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Formation of macrosegregation in squeeze casting of an Al-7wt%Si alloy was investigated with regard to microstructural evolution under various process variables. The effects on the macrosegregation area of the process variables, such as applied pressure, pouring temperature, die temperature, delay time before pressurization, and height/diameter ratio of the casting were investigated. As the applied pressure increased, the macrosegregation area increased while the length of columnar grains decreased. However, as the die and the pouring temperatures increased, both the macrosegregation area and the length of columnar grains increased. The increase in the delay time for pressurization after pouring also resulted in the increase both of the length of columnar grains and the macrosegregation area. It was found that the macrosegregation area decreases with increasing the amount of equiaxed grains in castings.

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Thermal deformation of slab mold during continuous casting was analysed by the coupled finite element method with heat and thermo-elasto-plastic deformation. In order to consider the effect of air gap on the heat transfer coefficient between strand and mold, thermal deformation of strand and temperature distributions in strand and mold were calculated. The effects of mold thickness, temperature of cooling water, velocity of cooling water and mold taper on deformation of mold was investigated. The deformation of mold was due to the difference of thermal expansion between mold and supporting plate of mold. During heating in continuous casting process, mold was deformed toward the strand, while mold was deformed toward the supporting plate of mold during cooling. The amount of deformation increased with increasing the hot face temperature in mold.

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A metal matrix composite is, nowadays, considered as a favorable material due to merits in mechanical properties, such as in comparison with a gental metal material. But at the same time, its fault has been considered to deteriorate a strength of composite by heating residual stress of the matrix. Therefore, it is necessary to remove a tensile residual stress, to produce the strength of a composite better. On the contrary, if compressive residual stress happens in matrix of composite in place of tensile residual stress, it`ll make the strength of composite better. So that, this paper introduce the development of a high strength of composite, by using compressive residual stress well, on the study. The compressive residual stress in matrix of a composite may be produced by using TiNi alloy of shape memory alloy (SMA), which can lately occurs a volume fracion, according to a phase transformation, before searching for the effect on the improvement and also confirms its intelligent properties. Finally, we point out the possibility of the speciality of a shape memory composite as an intelligent composite.

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The main objective of this study is to investigate the effect of microstructure on the fracture behavior in two Al-Ni composite piston rings fabricated by squeeze casting method. Microstructural observation and insitu SEM fracture test were conducted on the composites to identify the microfracture processes. Detailed microstructural analyses showed that the reinforcing Ni contained an amount of Ni₃Al and NiAl phases near the Ni/Al interfacial region, which enhance the overall hardness of the composites. It was also found from in-situ observations of crack initiation and propagation that the interfacial debonding occurred at the Ni/Al interface in the early loading stage, providing an easy crack propagation path. In order to improve mechanical properties of the composite piston rings, thus, the improvement of interfacial properties by applying a new coating method is suggested.

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The knowledge of microstructures, hence properties can be found from an understanding of phase equilibria. Such an approach has been adopted in the present study to design Al-Al₃(Ti, V, Zr) composite system. Phase stabilities of multicomponent trialuminides are explored first by experiments at various temperatures and then thermodynamically optimized for the purpose of dispersing them in the rather soft aluminium matrix and eventually making composites. Using these obtained thermodynamic parameters, quasi-ternary Ti-V-Zr sections of Al-2at%(Ti, V, Zr) and Al-6at%(Ti, V, Zr) composite systems were calculated at 698K. At 698K, where aluminium alloys are put into service for high temperature use, phase diagrams, overall lattice misfits, volume fractions and coarsening rate constants were calculated. Based on these calculations, optimum alloy compositions which were supposed to maximize the strengthening effects at high temperatures were suggested.

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TiNi intermetallic compounds were manufactured by using the self-propagating high-temperature synthesis process. The effects of chemical compositions(Ni/Ti=0.5∼2.0 molar ratio), compaction pressure and preheating temperature on the reaction were investigated. As the molar ratio of Ni, compact pressure and preheating temperature increased, the combustion temperature and velocity increased. Also it was found that the secondary and third phase were appeared as well as main TiNi phase under the non-preheating. At the same condition, the production with preheating of 200℃ was only found the TiNi single phase by perfect reaction. Hence, the reason of the different phase formation at the reaction stages with various factor was discussed and the schematic diagram of the synthesis process was proposed in this paper.

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83Zr-17Ni alloy coatings on Monel 400 substrate were produced by the hot dipping. The coating layer of 30 ㎛ thickness was obtained at 1050℃ for 1 min. dipping. The formation of Zr₂Cu was found at the substrate/coating interface during the hot dipping. The selective oxidation during the heat treatment led to the formation of Zr-rich oxide on the coating layer containing Zr. It was found that the coating layer was consisted of an outer ZrO₂ layer and an inner oxide/metal composite layer with a conversion heat treatment at 1030℃ for 20hr. These oxide and composite layers resulted in an increase on the hardness. The oxidation rate was decreased with hot dipping and also with conversion. It was proved that the resistance to spallation was enhanced by coating.

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The oxidation behaviors of Fe₃Al+2.13Cr, Fe₃Al-0.04B+2.0Cr, Fe₃Al+0.04B+4.68Cr(at.%) alloys were studied in 1 atm of air at 800, 1000 and 1200℃. All the alloys tested exhibited excellent oxidation resistance in both isothermal and cyclic tests at 800℃. In isothermal tests, Fe₃Al+4.68Cr+0.04B alloy exhibited the best oxidation resistance regardless of the testing temperatures. In cyclic tests, this alloy also showed superior oxidation resistance below 1000℃, though less-resistant at 1200℃. At 1200℃, all the alloys showed severe spallations, the amount of which being increasing in the order of Fe₃Al+2.13Cr, Fe₃Al+4.68Cr-0.04B and Fe₃Al+2.0Cr+0.04B. Generally, the effect of B was found to increase the isothermal-oxidation resistance but found to decrease the cyclic-oxidation resistance. The beneficial effect of Cr on the improvment of both isothermal and cyclic oxidation resistances was observed.

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The oxidation behaviors of Fe₃Al+2.0Cr+0.04B and Fe₃Al+1.87Cr+0.04B+0.14Zr(at.%) alloys were studied in 1 atm of air at 800, 1000 and 1200℃. Though the isothermal oxidation behavior of these alloys was relatively similar, the Zr-added alloy displayed better cyclic oxidation behavior with negligible scale spallations compared with the Zr-free alloy, especially at temperatures above 1000℃. The effects of Zr are (i) to improve the adherence of protective layer of Al₂O₃ scale by mechanically keying the scale, (ii) to facilitate the rapid formation of the scale by providing heterogeneous nucleation sites, (iii) to act as a vacancy sink by vacancy accomodation and (iv) to relieve the growth stress by decreasing Al^(3-) counter diffusion and by preventing the formation of new oxides within the pre-existing oxide.

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Formation of (Bi_(0. 25)Sb_(0. 75))₂Te₃ alloy was completed by mechanical alloying of the as-mixed Bi, Sb, and Te granules of ∼5 ㎜ size for 5 hours at ball-to-material ration of 5:1. When hot pressed at temperatures ranged from 300℃ to 550℃ for 30 minutes, figure of merit of (Bi_(0. 25)Sb_(0. 75))₂Te₃ increased with increasing hot pressing temperature and maximum value of 2.8×10^(-3)/K could be obtained by hot pressing at 550℃. When hot pressed at 400℃, figure of merit was increased from 2.0×10^(-3)/K to 2.37×10^(-3)/K with addition of 1.25 wt% Sb as an acceptor dopant. With further addition of Sb, however, figure of merit was abruptly decreased. When hot pressed at 550℃, figure of merit(∼2.8×10^(-3)/K) was little changed with addition of Sb up to 2 wt%, and then decreased abruptly below 0.5×10^(-3)/K with further addition of Sb.

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