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The quantitative analysis of hydrogen content together with the observation of the morphological changes in the microstructures of Al-4.5wt%Cu alloy induced by electromagnetic stirring was carried out. Hydrogen content was measured in two states. In the liquid state above the liquidus line hydrogen content was increased with increasing melt temperature and isothermal holding time. In semi-solid state using electromagnetic stirring hydrogen content was measured by high vacuum extraction method, according to the conditions of stirring such as cooling rate, input voltage and solid fraction. As the cooling rate was increased under the influence of stirring, the amount of hydrogen gas was increased. It is resulted from the fact that the diffusion of hydrogen due to the difference of hydrogen solubility between in liquid state and in semi-solid state is different with cooling rate. As input voltage was increased, hydrogen content was slightly decreased. This result was different from that of conventional cast, and it is explained in terms of the change of microstructures induced by electromagnetic stirring. However, hydrogen content with the solid fraction was not changed significantly. From above the results, it is also shown that both the changes of the microstructure and hydrogen content by electromagnetic stirring have influence on the type of porosity.

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14㎝ length Al-15Cu-1Mg alloys in 3㎜ I.D. alumina tubes have been directionally solidified under the furnace temperature of 760℃. Furnace moving velocity(V) was changed with the range 0-120㎝/hr. By analysing the evolution of the temperatures profiles along the specimen length, the growth characteristics-the position of the solid/liquid interface, temperature gradient(G) and local growth velocity(R)-have been examined. The microstructures of the alloys have been observed for the investigation of microstructural uniformity along the specimen length and the effects of the furnace moving velocity(V).

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Reinforcement of shape memory alloys within metal matrix reveals compressive residual stresses in the matrices resulting in improved tensile properties of the composites. In the present study, Al/TiNi shape memory composites were fabricated by the squeeze casting technique. Optimal fabrication conditions for squeeze casting were obtained experimentally. Fairly good microstructure and matrix/reinforcement bonding observed in the squeeze cast Al/TiMi composites. Tensile tests of the composites were carried out above Ar(austenite finish temperature) which was found from DSC analysis. The amount of prestrain to induce the compressive residual stress in Al matrix and the recovery force of the TiNi were determined from tensile curves of TiNi wire. Improved strength of the composite due to TiNi reinforcement as well as compressive residual stresses in Al matrix was identified. It was found that the total interfacial area between matrix and reinforcement which depends on the wire diameter also affected the strength enhancement.

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Mechanically alloyed (MA) oxide-dispersion-strengthened(ODS) Ni-based superalloy attract great attention as advanced high temperature materials, because they can retain useful strength up to a relatively high fractions of their melting points. Production of a coarse elongated grain structure is very important in MA ODS alloys, since the creep rupture strength is usually increasing with the increasing grain aspect ratio(GAR). The formation of coarse elongated grains is possible during secondary recrystallization by a process of directional zone annealing. The effects of the primary grain sizes on the GAR values of a newly developed MA ODS Ni-Based superalloy, alloy 99, were investigated. The grain structure after zone annealing was strongly depended on primary grain size of as-extruded this alloy. The optimum grain sizes for production a coarse elongated structure ranged from 0.45㎛ to 0.55㎛ in this alloy system. When the primary grain size was less than 0.4㎛, preannealing heat treatment prior to zone annealing brought into the optimum grain size, thereby producing a coarse elongated structure.

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Damping properties of Al/NiTi sintered materials were studied. The mixtures of elemental powders(Ni-48.5-51.5at.% Ti) were mechanically alloyed(MA) by high energy ball mill. During the MA for 10 hours, amorphization and particles refinement were formed. MA powders of amorphous phase were crystallized to martensite(B19` ) and austenite(B2) after heat treating for 1 hour at the temperature of 850℃. Heat treated powders were mixtured with aluminum powders by ball milling, and swaged at room temperature and hot rolled at 450℃. Damping properties of Al/NiTi sintered materials measured with cantilever beam method. The damping capacity of Al-20vol% NiTi was increased with Ti amount of NiTi intermetallic compounds and was related with the amounts of B19′. No effect of interphase on the damping properties was obtained.

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Phase transformation behaviours and high temperature mechanical properties of Mo and Co alloy coating layers made by plasma spray coating method have been investigated by means of optical microscopy, X-ray diffraction, high temperature microvickers hardness and wear tests. The splat is relatively flat with the boundary in Mo coating layers, whereas wavy in Co alloy coating layers at high temperature. Crystallization of Co alloy coating layers which were amorphous at room temperature started to occur at about 1073 K and consequently Co_7Mo_6 and Co₃Ma compounds were formed. Wear volume of Co alloy coating layers almost kept constant with increasing temperature below 1073 K, and then started to increase at 1073 K. This was attributed to the crystallization which resulted in decrease in hardness- Wear resistance of Co alloy coating layers was superior to that of Mo coating layer overall test temperatures.

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The magnetostrictive and magnetic properties of the melt-spun ribbons of (Tb_(0 33)Fe_(0 67))_(1-x)B_x (x=0, 0.02, 0.05, 0.10 and 0.15) alloys are investigated as a function of the surface velocity of the wheel during melt-quenching, The low field sensitivity of magnetostriction is found to be improved substantially by the addition of B. The saturation magnetostrictioin, however, decreases continuously with increasing B content; for example, the magnetostriction at an applied magnetic field of 8 kOe decreases from 1300 ppm (x=0) to 630 ppm (x=0.15) when the ribbons quenched at an optimum condition are considered. Good low field sensitivity of magnetostriction combined with large magnetostriction is obtained for the ribbons with a nanocrystalline grain structure which is achieved in this work even in the as-spun state. The magnetostrictive and magnetic properties are significantly affected by the formation of an amorphous phase; the saturation magnetostriction and magnetization are reduced but the magnetic softness (the low field sensitivity of magnetostriction and coercive force) is improved. The present results are discussed in terms of the variation of the grain refinement/amorphization with the surface velocity and the B content, and the change of intrinsic magnetic properties with the B addition.

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Interdiffusion and intermetallic compound formation between Ni thin film and molten In have been investigated in flip chip bonding process. In films were deposited on the BLM (Au/Ni/Ti)/Si substrates by thermal evaporation. Heat treatments were performed in the RTA (Rapid Thermal Annealing) system and/or in a furnace. Intermetallic compound formation was charactered by XRD. Ni_(10)In_(27) and Ni₂In₃, phase are formed at the interface between In and Ni. Ni_(10)In_(27) is observed in all specimens after heat treatment, but the formation of Ni₂In₃, phase depends on the thermal treatment conditions. The thicker intermetallic compound Layers were formed when the specimens were heat treated in the furnace. The formation and the thickness of intermetallic compounds were related to the kinetics of In solder reaction and interdiffusion.

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In this study particle flow in a shaft-typed furnace was analysed using a 2-dimensional scale mocel. The measured trajectories of burden turned out to be well matched with the calculated one. On lump-only charging, the discharging characteristics of particles at the lower part of the furnace based on the kinematic model, illustrated the "W" type which resulted from the descending speed differences between the middle and wall or center zones. On pellet-lump misting, material and particle segregations by friction always occurred, resulting in "inverted U" shaped discharging profile due to faster descending at wall.

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The deformation behavior of commercial austenitic stainless steels under hot rolling conditions was investigated by means of hot compression tests performed in the temperature range 900℃ to 1200℃. Based on the variation of dislocation density due to strain hardening and dynamic recovery during hot deformation, the high temperature flow stress was formulated as a function of strain and steady-state flow stress by employing a modified Laasraoui-Jonas` model. The strain rate and temperature dependence of the steady-state flow stress was analyzed by using Sellars-Tegart`s model. The resultant constitutive equation, which correlates the flow stress with strain rate, temperature and strain, fitted well with the measured stress-strain curves. Type 304N1 steel exhibited a lower dynamic recovery rate than Type 304 and 316L steels, which was attributed to the enhancec planar slip due to nitrogen addition. The temperature dependency of steady-state flow stress was found to increase in the order : Type 304, 316L, 304N1.

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