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The microstructural stability of Cu-Nb filamentary microcomposites wires fabricated by the bundling process were examined using TEM(Transmission Electron Microscope). The cross sectional shape of most Nb filaments in bundled wires appear straight with slight curvature. Nb filaments were distributed rather randomly and extremely irregular or heavily kinked Nb filaments were distributed to the cylinderization of Nb filaments during bundling process at high temperature. No flaws were observed near interface regions between subelemental wires and copper sheath, suggesting excellent bonding was promoted by copper sheath. Nb atoms were dissolved and numerous Nb precipitate were found to be formed in copper channels during bundling process. Twins were occasionally observed to have a twin relationship, indicating Nb filaments are strong barriers to twin propagation.

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The effect of the processing factors of self-propagating high temperature synthesis(SHS) was studied on the system of TiO₂/Al/C. The effect of the size of green pellet and initial temperature of reactant on the combustion temperature cooling time and grain size were studied. The prepared Al₂O₃-TiC powders under various cooling time were sintered by pressureless-sintering and hot-pressing to compare their properties. The properties of commercial powder and powder synthesized by SHS were compared each properties. The cooling time can change by the preheating and the size of pellet. The cooling time affected largely grain size cf titanium carbide. However, the grain size of alumina was nor affected by cooling time. The cooling time after complete combustion have to maintain during for a long time. The Al₂O₃-TiC composite of powder prepared by SHS had good properties comparable to commercial powder.

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In this study, Al-Ni-Mm (Mm=misch metal) alloy has been fabricated by a high pressure gas atomization technique and consolidated by a powder extrusion method. The gas atomized powders showed mixed structures of amorphous matrix, fcc-Al phases and intermetallics particles. Each phase shows different size and quantity with different size of the powders due to the higher cooling rate of the finer atomized powders. Because of the difference of the microstructure, the powders with the different size show differences of the mechanical properties of the atomized powders and extrudates. That is, because of the fine microstructure the extrudate from the fine powders shows higher strength and elongation than that from the coarse powders. The white bands which are appeared in the extrudates are examined, and the origin is analyzed.

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A bulky Al_(84)Ni_(9.5)Mm_(6.5) alloy has been produced by a high pressure gas atomization and warm compaction technique of the gas atomized powders smaller than 25㎛ in diameter, which has nanocrystalline Al particles embedded in amorphous matrix, at various compaction temperatures. The hardness, density, elongation and strength of the compacts have been examined and compared with the properties of heat treated specimens of melt spun ribbon with the same chemical Composition. The mechanical properties of the compacts are affected by the combined effects of the mechanical properties of the material itself, the porosity of the compacts and the bonding state between the powders. The hardness of the compacts is explained using the plasticity theory of porous materials.

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In an attempt to lower the ignition temperature of the combustion synthesis of MoSi₂, the synthesis was conducted using elemental Mo and Si powder mixtures prepared by mechanical alloying. The mechanical alloying resulted in powders with microstructure of alternating layers of Mo and Si phases. The ignition temperature of the combustion synthesis for the mechanically alloyed powders was measured to be around 670℃, which is almost 550℃ lower than that for the powder mixture prepared by low energy ball milling. A mathematical model is developed to explain the decrease in ignition temperature for the powders prepared by mechanical alloying. Based on the mathematical model, the effects of mechanical alloying time on the ignition temperature as well as the combustion behavior are discussed.

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The effect of Mn alloying on the growth rate and oxidation resistance of MoSi2 coatings formed by pack siliconizing process, (Mo-Mn)Si₂ coatings formed by single-step pack process (codeposition of Si and Mn), and two-step pack process (manganizing+siliconizing), respectively, was investigated at 1373K and 1573K. The growth rate of MoSi₂ coatings was fast in order of two-step pack process, single-step pack process and pack siliconizing process at 1373K because the increase of Mn concentration on MoSi₂ coating surface resulted in the increase of mass balance condition of silicon for MoSi₂ growth. The static and cyclic oxidation resistance decreased in order of two-step pack process, single-step pack process, and pack siliconizing process in air at 1573K because higher levels of Mn tended to retard the growth rate of Mo_5Si₃ diffusion layer and rapid oxidation at the edge of MoSi₂ coatings was prevented by the formation of thick Mn-Si-O complex oxides and decrease of the formation frequency of microcracks within MoSi₂ coatings.

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The surface of Al-Si 12% alloys has been modified by laser surface melting process. A 5 kW CO₂ laser has been used to melt the surface of casting alloy. The dimension and microhardness of molten zone have been investigated for mono- and multi-pass. The dimension of molten zone depends on the parameters (power, scanning velocity......) of laser beam. The microhardness increases as the crystalline size and interdendritic space decrease and the scanning velocity increases. A substantial reduction of silicon particle size has been achieved from about 50 microns before laser melting to about 1 micron after laser melting with scanning velocity of 1 m/min. The relationship between solidification rate and scanning velocity has been also studied. The solidification rate begins to zero at the interface between substrate and molten zone, and rapidly increases up to a value equivalent to the scanning velocity at the surface. Interdendritic space depends on the quenching rate. It decreases with the speed of treatment and it is about 1 micron with a scanning velocity of 10 m/min.

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TiN coatings were deposited on M2 high speed steel by the plasma enhanced chemical vapor deposition(PECVD) process using a gas mixture of TiCl₄, NH₃, H₂ and Ar with various NH₃/TiCl₄ flow rate ratios(Q(NH₃)/Q(TiCl₄)), and the effect of the flow rate ratio on the color, structure and property of TiN coatings has been investigated. Structural and compositional analyses were conducted by X-ray diffraction method(XRD), transmission electron microscopy(TEM), Rutherford backscattering spectroscopy(RBS), as well as Auger electron spectroscopy(AES). At low flow rate ratios, bright gold coatings with high hardness and low resistivity could be formed. At higher ratios, on the other hand, coatings of brown color were formed. They showed porous microstructures with considerably decreased microhardness. Results from structural and compositional analyses showed that a large amount of oxygen had been substitutionally incorporated in the brown color TiN during the deposition process to form titanium oxynitride. It has been found, however, that the color change of TiN coatings is closely related with the surface roughness of the coating rather than with the presence of oxygen in the coating.

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The present study is concerned with the fabrication and the microstructural analysis of a TiB₂/Ti surfacealloyed material fabricated by high-energy electron beam irradiation. The mixture of TiB₂ powders and flux was deposited on a Ti-10V-2Fe-3Al alloy substrate, and then electron beam was irradiated on these mixture using an electron beam accelerator. The melted region of about 1.5 ㎜ thickness was homogeneously formed without pores or cracks, and was composed of primary and eutectic TiB borides in the β phase matrix. The formation of these TiB borides greatly improved hardness, especially high-temperature hardness up to 450℃. These findings suggested that the surface-alloying method using high-energy electron beam irradiation was economical and useful to the development of new advanced materials with improved high-temperature properties.

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The effects of Zr addition and heat treatment on the corrosion properties of the squeeze cast Mg-5wt%Al alloy have been investigated by potentiodynamic polarization test, impedance measurement and immersion test in deaerated 3.5wt%NaCl solution. Mg-5wt%A1-0.6wt%Zr alloy was solution heat-treated at 415℃ for 24hrs and then artificially aged at 220℃ for 55hrs (T6). The results show that the Zr addition in the squeeze cast Mg-5wt%Al alloy increases the corrosion resistance mainly due to the grain refinement and uniform distribution of Mg_(17)Al_(12) phases. Heat treatment affects greatly the microstructures and corrosion properties of Mg-5wt%Al-0.6wt%Zr alloy. The corrosion resistance of Mg-5wt%Al-0.6wt%Zr alloy decreases in the order, T6, as-cast, solution heat-treated condition. The superior corrosion resistance in T6 heat-treated condition is considered to be due to the effective pit propagation barrier behavior of Mg_(17)Al_(12) discontinuous precipitates.

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