발간논문

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The morphology of diamond crystals grown by oxy-acetylene flame has been investigated at various radial distances in the deposition area. The main variables were deposition temperature and nozzle-to-substrate distance. It was shown that the radial variation of diamond growth shape in the deposition area was dominated by the gas species profile in the flame, rather than by the substrate temperature profile.

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The structure of AlN thin film deposited on an Al₂O₃(0001) substrate is examined using symmetric Brags diffraction and Grazing Incidence X-ray Diffraction(GID) methods. A new five-circle goniometer is adapted to carry out the GID experiments for convenience and accuracy. This goinometer consists of a conventional four-circle goniometer and a new circle segment inserted between the θ-2θ circles and the Eulerian cradle of the four-circle goniometer. It is found that the orientational relationship between AlN thin film and Al₂O₃ substrate is AlN[10 10￣]∥Al₂O₃[11 20￣] and AlN(0002)∥Al₂O₃(0006). The strain parallel to the interface is 1.0% and that perpendicular to the interface is 1.1%. The thin film is composed of small sized mosaic blocks. The size and orientational spread of the mosaic crystallites is 98Å and 2.4˚ parallel direaction to the interface, and 74Å and 2.7˚ perpendicular direction to it.

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The effects of cooling velocity, melt weight and purity of copper were reported on copper single-crystal growth by Heat Exchanger Method in this paper. Copper single-crystals could be grown at the cooling velocity lower than 1℃/min. Higher purity(99.995wt%) of copper single crystal less than 7㎝ height(radius 3.5㎝) was grown when the cooling velocity was 0.34℃/min. and the height less than 3.5㎝(radius 3.5㎝) was grown with the plane front of solid-liquid interface and of semi-ellipse, and the free surface of single crystal was solidified in the end. However in the lower purity(99.93wt%) of copper, it should be solidified with plane front at the initial stage, and cell, dendrite formed finally at the cooling velocity lower than 0.5℃/min. The significant segregation were caused when the solid-liquid interface was changed from plane front to cell structure.

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Structural characteristics as functions of Co composition and aging temperatures were investigated in the Cu-Co alloy films deposited by the thermal co-evaporation. In the low Co concentration(<25at.%), the as-deposited alloy fillms were mainly oversaturated solid solutions and in the higher concentration, they were the mixtures of oversaturated solid solutions with Co-rich particles. As the aging temperature increases, Co precipitated as fcc α-Co and the precipitation was enhanced in the higher supersaturated alloy films with the Co-rich particles. The existance of α-Co precipitates was thought to be due to the low lattice misfit strain energy and the supercooling effect. The cored structure which was composed of the low Co content outer layer and the high Co content core was developed due to diffusion of precipitated Co back into the Cu when the aging temperature increased from 500℃ to higher temperature. The measured average diameters of Co particles aged from at 400 to 650℃ for 10min. were range from about 130 to 190Å for 25at.%Co alloy film.

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Permalloy films were deposited by RF(Radio Frequency) magnetron sputtering method using several different targets which had been cold rolled and annealed at various temperatures to give different microstructures and textures. When permalloy targets are annealed at temperatures higher than 650℃, the microstructure changes from as-rolled structure to recrystallized one with fine grains, and consequently, the (110) texture structure transforms into the random texture. The residual stress of the targets decreases with the annealing temperature due to stress relaxation. The dependence of the input power on sputtering rate differs depending on the structure of targets, and the difference is increased with the Ar pressure. The deposition rate decreases with the annealing temperature when no microstructural change occurs. At the annealing temperature of about 650℃ where as-rolled structure transforms into recrystallized one, the deposition rate increases abruptly. The sudden increase in the deposition rate is related to the recrystallization of the targets. The deposition rate of thin film could be explained in terms of the changes in the stray field, residual stress, and the texture of targets accompanying the structural change.

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The differential thermal residual stress state in WC-6wt.%Ni and WC-25wt.%Ni cemented carbide composites has been studied using neutron powder diffraction. Residual strain values have been obtained from the difference in WC cell parameters in a strain-free WC powder and in the composites over the temperature range 100-900 K. The nature of stress state of WC phase in the as-produced composite was confirmed to be hydrostatic by tri-axial stress measurements. The stress state is compressive in the WC phase and tensile in the Ni binder phase as expected. The absolute stress value increases as the temperature decreased and as binder content increased. The effective stress set-up temperatures are about 1030 K for low binder composite and 990 K for high binder composite.

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The effects of dispersoid on microstructure and mechanical properties of mechanically alloyed and hot-extruded copper were investigated. Copper powders containing 1∼5% Al₂O₃ and TiB₂ as strengthening dispersoids were mechanically alloyed by milling for maximum 1000 minutes in high energy ball mill. The saturated milling time decreased with increasing dispersoid contents in MA powders. The saturated milling time of MA powders containing Al₂O₃ decreased comparing to that of MA powders containing TiB₂. In this investigation, MA copper with 5%TiB₂ content showed the superior mechanical properties at room temperature and high temperature to any other hot-extruded MA copper consolidates. This better properties of hot-extruded MA copper consolidates containing 5%TiB₂ seemed to be due to the interface precipitation of Fe-rich phase.

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The sulfidation behaviors of pure Cu, Cu Mn and Cu Ni alloys were studied in sulfur vapor atmosphere over the temperature range of 300 to 600℃. The sulfidation rates of copper were decreased significantly with increasing Mn or Ni content of the alloys, and activation energy for pure Cu was almost same with values of Cu Mn and Cu Ni alloys. Scales for the alloys always consisted of two layers, an outer layer and an inner complex layer. The outer layer always was only copper sulfides. Cu S and Cu S₄, on the other hand the inner layer which exhibited the porous structure contained two sulfides, such as nickel sulfides or manganese sulfides as well as copper sulfides. In the case of pure Cu, platinum marker was found near to the metal surface. However, for Cu Mn and Cu Ni alloys markers were found near to the interface of the inner and outer scales. From those results, the predominent defects in sulfidation and the reaction mechanisms were explained, accordingly.

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Shape memory characteristics of thermo-mechanically treated Ti-Ni-Cu alloys have been investigated by means of thermal cycling test under constant load, and then compared with those of solution treated ones. Transformation occurs in one stage, i.e., B2-B19 in the solution treated Ti-49Ni-1Cu(at%) alloy irrespective of the amount of applied stress, while in two stages, i.e., B2→R→B19` in the thermo-mechanically treated one under the applied stress less than 120 MPa, above which in one stage. i.e., B2→19`. In the Ti-46Ni-4Cu(at%) alloy, however, transformation occurs in one stage, ie., B2→B19` in both the thermo-mechanically treated and solution treated conditions. The transformation hysteresis associated with the B2↔B19` transformation increases with increasing applied stress in the solution treated alloys, while almost keeps constant in the thermo-mechanically treated alloys. The critical stress for slip deformation and the maximum recoverable transformation elongation increased largely by applying the thermo-mechanical treatment to the solution treated Ti-Ni-Cu alloys.

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In this study, the deviation of cracks from the primary slip plane in the late stage of the fatigue life is suggested to be determined by the relative orientation of Thomson`s tetrahedron with respect to the primary slip plane. By geometrical consideration of secondary slip planes with respect to primary cracks, it is suggested that a critical slip system(A6) is mast favored for secondary cracking in the presence of long Cracks. The observation of slip traces at the surface of cyclically deformed Cu-Al single crystals is consistent with the predictions from this study.

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