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Improvement of the yield ratio(YR) of a high strength structural steel has been required to enhance the resistance to seismic motion in building. Microstructural modification through thermomechanical control processing(TMCP) was attemped to lower the YR of a structural steel with 600㎫ tensile strength. In the direct quench and tempering(DQT) processing condition, finish-rolling temperature(FRT) was changed in the wide range to modify the appearence of austenite before quenching. When FRT`s were lower than 940℃ the microstructures consisted of ferrite and bainite. However, when the specimen was finish-rolled at 940℃ the microstructure was characterized as bainite phase. When the direct quench, lamellarizing and tempering(DQLT) process was applied, the mixed structure comprising continuous fine ferrite and martensite was obtained and the YR was lowered to 75%. The prior microstructure before lamellarizing heat treatment, significantly affected the YR and the final microstructures. When the bainite phase was prior microstructure, the ferrite phase acted as a continuum phase after DQLT process, and the low YR was obtained,

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Acicular γ-Fe₂O₃ particles were heated at 90℃ in alkaline solution containing Co^(+2) and Fe^(+2). The coercivity of resultant product increased from 0.2 to 0.25, Co^(+2)/Fe^(+2) molar ratio, and gradually decreased above 0.25. When cobalt content is increased, the coercivity of resultant product increased linearly. The increase of coercivity was attributed to the crystalline magnetic anisotropy of the cobalt ferrite which is conform to coating layer. The coercivity increased with the increasing seed content. The stability of temperature and the change on standing was largely influenced by the composition of coating layer and showed the most superior properties in the range of the Co^(+2)/Fe^(+2) molar ratio of 0.36∼0.5.

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The microstructural difference between thermal and stress-induced ε martensite was investigated in iron-based shape memory alloy. The thermal εmartensite plates were found to be randomly distributed with several variants, causing no shape change during cooling and heating. But stress-induced ε plates have almost single variant in one grain. Pole figure analysis showed that ε plates whose [1.63 0 1] ε direction is paralell to tensile stress are preferably formed on the deformation. The [1.63 0 1] εdirection was proved to be the most expandable one in fcc→hcp transformation by [112] γ shear deformation.

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This study was undertaken to investigate the distribution ratio of silver between metals and slags during lead slime smelting processes. The antimony activities of the lipuid Sb-Pb-Ag system at 1250K were determined by using isothermal and isopiestic equilibrium methods. At 1250K, the equilibrium distributions between the Sb₂O₃ PbO slag and Sb-Pb-Ag metal, and Sb-Pb-Bi-Ag metal were studied. The results are summarized as follows;l) The activities of Sb in liquid Sb-Pb-Ag system at 1250K showed a slight negative deviation from Raoult`s law at low Sb concentrations and obeyed Raoult`s law at high Sb concentrations. 2) Liquid Sb-Pb-Ag system presents the behaviors of regular solution in a minute error. 3) Difference between the behaviors of silver and other elements during lead slime smelting processes was also discussed based on the thermodynamic data obtained in present investigations.

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A study was undertaken to investigate the characteristic of low cycle fatigue behavior for aluminium alloy 2090 and 8090. Discontinuity of slope in the Coffin-Manson curve was observed for all the alloy systems and was attributed to difference in the deformation mode as a function of plastic strain amplitude related to fatigue crack initiation. At low applied plastic strain, strain localization by planar slip has been observed and fatigue cracks at the surface were initiated on the site of strain Localization. On the contrary, specimen cycled at high plastic strain exhibited homogeneous deformation and fatigue cracks at the surface have been observed on grain boundary. Therefore, the break in the Coffin-Manson plot is discussed in relation deformation mode with fatigue cracks initiation. Furthermore, it is observed that the decrease in elongation is due to Fe-Cu rich constituents segregated on grain boundary in Al 2090.

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Laboratory hot rolling experiments were performed to develop bake hardenable hot-rolled strips. The effects of steel chemistry as well as coiling temperature(CT) were studied to find out the optimum processing condition. It was found that the ferrite grain size was decreased as increasing the carbon content up to about 120ppm. The carbon content more than 120ppm did not affect the ferrite grain size significantly. When the carbon content was high matrix cementites were observed at the CT`s ranging between 400 and 500℃, but few matrix cementites were observed at the CT`s lower or higher than the range. Matrix cementite was not formed either when the carbon content was low. This can be analyzed by the degree of supersaturation and diffusivity of carbon. It was observed that the major factor which determined the amount of bake hardening (BH) was the content of soluble C and N. When CT was 200℃, BH was increased with the carbon content. When CT was 700℃, BH showed a maximum point at C=50-100ppm. When CT was 500℃, BH was low and did not show a carbon content dependency. This was attributed to the fact that precipitation of matrix cementites lowered the solute carbon content. BH in AI-containing steels was very low when CT was 700℃. This was thought to be due to the formation of AlN which not only decreased the solute nitrogen content but also accelerated the cementite precipitation. It was also found that fine grain size showed higher BH at a given solute (C+N) content.

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The influence of temperature and stress on the microstructural changes has been studied in Ni-base superalloy Rene 80. While some specimens were only thermally exposed, others were exposed under high temperature and stress. An external tensile stress on the specimen has been found to cause the directional coarsening of γ` precipitates which results in morphological change in γ` precipitates. In particular, the degree of morphological change in γ` precipitates was different around the carbides. This indicates that local stress around carbide varies relative to location. Rene 80 exhibited bimodal size distribution of γ` precipitates after standard heat treatment. Consequently, the variation of γ` precipitate size with exposure time was complex as compared with the systems which exhibit with unimodal size distribution. γ` precipitates have been found to obey the diffusion-controlled coarsening, and the activation energy for coarsening was about 65.1 Kcal/mole.

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The main objective of the present paper is to study on the structure and property relations of an 8090 Al-Li alloy. Particular emphasis has been placed on clarifying the origin of the anisotropy of mechanical properties which occurs along the short-transverse (S-T) direction. Although the application of stretching generally improved overall tensile properties of the 8090 plate due to the enhanced precipitation of S` phase, S-T oriented specimen in peak-aged condition showed an elongation ductility of only 1%, limiting the applicapability of the 8090 plate. For the S-T oriented specimen, examination of the fracture surfaces reveals clearly an intergranular fracture mode without any evidence of ductile fracture. Thus, fractorgaphic observation in the S-T oriented 8090 plate shows that the presence of coarse second phase particles at grain boundaries and the elongated shape of grain structure strongly influence fracture initiation process, thereby drastically reducing mechanical properties of the S-T oriented specimen.

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In order to varify the origin of the anisotropy of mechanical properties particularly in short-transverse (S-T) orientation, the micromechanism of fracture processes involved in void and microcrack formation was identified in detail using an in-situ SEM fracture technique. For the S-T oriented specimen, microcracking occurs at the coarse grain boundary particles at the relatively low stress levels. Since the crack propagation path in the S-T oriented fracture nearly coincides with the elongated grain boundary, fracture proceeds readily along the grain boundary already weakened from cracking of coarse δphases, and a very low elongation is recorded. For fracture in the L orientation, on the other hand, fracture occurs along a tortuous path mainly along the slip band because the grains are smaller and of an equiaxed form, resulting in excellent mechanical properties. In this case, the coarse phases along the grain boundary do not have a large effect on the fracture path, according to the fact that a crack propagating along the slip band leads to intergranular fracture only when it meets the grain boundary directly. Therefore, the most important factor affecting the anisotropy of mechanical properties in the 8090 Al-Li alloy plate is the grain shape because fracture mode is largely determined by the grain shape.

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The wetting phenomena between A1 matrix and metal coated SiC fiber have been studied at 670℃ for 15 min-60 min under vacuum. SiC fibers were coated about 1000Å thickness with Ag, Cu, and Ni metal in high vacuum evaporator. The wetting behavior of Al/metallic thin film/SiC fiber was analysed by SEM, AES, and XRD. The wettability of metal coated SiC fibers was better than as-recieved SiC fiber, especially Ag and Cu coated SiC fibers were more effective. It was considered Chat the driving force for wetting was increased by interfacial reaction between metallic thin film and Al melt. When interfacial reaction involved the eutectic reaction, the interfacial free energy was sufficiently reduced to improve the wetting behavior, and aluminum oxide film was easily broken down by eutectic melt. The wetting behavior of as-recieved SiC fiber was not uniform and the contact angle was larger than 90°.

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