발간논문

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The glass forming range, saturation magnetization and coercive force were studied for Co-Zr-Mo thin film alloys made by sputtering. The glass forming range was slightly expanded in the middle ratio of Zr and Mo. The relationship of magnetic moment to solute concentration could be interpreted by Friedel`s theory for Co-Zr and Co-Mo within 10 at % Mo. Dependence of saturation magnetization to total solute concentration of Co-Zr-Mo alloys was similar to that of Co-Zr alleys. Coercive force of Co-Zr-Mo alloys were studied and discussed with the concept of magneto striation. Optimum composition as soft magnetic material was considered as Co_(89.5) Zr_8 Mo_(2.5) with 12.6 kG and 8 Oe.

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Effects of cold work and aging treatment on corrosion and microhardness of duplex stainless steels were studies employing weight-loss tests, polarization tests and micronardness test. Degree of cold work applied were 15%, 30% and 40%, and temperatures for aging were 475℃, 600℃ and 800℃. Cold work enhanced the corrosion resistance, and this fact was attributed to decrease in the amount of ferrite and change in its configuration. Cold work higher than 15% was detrimental, because increase in defect concentration counteracted against the beneficial effects of ferrite. Aging treatment improved the corrosion resistance and the hardness. Spinodal decomposition at 475℃ and ferrite-austenite transformation at higher temperatures were attributed to the improvements. Applying 30% cold work followed by aging heat treatment at 475℃ was found the best in treating the duplex stainless steels studied.

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Recrystallization temperatures of original austenite and reversed austenite have been investigated in Fe-32%Ni alloy. The former was formed by diffusional transformation, and the latter by diffusionless transformation, At the same levels of deformation degree, the recrystallization temperatures were higher in the original austenite than in the reversed austenite. At the same levels of hardness, however, the recrystallization temperatures were higher in the reversed austenite than those in the original austenite. This is because the cells are smaller and the walls of the cells are thicker in the original austenite than in the reversed austenite, in addition to the difference in vacancy concentration between them, at the same levees of Hardness.

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Thin film properties generally vary by orders of magnitude depending upon preparation. In this work the crystallographie structure and the physical structure of evaporated Ti thin films resulting from various experimental conditions were investigated. The evaporated Ti thin Films were characterized by an X-ray technique for the texture, scanning electron microscopy and transmision electron microscopy for the physical structure and Auger electron spectroscopy and X-ray photoelectron spectroscopy for the chemical distribution. When the substrate temperature was below 0.3 Tm, evaporated Ti thin films were found to have very strong (00.2) preferred orientation which was independent of the substrate and the rocking curve value decreased with film thickness. The surface columnar size and the crystal grain size increased with film thickness and substrate temperature. When Ti vapour was activated, the columnar size and the grain size decreased and the columnar shape became rounded.

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A study was carried out on the microstructure and the mechanical properties of Al-Cr and Al-Cr-Zr alloy splats produced by atomization-splat-quenching method and their extruded bars. Two types of microstructure were observed on the etched cross sections of the splats: the first type was composed of microcrystallines and fine cellular dendrites (zone A) and the other contained large amount of intermetallic compounds (zone B). When Zr was added to Al-Cr alloy, the maximum solid solubility of Cr extended from 5 wt % to 8 wt % and the relative amount of zone A also increased. In comparison to Al-Cr alloy, the maximum peak hardness of the Al-Cr-Zr alloy was higher and the thermal stability was also increased. An isothermal aging of extruded bars at 350℃ of 100 hours did not affect hardness significantly.

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By modifing Johnson-Mehl-Avrami equation applicable to the isothermal phase transformation of space-random nucleation and constant growth rate, the time dependent nucleation rate could be expressed as a function of the transformation volume fraction. Using this modified J-M-A equation, we discussed the problems in evaluating the nucleation rate from In t vs ln (-ln (1 -x)) plot. Because a small chance in the shape of the In t vs ln (-ln (1-x)) plot makes extremely large variation in nucleation rate, J-M-A exponent n may lose it`s well-known meaning. One can not infer the whole nucleation procedure during phase transformation by any method using only the J-M-A equation.

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A study has been made on the effects of microstructures and textures of an extruded Al_Cu alloy (i.e., Al-4.5Cu-1.3㎎-0.1Mn). The machinability was determined by dry-cut technique and roughness of cut surfaces and chip formation were examined after solution treatment and aging of the alloy. As hardness is increased due to microstructural changes, roughness of the cut surfaces is improved. The central and surface legions of the specimen showed different machinability whose cause was analysed to be variations of textures between the two regions. Such an inhomogeniety of cutting behavior has disappeared after particles of the second phase precipitated after aging treatment

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