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A study has been made to investigate the superplastic deformation behavior of Ti-6Al-4V alloy based on the theory of inelastic deformation which consists of two mechanisms; the grain matrix deformation and the grain boundary sliding. Load relaxation tests were performed in the temperature ranges from 600℃ to 927℃ to obtain stress-strain rate curves for the samples having 2.5㎛-16㎛ grain sizes. Superplastic deformation tests were also carried out to verify the superplastic deformation behavior. The results showed that grain matrix deformation was dominant at 600℃ and grain boundary sliding became dominant above the temperature of 800℃. The grain matrix deformation behavior was far apart from the power law creep, but found to be rather consistent with the state equation based on the dislocation dynamics. Because of rapid grain coarsening which led to early cavity formation, the tensile elongation became smaller at 900℃ rather than at 800℃.

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The optimum composition of Al-Ni-Ce-Mg alloys forming the amorphous and amorphous plus fcc-Al phase was investigated by the measurement of both hardness, maximum bending strain at fracture(ε_(Bf)), Differential Scanning Calorimetry(DSC) and X-ray diffraction for the as-quenched ribbons produced by melt-spinning. As a results, the alloy ribbon with optimum composition and a mixed phase was Al_(86)Ni_6Ce₄Mg₄. Al_(86)Ni_6Ce₄Mg₄ bulk alloy was produced by extrusion at different temperature of the rapidly solidified powders produced by helium gas atomization. The tensile strength and elongation at room temperature for Al_(86)Ni_6Ce₄Mg₄ bulk alloy extruded at 450℃ were 750MPa and 7.5%, respectively.

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Solderability and interfacial reaction between Cu-substrate and Sn-Bi solder were studied. Experimental variables included Sn contents, types of flux and soldering temperature. Some solder joints are subjected to aging treatments for up to 90 days to see interfacial reaction at 100℃. Analysing the experimental result concerning solderability, it was found that the role of Sn contents is increasing spread area on Cu substrate during soldering. A similar effect is observed by increasing soldering temperature and using activated flux(RMA flux) instead of using non-activated flux(R flux). According to the result of EDXS(Energy Dispersive X-ray Spectrometer), it is supposed that the soldered interfacial zone was composed of Cu₃Sn and Cu_6Sn_6. Those intermetallic compound formed in interfacial zone changed entirely to Cu₃Sn after 5days annealing at 100℃.

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Using TiCl₄ and NH₃ as reactive gases, titanium nitride(TiN) films could be deposited by chemical vapor deposition(CVD) at much lower temperatures(<700℃) than conventionally used ones for TiN deposition. NH₃ gas nitriding method was used to improve the adhesion of TiN film on M2 high speed steel. The nitrides formed on the substrate surface consisted of CrN and ε-Fe_(2-3)N. They had influence on the nucleation and growth mechanism of TiN, which led to more random orientation and coarser columnar grain of TiN films.

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In this paper, the possibility of synthesis and in-situ densification of MoSi₂ alloys using the thermal explosion mode of Self-propagating High-temperature Synthesis was demonstrated. Mo-Si powder mixture synthesized by SHS process under 35MPa yielded porous MoSi₂ product. Proper combinations of the processing variables including the applied pressure, diluent contents, and alloying elements(Al and Ti) yielded the product density up to 99% theoretical density.

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Infiltration behavior of the molten metal and microstructure of the SiC particulate reinforced Al alloy composites which were fabricated by pressureless infiltration technique have been studied. Under the nitrogen atmosphere spontaneous infiltration of the molten Al alloy into the SiC powder bed occurred at lower temperatures as the Mg content of the matrix alloy increased. However, no spontaneous infiltration occurred in the conditions of Mg-containing Al alloy under the argon atmosphere and of pure Al containing no Mg under the nitrogen atmosphere. Thus the presence of both Mg and nitrogen atmosphere must be needed to produce the spontaneous infiltration under the pressureless condition. The primary Si nucleated and grew coarsely on the SiC surface with decreasing cooling rate. It is observed that the reaction products, such as MgAl₂O₄ and Al₄C₃ formed as a result of the interfacial reaction between Al matrix and SiC.

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The creep properties and intergranualr cavitation have been investigated on the Incoloy 800H cold pre-deformed and subsequently crept at 800℃. The material was plastically deformed in tension or compression at room temperature. Creep specimens were machined with the specimen loading axis either transverse or parallel to the direction of cold deformation. The pre-deformed specimens had significantly higher cavity density and showed lower creep rate and lower creep strain than unpredeformed specimens. This effect was observed even after 2% pre-deformation and became more pronounced with increasing the amount of pre-deformation. Metallographic investigations show that cold deformation induces the microcracks, i.e the decohesions at carbide/matrix interfaces, which grow into cavities at elevated temperatures driven by internal tensile stresses which can be reinforced by external loads.

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The present study aims at investgating a spray condition and heat treatment effects on the microstructure and mechanical properties of NiCr coating layer by Diamond-Jet spray system. NiCr self fluxing powders were sprayed on the Cu-Ag substrate under various spray conditions such as distance and grit blasting of substrate, and then heat-treated at temperature range of 500∼1,000℃. Optimum spray condition was evaluated in relation with the mechanical properties and microstructure of the coating layer. In 150㎜ spray distance, the mechanical properties such as adhesive strength, microhardness and wear resistance approved to be excellent, comparing with 250 and 300 ㎜ spray distance is less than that of coating layer in 250㎜ and 300㎜. In grit blasting of the substrate, it was observed that the adhesive strength of coating layer blasted steel grit is superior to that of blasted Al₂O₃ #30 grit. After heat treatment of the NiCr coatings, it was found that the microhardness and wear resistance of the coatings increases with an increase of heat treatment temperature. In particular, the microhardness showed the highest value at 1,000℃. The porosity of the coatings was remarkably decreased with an increase of heat-treatment temperature. Also, diffusion layer(about 20㎛) was observed to be formed at the interface between the coating layer and Cu-Ag substrate at the temperature range of 900∼1,000℃.

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Tundish nozzle blockage during continuous casting of the Al-killed medium carbon steel has been studied. Samples were taken from each sequential step in the processes of ladle furnace down to tundish and their chemical composition were analyzed. Blocked nuzzle were removed from the tundish and cut longitudinally to examine with unaided eye and under an optical microscope. The clogging materials were X-ray diffractometically examined. Safe window was evaluated by thermodynamic data, especially including e^(Ca)_(Ca)=-18, was in good agreement with actual steel samples. In addition, the blockage patterns were investigated from the viewpoint of fluid dynamics. The results are as follows: The ratio of Ca/Al has no thermodynamic significance as regards to conversion of Al₂O₃ into molten Ca-aluminates. The amount of calcium added to prevent nozzle blockage have to set on the basis of Al₂O₃ contents in molten steel. Since excess additions of calcium could form CaS and cause nozzle blockage, the amount of calcium added has to be fine-tuned. Post-mortem investigation of blocked nozzle showed invariably that the CaS accumulated at the bore of sliding plate, which was about the entrance to the diverging section in the nozzle.

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