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The microstructural and mechanical stability of Cu-6 wt.%Ag alloys obtained by cold rolling combined with intermediate heat treatments have been investigated and compared with those of Cu-24wt.%Ag. The stress-strain responses and fracture behavior of Cu-6 wt.%Ag alloys were examined and correlated with the microstructual change caused by thermo-mechanical treatments. The linear white markings are thought to be deformation bands stabilized by silver atoms, not silver filaments as eutectic Cu-Ag alloy. The highly deformed microstructure stabilized by silver filament is unstable at temperatures above 300℃ because of the increase of the diffusivity of silver atoms. The strength of Cu-6 wt.%Ag alloys were found to be decreased remarkably if they were heat-treated above 300℃ for 1hr. The fracture surfaces of Cu-6 wt.%Ag alloys showed topical ductile type fracture. The electrical conductivity did not change appreciably up to the aging temperature of 200℃ and increased rapidly at temperatures above 300℃. The increase of the conductivity and the decrease of the strength can be associated with the coarsening and spheroidization of highly deformed linear band structure. The strengthening mechanism and microstructural stability were discussed based on the microstructural analyses.

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Morphological evolution and growth mechanism of MC carbide during solidification were investigated in a Ni-base superalloy Mar-M247LC by the directional solidification and quenching(DSQ) technique at various growth rates(0.5∼100×10^(-6)㎧). As increasing the growth rate, carbide morphology transformed from equilibrium octahedron shape to complex blocky, script, and spotty shapes. The conditions of solidification variables [rate(R) and thermal gradient(G)] to farm various shapes of the MC carbide were identified by the DSQ experiment. It was found that the carbide size decreased with increasing solidification rate and thermal gradient. The solidification criteria to form various carbide sizes applied to equiaxed castings. The solidification variables, G and R, were also estimated by the commercial casting simulation software, ProCAST, at different sections of an equiaxed modelling bar casting. Distribution of various MC carbide size could be predicted in the castings.

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A mechanical spectroscopy study has been made on fine-grained Ni-TZP(ZrO₂-3 ㏖.%Y₂O₃) composite in an attempt to assess the following micromechanical prediction. A dual-phase material with fine-grained constituents deforming by Coble-type boundary-diffusion creep exhibits viscoelastic (anelastic plus viscous) behavior. A composite with 10 vol.%TZP, fabricated by powder processing is examined. Dynamic Young`s modules, E_ω and internal friction, tan Φ, are measured over a temperature range of 25 to 800℃ at frequencies of 0.01, 0,05 and 0.1 Hz using a specially designed tension-compression apparatus. The data obtained are analyzed in terms of loss compliance, J₂◎ tanΦ/E_ω. Two relaxation peaks are observed in the composite. An exponential involved in the peak and background components are determined and, by making a further analysis based on the micromechanical formulation and also taking the well-known relaxation due to viscous grain-boundary sliding into account, the implications of these quantities are discussed in terms of constituent material parameters(boundary diffusivity, grain size. etc.).

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A study has been made to establish an optimum condition in the surface treatment that is important for the fabrication of hybrid composite material,(ARALL: Aramid Aluminum Laminates, CARALL: Carbon fiber Reinforced Aluminum Laminates) and their mechanical characteristics were investigated. PAA(Phosphoric Acid Anodizing) provided good adhesive strength. On the other hand, the poor adhesive strength was shown on vapor degrease, CAA(Chromic Acid Anodizing) and FPL(Sulfuric/Sodium Dichromate Acid Etching) was nearly PAA. In case of fiber direction of 0 degree, the tensile strength of CARALL hybrid composite was increased with increasing fiber thickness, e.g., the tensile strength of 8 ply carbon laminate CARALL was 233% higher than that of Al 7075-T6 sheet. However on fiber directions of 45 degree and 90 degree, the tensile strengths of CARALL were decreased compared with that of 0 degree. By the FEM analysis, it was found that a partial stress increases in order of epoxy adhesive, aluminum, CFRP(Carbon Fiber Reinforced Plastics). The CARALL nearly satisfied the law of mixture despite of the fiber direction and thickness. The impact resistance of CARALL was higher than that of CFRP.

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The high temperature deformation behavior of 15 vol.% SiC_p/Al6061 composites has been studied in the temperature range of 300-550℃ and in the strain rate range of 0.1-3.0/sec by employing the concept of deformation efficiency from the stress-strain data as a function of temperature(T) and strain rate(ε˙). The strain rate sensitivity(m) of the composites is evaluated and calculated the deformation efficiency(η)[η= 2ｍ/(ｍ+1)] to obtain deformation maps, which were obtained from the values of deformation efficiency. The composite reinforced with 8㎛ SiC_p exhibited a domain of dynamic recrystallization(DRX) with a peak efficiency of 40% at the temperature range of 450∼500℃ and the strain rate range of 0.2∼0.5/sec. On the other hand, the composite reinforced with 1 ㎛ SiC_p showed the DRX domain, which was moved to lower temperature of 370-430℃. These materials undergo microstructural instabilities at -370℃ under the high strain rates of 1.0 and 3.0/sec as predicted by the continuum instability criterion. The characteristic of these results has been investigated with the help of microstructural observation.

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The high purity Si powder was prepared by Self-propagating High-temperature Synthesis(SHS) Process from a mixture of SiO₂and Mg as raw materials. The effect of the processing parameters on the characteristics of the product such as molar ratio, particle size, compaction pressure and leaching conditions were studied. In the case of 20∼60 mesh of Mg particle size, the complete reduction of SiO₂ required excess magnesium, 2.6 mole, whereas unreacted SiO₂was completely eliminated with stoichiometric molar ratio, 2.0 mole of 140∼200 mesh Mg powder. As the Mg particle size was decreased, the combustion temperature increased and the particle size of the product decreased. The concurrently formed MgO in the product was leached with an diluted HCl solution at 70℃ for 3 hours. The product silicon had a purity of 99.88% which was higher than that of the reactant SiO₂. This is because the impurities were either volatilized at the high temperature generated during the rapid exothermic reaction or dissolved into the HCl solution during leaching.

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Al₂O₃-WC composite powders were synthesized by Self propagating High-temperature Synthesis (SHS) using Al powders as reducing agent. WC, W₂C, and Al₂O₃ were concurrently formed in WO₃-Al-C system. Thermodynamical data for the system was applied to study on the phase selection. It was found that the complete reaction was achieved with excessive addition of carbon and appropriate processing parameters such as degree of dilution, particle size of aluminum, pellet compaction pressure and amount of carbon source. The final product which was leached by 10% 1 : 4 HNO₃+ HF diluted solution consisted of Al₂O₃-55 wt%WC having 2∼3 ㎛ of mean particle size.

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Reactive ion etching(RIE) characteristics of TiN film coated on a cemented carbide was studied with CF₄/O₂ mixture. The etching rates of the film were measured as a function of gas mixture ratio, RF power, substrate temperature, and pressure. The etching rate was increased with the increase of O₂ gas concentration and reached a maximum value at about 20% of O₂ and above which the rate was decreased. The etching rates were increased with the RF power, the pressure, and the substrate temperature. The Arrhenius plot of the etch rates versus the reverse substrate temperature shows activation energies of 5.0 ㎉/㏖ and 4.2 ㎉/㏖ for CF₄/20% O₂ and CF₄, respectively. The chemical composition of the etched surface was analyzed by X-ray photoelectron spectroscopy(XPS). Fluorine atoms were detected in the base material because it diffused into the substrate in CF₄/20% O₂plasma. Atomic force micro-roughness measurement showed a smooth surface when it was etched with CF₄, but the roughness was increased by adding 20% O₂. The cuttability was not degraded by the re-deposition of TiN film on the cemented carbide after the etching process.

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The physical soundness, microhardness and wear properties of the thermally sprayed TiC-Fe wear-resistant coatings have been investigated. Thermally sprayed coatings were fabricated by HVOF and the subsequent heat-treatments were carried out at temperatures ranging from 800℃ to 1000℃ in either vacuum or air for 30 minutes. The wear resistance of the as-sprayed TiC-Fe alloy coatings was found to be better than that of Cr₃C₂-NiCr alloy coatings and similar to that of WC-Co coatings. In addition, the wear resistance and hardness of the coating were improved by the following heat-treatment in vacuum(∼10^(-3)torr). The maximum improvement in wear resistance and microhardness was about 20 and 30%, respectively by the heat-treatment performed at 900℃ in vacuum, while the heat-treatment in air deteriorated the wear property due to oxidation. It has been revealed, from TEM and Mo¨ssbauer studies, that the improved wear resistance in the heat treated coating was mainly caused by the hardness increase associated with martensitic transformation. However, no improvement in the wear resistance of the TiC-Fe coatings heat-treated in air seemed to be caused by the residual stress due to the oxidation of Fe matrix.

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The micro-pulse d.c. plasma system has been adopted to the paste boriding of steel to reduce the optimum process temperature. By using pulsed plasma, the most desirable microstructure and hardness are obtained at 700℃ which is about 100℃∼200℃ lower than that of typical gas boriding. The X-ray diffraction analysis shows that the tooth-shaped dendrite in the surface layer is mainly the mixture of FeB and Fe₂B. The composition of paste which determines the chemical potential of dissolved boron greatly influences the optimum process temperature and mechanical properties of boride layer.

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