발간논문

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Forming limit diagram for an electrogalvanized steel sheet has been measured by hemispherical punch stretching. The experimental forming limit diagram has been compared with results calculated using the shear instability criterion and the M-K model which takes into account a strain gradient effect resulting from bending (curvature) of a flat sheet by punch stretching. The calculated results are in good agreement with experimental data.

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Improved Zr alloys for nuclear fuel cladding were designed by changing of the chemical compositions of Zircaloy-4. Both Sn and oxygen contents were varied from 0wt.% to 1wt.% and 0.1wt.% to 0.8wt.%, repectively, in order to find the optimum oxygen content to compensate the loss of strength when the Sn content reduced for improving corrosion property. As oxygen content increased from 0.1wt.% to 0.2wt.%, 0.5wt.%, 0.8wt.%, the Ultimate Tensile Strength(UTS) of specimens containing 0wt.% Sn increased by 31%, 98%, 116%. These increases appeared to be due to the effect of solid solution strengthening of oxygen. Specimens containing 0.5wt.% Sn and 1wt.% Sn showed the similar results. When Sn content decreased from 1wt.% to 0wt.%, UTS decreased by 17%. Therefore, it was concluded that the addition of 0.2wt.% oxygen could adequately make up the decrease in UTS when Sn content decreased from 1wt.% to 0wt.%.

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The p-type thermoelectrics of (Sb₂Te₃)_(0.70)(Bi₂Te₃)_(0.25)(Sb₂Se₃)_(0.05) doped with various amounts of Te were prepared by pressure-assisted resistance/spark sintering technique. Property variations of the materials were investigated as a function of variables, such as powder size and amount of the dopant. The sintering process caused anisotropy in electrical and thermal conductivities as well as in microstructure of the materials. Enhanced values of figure of merit(F.O.M) were obtained thanks to the anisotropy; ie, the material doped with 3- and 4-wt% of Te showed F. O. M, of 2.2×10^(-3)K^(-1) and 2.0×10^(-3)K^(-1) at room temperature, respectively. These values are about 70% of that reported for unidirectionally grown crystal.

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The roles of Sn addition and hot band annealing on the magnetic properties of the nonoriented electrical steel containing 1.4wt% of Si were investigated in the range of 880℃-1100℃ of the final annealing temperature. It has been found that the addition of Sn modifies the texture obtained after the final annealing more favorable to magnetic properties. Both the core loss and magnetic induction of Sn added specimen showed continuing improvement with the increase of the final annealing temperature, whereas those of Sn free specimen deteriorated beyond a certain temperature. The hot band annealing also resulted in the improvement of magnetic properties due to the better texture formation, however its effect was found to be less than that of Sn addition, especially at higher temperature.

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Thermal sprayed porous Al₂O₃ coatings on steel have given good protection against abrasion, but poor corrosion protection. Therefore, porosity of thermal sprayed porous Al₂O₃ coatings sealed by several techniques for improvement of corrosion protection and chemical properties of sealed Al₂O₃ coatings were examined for surface modification in this study. As a result, we have investigated that porous control in thermal sprayed porous Al₂O₃ coatings was good by molten Cu dipping process. Wear and corrosion resistance of sealed Al₂O₃ coatings sealed by molten Cu were excellent.

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The purpose of this paper is to introduce the parameter A(t) which can characterize the local creep strain distribution by using a computer aided fine grid method. The local creep strain distribution in a region of 150㎛×150㎛ surrounding a crack tip of 2024-T6Al alloy was investigated at 453K, 473K, 493K and 523K using compact tension(CT) specimens. The dependence of loading levels, temperatures and time for the local creep strain distributions were also investigated. So, the magnitude of the local creep strain distribution could be characterized by the parameter A(t), which was proposed by the present author, in the following equation; ε_(y, c)(r,θ,t)=A(t)·g(r)·f(θ) where f(θ)=cos(θ/2)·(1+2/3sin²(3θ/2)) g(r)=r^(-1)

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