발간논문

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A carbon steel/Cr-cast iron bimetal produced by an alloy cored wire welding method showed a zigzag type fracture in the interface in tension tests. Results obtained from the interface were; σ_(UTS) = 29.75 (㎏/㎟) σ_(ys) =20.08 (㎏/㎟) E = 8.5 × 10＾7(psi). The evaluated value of J_(IC) was 0.7 ㎏.f/㎜. Brittle fracture were observed only in the cant structure. Wear resistance of hardfaced metal was superior to that of base metal. The wear mechanism was mostly abrasive wear. but oxidation wear and adhesive wear were also activated partly.

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The kinetics of silver cementation on lead were studied utilizing the rotation disk technique in nitrate solution. The cementation reaction was the first order with respect to silver ion concentration, and the rate determining step was found to be a mass transfer through the liquid film boundary layer. The activation energy for the cementation was calculated to be 3 ㎉/mole. An increase of the reaction rate was found as the cementation reaction progresses, and this is probably due to the turbulance of the solution and to an increase in total reacting area.

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Sintered specimens for the mechanical and corrosion tests were prepared from 316L, 410L and 434L stainless steel powder compacts with green densities in the range of 6.2∼7.0g/㎤. The experimental variables studied were green density, sintering atmosphere, temperature and time, type of lubricant used and cooling rate after sintering operation. Mechanical properties of green compacts and sintered specimens were evaluated. The corrosion tests were performed by potentiodynamic anodic polarization technique. Mechanical properties were very sensitive to the sintering atmosphere; sintering in dissociated ammonia resulted in the strengthing but embrittlement of sintered 316L, 410L and 434L stainless steel powder compacts. Their corrosion resistance was also decreased. The tensile strength was increased with increases in sintering time and temperature while the decreases in the yield strength were observed. The tensile properties of green compacts were shown to closely related to the green density. Addition of 1% acrawax as a lubricant was appeared to be most effective for the improvement of green strength.

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The hardness of TiNi alloys containing Ni from 50 at.% to 53 at.% was measured. Wear test was performed by rubbing these alloys against SUS316 or S45C. The results obtained are as follows; 1) Microvickers hardness in low load from 10gf to 100gf was very high. This is thought to be caused by the rubber elastic effect, the martensitic characteristic of these alloys. 2) The quenched Ni-Ti alloy contained Ni above 51 at.%. The hardness of these alloys in the liquid nitrogen temperature were less than in room temperature. This is thought to be due to the two reasons; one is that Ms point is below the room temperature and martensitic transformation is induced by indenter during the hardness testing, the other is the intrinsic rubber elasticity of martensite. 3) SUS316 was adhered to Ni-Ti alloy and the weight of Ni-Ti alloy was increased by 3㎎. It is thought that this is due to the high work hardenability of TiNi alloy in -196℃.

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The effect of dopants, Al₂O₃, K₂O and SiO₂ (AKS), on the microstructure of tungsten ingots and wires has been investigated. It was found that rapidly heated ingots showed finer grain size with low degree of sintering than slowly heated ingots. The AKS doped ingot showed the lowest degree of sintering whereas the KS doped ingot showed the highest. Secondary recrystallized grain structure was closely related with bubbles formed in the drawn wire. The AKS wire showed the highest bubble density whereas KS showed the lowest. As density of bubble increased, the secondary recrystallization temperature of the wire also became increased.

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Domestic titaniferrous magnetite ore contains about 20% TiO₂ and 40% Fe. To obtain pig iron and TiO₂-enriched slag suitable for the chlorinator feed to produce metal titanium, pellets made of ground ore, coke and soda ash were smelted in an arc furnace. A series of tests were conducted to determine the effects of smelting temperature and time, ratio of ore to coke, and addition of flux on the TiO₂ content in the slag. The content of TiO₂ in the most enriched slag was 52%. The iron purity in the pig iron was 94.8% and TiO₂ content in the pig iron was less than 0.003%.

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Followings were obtained through the analysis of the morphology of the planar solid-liquid interface developed in the directional solidification of Sn-2 at % Sb alloy. The marginal stability theory was also considered for the analysis. The transition of solid-liquid interface from planar to cellular was observed to be slightly faster than as expected by the theoretical criteria. It was confirmed that the increase in the growth velocity V was the dominant cause for this discrepancy rather than the decrease in the temperature gradients G_l and G_s. However, the solidification process as a whole under this condition appeared to be approximately the steady state. The different degree of the microstructural development was observed in the cross section perpendicular to the growth direction. It is believed that the variation was an intermediate stage to the final morphology of cellular interface. Two possible interpretations for this were also discussed. The critical wavelength of perturbation λ_c evaluated by applying the marginal stability theory was agreed well with the measured value of node spacing λ_n.

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Many research works for deposition of polycrystalline diamond-like carbon film are being carried out in Japan. In this report, a micro wave plasma CVD process of the diamond-like carbon film on a silicon substrate by a mixture of methane and hydrogen was described simply. The diagnostics of chemical species in the plasma was put to the test by using emission spectroscopy. The film was identified by various analytical techniques such as IR spectroscopy and Auger Electron Spectroscopy. The mechanism of such film deposition was discussed and the significance of the presence of atomic hydrogen and hydrocarbon radicals in the plasma was emphasized, There have been very few reports about the deposition of cubic or wurtzite-type boron nitride. The deposition of boron nitride film was confirmed by chemical vapor transport from solid boron particles under an Rf hydrogen-nitrogen plasma stream. The film consisted of a mixture of hexagonal and wurtzite-type boron nitride crystals was deposited on a silicon substrate. Various chemical species in the plasma were identified by a quadrupole mass spectroscopy and the mechanism of the film deposition was discussed.

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