using Scanning Electron Microscopy(SEM) and X-ray diffraction(XRD). With varying the Ni layer thickness, various IMCs were formed, which were Cu_6Sn_5 on bare Cu plate, metastable NiSn₃ ＋ Ni₃Sn₄ on Cu plate/Ni(2㎛), Ni₃Sn₄ on Cu plate/Ni(4㎛) and Ni₃Sn ＋ Ni₃Sn₄ on bare Ni plate. And it was also observed that the wetting behavior was dependent on the Ni layer thickness. Such phenomena seemed to be caused by the type of IMCs differently formed on each substrate. As the soldering time was increased, the changes of the IMC morphology and the wetting behavior were observed on the various substrates. Therefore it was postulated that the Ni layer thickness should be considered as an important parameter in the interfacial reaction and the wetting behavior.

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A computer simulation was carried out to investigate the behavior of magnetic field and eddy current properties using FLUX2D on an amorphous choke core. Magnetostatics analysis shows that a flux was gradually increased with forward to inner edge.(No.4→No.10) This is due to the decrease of magnetic path length with forward to inner edge. The existence of gap in magnetic path caused the flux to scatter outside the core. A flux density was lowered inside the core and relatively high on both sides of edge. Two types of the flux density behavior were detected at the gap and 5㎜ above and below from the gap center position, where it had a similar pattern inside the core and extremely different tendency on both sides of edge. Magnetodynamics analysis at the frequency of 30㎑ revealed that eddy currents were concentrated on both sides of edge and near the gap, but almost cancelled out inside the core. The flux density induced by the eddy currents showed almost a similar behavior. This can be interpreted that the eddy currents formed at each shell inside the core were cancelled out each other, while those on both sides of edge and near the gap remain alive.

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