발간논문

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The microstructure of DC & RF sputtered MoS₂ thin films have been studied. The films have been deposited onto the stainless steel, glass and Si wafer with 4$quot; DC/RF magnetron sputtering system. The sputtered MoS₂ films showed well defined columnar-plate structure and the preferential orientation was found to be (100). The grain size increased with increase of the substrate temperature(A.T.∼350℃) and the sputtering power density(0.58W/㎠∼1.45W/㎠). AES analysis indicated that the ratio of S(152eV)/Mo(186eV) was about 8.1 which was smaller than that of the pure MoS₂(8.9). Exposure to atmosphere resulted in oxygen diffusion into MoS₂ thin films due to lack of sulfur in sputtered thin films.

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Smelting reduction technique was applied for the recovery of valuable metals such as V and Cr from LD slag using a Tamman furnace. In the present study, the parameters to increase the reduction rate and efficiency were selected by changing the slag additives, basicity, temperature and amount of reductant. The optimum basicity was found to be 1.4 and maximum reduction of V was reached to less than 0.02% V in the slag in 30 min. The temperature dependence of reduction rate calculated from the experimental data. was 0.0012∼0.0021kg/㎡·s. Metallization degree of slag was 58% (1400℃), 70%(1500℃), 74%(1550℃), 82%(1600℃) and 98%(1600℃, 30min).

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The present study is concerned with the microstructural analyses of the surface layer hardened by the irradiation of accelerated electron beam in 0.2% and 0.4%C plain carbon steels. Steel specimens were irradiated using an 1.4 MeV electron accelerator, and the microstructures of the irradiated surface regions were examined. Upon irradiation, the ferrite-pearlite matrix adjacent to the specimen surface was changed to the ferrite-martensite structure, whose interface was composed of fine particles and needle-like lamellae. In order to investigate the martensitic transformation mechanism, the simulation test including thermal cycles of abrupt heating and quenching was carried out. It was found from this test that the temperature of the irradiated surface layer was raised to about 1100℃, which was enough to obtain the surface hardening through the transformation from pearlite to martensite. It is also suggested that the proper accelerated electron beam conditions such as the carbon content and the heat input should be determined to improve microstructures for the surface hardening.

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The microstructure and magnetic properties were investigated on the crystallization of amorphous Fe_(100-x-y)B_xNb_y (5≤x≤10, 5≤x≤9) alloy ribbons, which were produced by using a single-roll melt-spinning technique. The best magnetic properties were obtained for the alloy Fe_(84)B_9Nb_7 and the magnetic properties achieved are; the effective permeability of 12,000 at 1 ㎑, do coercive force of 10 A/m and the core loss of 90 W/㎏ measured at 100 ㎑, 0.2 T. These good magnetic properties were attributed to the formation of bcc-Fe crystalline phase with about l0㎚ grain diameter. The magnetic properties were reduced abruptly as the constitution deviates from the optimum composition. The rapid deterioration of the magnetic properties are due to the formation of Fe₃B for Fe_(93-x)B_xNb_7 (B≥10 at%) alloys and Fe₂Nb for Fe_(91-x)B_9Nb_y (Nb≥8 at%) ones.

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Detailed microscopic examination and metallurgical analysis of dominant microfracture mechanisms of the 2XXX Al-SiC composites under dynamic loading are presented in this study. The materials used here were 2124 Al-7 v/o SiC_p, 2009 Al-15 v/o SiC_w and 2009 Al-15 v/o SiC_P Metallorgraphic investigations of longitudinal sections of most highly deformed areas were made to identify local Void and microcrack formation sites and to observe overall crack propagation paths. Under the quasi-static condition, microvoids initiated predominantly at whisker ends and particle edgs tend to grow along the 45-degree direction to the tensile axis by a localized mode of plastic instability. On the other hand, under dynamic condition, void initiation at whisker(particle) sides and internal whisker(particle) cracking are also observed. The dynamic crack-growth direction of then appears to deviate from the maximum shear -stress direction, so as to interconnect locally developed fracturing events in a rapid manner.

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The objectives of this study are firstly to find optimum fabrication condition of the high strength Al-Mm(misch metal)-Ni and Al-Mm-Ni-Fe amorphous alloys made by a single roll melt-spinner in air and vacuum, and secondly to investigate the correlation of the mechanical properties and microstructure of the alloys. Alloys containing about 4 at.% Mm and 10 at.% Ni content revealed uniform amorphous phase, and showed high fracture strength. Among these alloys Al_(86)-Mm₄-Ni_8-Fe₂ alloy, melt-spun in vacuum, showed the highest fracture strength of about 850MPa. Meltspun Al_(86)-Mm₄-Ni_(10) amorphous alloy showed two-stage crystallization from amorphous to amorphous matrix phase with fcc-Al particles, and then to amorphous matrix phase containing intermetallic compounds. As annealing temperature increased, fracture strength and elongation decreased in the range up to about 350℃, and then increased again. The decrease in fracture strength seems to be caused by a decrease of free volume of amorphous phase by the structural relaxation before the formation of fcc-Al particles, in conjunction with an enhancement of embrittlement after formation of fcc-Al particles. The replacement of Ni content by 2 at.% of Fe in Al_(86)-Mm₄-Ni_(10) alloy resulted in an increase of both thermal stability and the mechanical properties. This can be explained in terms of increased attractive bonding force among the constituent atoms by the replacement of Fe.

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