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In order to improve the manganese yield in reduction of manganese ore in less slag blowing process at BOF, the dissolution behavior of manganese ore in slag has been studied under experimental scale. The effects of temperature, slag composition, addition of CaF₂ and pretreatment of manganese ore on the dissolution behavior into molten slag were examined. Also, the precipitation in slag during addition of manganese ore was examined by EPMA and X-ray diffraction analysis. The dissolution rate of manganese ore into molten slag increased with increasing temperature. The dissolution rate of manganese ore also increased with the increase of initial FeO, MgO, and MnO content in the first stage. The addition of CaF₂ and the pretreatment of manganese ore are very effective to promote the dissolution of manganese ore into slag.

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The effect of extrusion ratio on the mechanical perties of the SiC_p/2024 Al composites fabricated by powder extrusion has been investigated. 2024 Al powders were mixed with SiC particles(10 and 20Vol%) and then degassed at 450℃ for 60min. The SiC_p/2024 Al composites were fabricated by powder extrusion with extrusion ratios of 15:1, 25:1, 35:1 and at 500℃ at a constant ram speed of 130㎜/min. Extrusion pressure was increased with increasing the extrusion ratio. This is die to the fact that the friction force between conical die wall and extruded billet increased and also the plastic flow stress increased. It was found that the density of the composites extruded with an extrusion ratio of 35:1 was higher than that of the composites extruded with extrusion ratios of 25:1 and 15:1. Also, the composites extruded with an extrusion ratio of 35:1 showed the highest tensile strength and elongation. This is attributable to a decrease in the porosity of the matrix and matrix/reinforcement interface and the homogeneous distribution of SiC particle in the matrix caused by an enhanced plastic flow of the 2024 Al matrix powders.

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One of the major issues in fabricating the Al alloy composites reinforced with SiC particulates is to avoid interfacial reaction products, i.e., Al₄C₃ and Si. The formation of such interfacial reaction products can be supressed by the presence of adequate amount of Si within the matrix of the composite. Equilibrium Si contents required to prevent the interfacial reaction in various SiCp/wrought Al composite were predicted both using theoretical calculations and experimental method. According to the results, equilibrium Si contents increased with increasing temperature ; When the composite is exposed at temperatures below the solidus of the matrix, less than 1 at.% of Si was found out to be enough for preventing the interfacial reaction. However, Si contents required to prevent the interfacial reaction was observed to increase substantially at temperatures near 600℃ such that more: than 5 at% of Si was required to prohibit the interfacial reaction even at 620℃. Application of such results for designing the matrix alloy and selecting process parameters for the semi-solid forming was demonstrated.

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Functionally graded thermal barrier coating(TBC) consisting of NiCrAlY and 8wt% Y₂O₃,-ZrO₂(YSZ) was produced on a Co-base superalloy (HAYNESS 188) substrate using the Ar shielded air plasma spraying method. Functional grading was obtained by the stepwise change of metal/ceramic composition. 1, 2 and 4 layers with different compsotional combinations were inserted between metal and ceramic layers. Microstructure of the functionally graded thermal barrier coating was examined to check proper grading of metal/ceramic compositions and features of defects. No particular defect which may affect the properties of TBS significantly was found at interface and through thickness of the graded layers even though some unavoidable oxides and pores were observed. Microstructural observation revealed successfully fabrication of functionally graded TBC by plasma spraying technique. A dhesion strength of TBC with 4 layers was measured with the highest value. In other words, the strength incerased with more smooth change of metal/ceramic composition within TBC. It assures the evidence that functional grading tend; to improve the strength removing the sharp interface and relieving the internal stress level due to the thermal mismach between metal and cermic.

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Titanium nitride(TiN) films were deposited on M2 high speed steel(HSS) by the thermally activated chemical vapor deposition using TiCl₄, NH₃, and H₂ as reactive gases at temperature range between 600 and 900℃. With increase of the deposition temperature the column site in TiN film increased, while the chlorine content decreased. The adhesion strength of the TiN films to the substrate also increased with the deposition temperature. NH₃, pretreatment at the deposition temperature was studied to enhance the adhesion of the TiN films deposited at 600℃. It has been found out that the adhesion property has been improved when the NH₃ pretreatment had been carried out at the NH, pressure of more than 5.0torr.

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The effect of microstructure on the electromigration failure was studied in Al-2wt.%Cu conducting lines patterned from 4800Å-thick and l㎛ wide sputtered films. The grain structures of the lines are controlled by varying post-pattern annealing temperature and time to promote bamboo structures. The lines are subjected to a current density of 2.0×l0^6 A/㎠ at 225℃. Substantial lifetime improvement in post-pattern annealed samples is attributed to grain growth that induces near-bamboo structures. Failure kinetics is studied as a function of annealing time or temperature; the results suggest that, to improve the reliability, increasing annealing temperature is more effective than increasing annealing time.

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Hot rolling process using the pack rolling method was studied to obtain an optimal microstructure in TiAl base alloys, Stainless steel was used for canning. Rolling was conducted when the can surface temperature reached until 800℃ from the soaking at 1050℃. The average strain rate was 3x10^(-1)s^(-1) and a reduction per one pass was amounted to 10% with respect to remaining sample thickness. Rolling process was controlled to make the flow stress condition of the sample and canning material same. As a result, successful pack rolling to 80% reduction of the sample without cracking was accomplished. However, this success depends upon the starting microstructure. The alloy with duplex (gamma+lamellar) microstructure was rolled up to 80%o reduction, while the one with nearly lamellar microstructure was failed to roll successfully. It can be argued that lamellar grains oriented to a hard mode deformation yield locally higher flow stress than the other part of the sample. This leads to the difference in flow stress between can and sample, although the samples are not the PST single crystals. A difference in flow stress between can and sample is believed to yield a tensile residual stress condition on the sample surface and eventually Lead to cracking.

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The effect of Al concentration and third element addition on the directionally solidified (DS) TiAl alloys were systematically investigated in order to get a basic conception for control of lamellar boundary orientation. DS ingots have been grown by the arc melted unidirectional solidification equipment without seed materials. Some β stabilizing elements such as Mo, Nb and Cr have been added in order to increase phase field in the binary system. In the case of Ti-46Al-2Mo, Ti-96Al-2Mb and Ti-46Al-2Cr DS ingot grown at a growth rate of 90㎜ hr, it has been found that the lamellar orientation was aligned nearly 0˚ to 45˚ to the growth direction. Therefore, it could be suggested that there has been great possibility to align lamellar orientation by adding β stabilizing elements such as Mo, Nb and Cr. In the case of Ti-47.5Al-2.5Mo DS ingot grown at a growth rate of 180㎜/hr and 360㎜/hr, the lamellar boundary was nearly perpendicular to the growth direction. However, when the directional solidification was performed at a growth rate of 90㎜/hr, the lamellar boundary orientation of Ti-47.5Al-2.5Mo DS ingot was nearly parallel to the growth direction. These results indicate that lamellar boundary orientation of DS ingot may been affected by the growth rate as well as composition.

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New zirconium alloys of Zr-0.8Sn-xNb(x=0.2, 0.4, 0.8, 1.2) were manufactured into sheet by the qualified procedure; arc melting, beta-quenching, hot rolling, cold rolling, and annealing. Corrosion and mechanical properties with variation of Nb-content were investigated to find the optimal niobium content for new Zr alloy. Corrosion test was carried out in autoclave under 420℃ steam. Corrosion rate and hydrogen pickup decreased with increasing the Nb-content. The observation of oxide structure by using low angle diffraction method of X-ray showed that the amount of tetra-ZrO₂ in oxide increased with increasing the Nb-content. It is considered that Nb has an effect retarding the transition of oxide from tetra-ZrO₂ to mono-ZrO₂ which is porous and nonprotective oxide. Mechanical strength increased for the high Nb-containing alloy showing the solution hardening of Nb. Two type of precipitate. Zr-Nb-Fe and β-Zr, were found in Zr-0.8Sn-xNb alloys and corrosion resistance improved in the precipitate size above 0.1 ㎛.

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Effects of solidification rate and quenching temperature on the microstructures were investigated in hypereutectic Al-Si alloy. In the phosphorus-treated alloy the primary silicon size reduced with increasing solidification rate in the range of 0.6-10℃/sec, while in the non-treated alloy it was not sensitive to the solidification rate in the same range. There exhibited a transition point of primary silicon size with quenching temperature during the solidification of hypereutectic Al-Si alloy.

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