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Al-Cr-Zr nanocrystalline alloys were prepared by mechanical alloying and hot extrusion. High temperature mechanical properties and microstructural characteristics of Al-Cr-Zr alloys were investigated in order to evaluate their high temperature applications. The tensile strengths of MA Al-Cr-Zr alloys were substantially higher than those of conventional 7075 aluminum alloy and RSF Al-Fe-Si alloy at temperatures above 150℃. The strain rate sensitivities and flow stress of MA Al-Cr-Zr alloys were increased with higher strain rate, but decreased with increasing testing temperature. The lowest value of strain rate sensitivity of the alloy obtained in the present study was 0.014 at 400℃. The tendency of ductility decrease at higher temperatures could be explained the pull-out mechanism of dispersoids such as Al₃Zr and Al_(13)Cr₂ and the plastic instability resulting from enhanced dynamic recovery.

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Molybdeum disulfide (MoS₂) is widely used as a solid lubricant material for space and bearing applications. In this study, deposition of MoS₂-Ti composite thin films by D.C. magnetron sputtering was investigated to reduce rapid oxidation and the micro-structural change of MoS₂ film. The addition of Ti interlayer significantly extended the film`s wear life in proportion to increasing thickness of Ti. In the deposition of MoS₂-Ti thin film, the film showed best wear resistance when Ti content was in the range of 5-10 wt%. Codeposited Ti functioned as an oxygen getter to form TiO₂. When the Ti content in the composite film exceeded 10%, the interference of Ti in MoS₂ gliding mechanism decreased the film`s wear life.

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Brasses are the most widely used copper-based alloys because of the good corrosion resistance and formability. The leaching of lead to potable water could produce serious medical problems. Due to the leads toxicity, nontoxic bismuth is the most alternative to lead for the machinability of brass. Effect of Bi on dezincification of unleaded brass was evaluated in synthetic tap water. Potentiodynamic, potentiostatic tests, open-circuit potential measurements, SEM, and EPMA analyses were used to investigate the corrosion characteristics of Bi-containing brasses. The leaded brass had only a slight tendency to dezincification, whereas the Bi-containing unleaded brasses were more susceptible. As the content of Bi increased, the corrosion resistance of unleaded brasses increased due to the decreased amount of βphase.

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Three kinds of L1₂-type Al₃Ti-Cr alloys, i.e., Al_(67)Ti_(25)Cr_8, Al_(66)Ti_(24)Cr_(10) and Al_(59)Ti_(26)Cr_(15), were prepared by induction melting and homogenization followed by thermomechanical treatment. The cyclic oxidation behavior of these alloys was investigated at 1100, 1200 and 1300℃ in air. The prepared alloys showed excellent oxidation resistance at the temperature range of 1100∼1300℃, with slightly different oxidation behavior. The cyclic oxidation resistance decreased in the order of Al_(59)Ti_(26)Cr_(15), Al_(66)Ti_(24)Cr_(10) and Al_(67)Ti_(25)Cr_8. As the content of Al increased, scale spallation increased, leading to the decreased cyclic oxidation resistance. The oxide scale was primarily composed of α-Al₂O₃, which was contaminated with Cr₂O₃ and TiO₂.

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A die internal corner gap is usually found during equal channel angular pressing(ECAP) of materials. The die corner gap as well as the channel angle determines the strain generated during ECAP. Finite element analysis using the DEFORM2D code is carried out in order to investigate the corner gap formation between the die and workpiece during the plane strain ECAP process. The comparison of the deformation and the corner gap formation behaviour between the strain hardening materials and the quasi-perfect materials was made. The mechanism of the corner gap formation is described in conjunction with the strain hardening behaviour and flow velocity of the workpiece in the deforming zone. The adjustment of the corner angle from the die corner angle to the workpiece is necessary for a better prediction of the strain during ECAP.

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Residual stresses present in diamond films produced by the CVD process often cause cracking and bowing of films, and then degrade product quality. To discuss the causes of bowing and cracking, the measurement and mechanical analyses of residual stresses are very important in diamond film research. Of the residual stresses, the intrinsic stress is one of the most important research topics because its effect on bowing of a free standing diamond film is strong even for its small magnitude. Quantification of the intrinsic stress is limited because high-temperature plastic deformation of Si substrate enlarges the substrate bending. In this study, an analytical model is proposed to obtain the initial intrinsic stress without contribution of the plastic deformation of the substrate. This new model in which the plastic deformation of Si is considered was developed using elastoplastic beam theory and diamond etching technology. In the model, the plastic deformation of Si is given by plastic curvature of substrate measured after removing the diamond film. The experiment is performed on diamond films deposited by microwave plasma assisted CVD. The results show that the overestimated intrinsic stress can be compensated successfully through the new model, which is consistent with that by Raman spectroscopy. The effects of film thickness and deposition temperature on residual stress is discussed in terms of microstructural change of diamond film.

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To obtain the thermodynamic properties of a multicomponent liquid alloy system over the whole range of concentration at an arbitrary temperature, the free volume theory has been applied to derive the formula of activity coefficients of liquid solutions based on the infinitely dilute solutions. The Monte-Carlo algorithm was used to calculate the nonlinear end value equations of binary systems, and the free volume parameters obtained were directly correlated with the activity coefficients of liquid binary, ternary and quaternary at an arbitrary temperature. The activities of Pb-Sn alloy system calculated by this method were verified in good agreement with the experimental values from the literature, and the three dimensional diagrams of a-X-T representing the temperature and concentration dependence of activities were successfully plotted. The calculated activities of ternary and quaternary systems at an arbitrary temperature have been statistically examined with the experimental values from the literature. Hence, this simple approach could be useful for analyzing thermodynamic properties of liquid alloy systems.

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Effect of sulfur on the hot ductility of 310S stainless steel has been studied. The hot ductility of 310S was drastically decreased with the presence of a small amount of sulfur and it was also decreased with increasing cooling rate after reheating treatment. The hot ductility was mainly governed by a reprecipitation behavior of redissolved sulfides during reheating treatment. It was found that the low melting sulfides such as Cu₂S were formed under the high cooling rate.

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The hot deformation behavior of cast SAF2507 super duplex stainless steel under hot working conditions in the temperature range of 900 to 1250℃ and strain rate range of 0.01 to 50s^(-1) has been studied using hot compression testing. The dynamic materials model has been used for developing the processing maps, which show the variation of the efficiency of power dissipation with temperature and strain rate. The processing map revealed a single domain with a peak efficiency of power dissipation of about 48% occurring at 1250℃ and 0.2s^(-1). These are the optimum conditions for hot working of SAF2507 and an elongated austenite phase divided into several equiaxed grains in microstructural observation. On the other hands, the material exhibits flow instability, manifested in the form of shear bands at strain rates higher than about 3s^(-1).

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