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The precipitation behaviors including the precipitation sequence, the varieties of precipitates, and interrelation between δ` and third precipitates in Al-2.35%Li-1.45%Cu alloy were investigated by employing adiabatic calorimeter, transmission electron microscopy and hardness tester. The results obtained were as follows. The precipitation sequence was as follows : Supersaturated solid solution →(δ` + T₁,)→T₁. The endothermic reactions corresponding to δ` or T₁ phase were appeared on the S-T curves obtained from as-quenched specimens, the difference in specific heat between exothermic and endothermic concerned with the formation and dissolution of δ` was 42J/mole, which was caused by the precipitation of δ` phase formed during quenching. Another mechanisms to form platelike. δ precipitates by T₁/δ` interrelations were found. In the peak hardness conditions aged at 190℃ for 24 hours, the high densities δ` and T₁ phases coexisted, and the average diameter of δ` phases were 160Å.

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Improvements of magnetic properties of Fe-Cr-Co permanent magnets by Ti and Cu addition and deformation aging were investigated. Sheet magnets of the Fe-CrCo base alloys were produced through the deformation aging processes consisting of primany aging for spinodal decomposition, intermediate cold rolling, and final aging. The microstrucures of the alloys were studied by TEM and the magnetic properties were measured by VSM. The addition of Ti increased B, and (BH)_(max) by suppressing the precipitation of a nonmagnetic second phase during the final aging. iHc was also increased by Cu addition. The addition of both Ti and Cu resulted in the highest enhancement of the magnetic properties after continuous cooling at 40℃/h rate and isothermal holding at 610℃ for 2 hours.

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The effects of annealing on the magnetic properties were investigated for Co_(70)Mn_6Cr₄B_(16)Si₄ soft magnetic amorphous alloys which have high saturation mangetization, low coercive force and high permeability as well as possibility of nonmagnetic field annealing. In this study, amorphous alloys were annealed at Ar atmosphere tube furnace with various annealing methods. Coercive force and maximum permeability of these alloys were measured by DC and AC recording fluxmeter. Magnetic domain patterns of these alloys were observed by Bitter method. Magnetic properties were improved somewhat by nonmagnetic field annealing owing to structure and stress relaxation. Magnetic properties were remarkably improved by magnetic field annealing. This seems due to disappearance of maze domains and formation of new domains. For the overall improvement of the magnetic properties, existence of stable amorphous structure and longitudinal magnetic field annealing were preffered at DC and low frequency ranges, while microcrystalline modulation and transverse magentic field annealing at high frequencies

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A relationship has been establish between the prior austenite grain size and the bainite transformation start temperature (BTST) during air cooling for low carbon Mn1/2Mo-B steels. It has been found from the experiment that the BTST usually increase with austenitizing temperature. An abrupt increase in the BTST was observed when particularly austenitized in the austenitizing temperature range of between 975℃ and 1000 ℃. The temperature dependence of the BTST appeared to be the same as the grain growth behavior of prior austenite. It has therefore been shown that the BTST has a close relationship with the grain growth characteristics of prior austenite and that it is lowered in steels with fine grain sizes during austenitization, being further lowered by the addition of Mn. Consequently, this study has been performed to qualitatively discuss some reasonable explanations for these phenomena.

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Ammonium thiosulphate was chosen as lixiviant and various tests were performed to find optimum leaching conditions in extraction of gold from a gold ore. Parameters investigated were pH, temperature, amount of lixiviant, pulp density and stirring rate. Catalytic effect of cupric ion was evaluated. Apparent activation energy of the leaching reaction was found to be 58.4 kJ/㏖ and the rate was controlled by the chemical reaction

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The effects of strain on structure and transformation characteristics of Cu-21wt%Zn-6wt%Al polycrystalline alloys have been studied. The alloys were subjected to tensile and cold rolled deformation. In tensile test, elongation was about 5%. The mechanism of strain recovery of parent phase was pseudoelastic effects by strain induced martensite formation, and that of martensite phase was shape memory effects by coalescence and rearrangement of martensite plate variants. The amount of strain recovery was reduced as increase of deformation. Martensite-to-martensite transformations of cold rolled specimens had been studied by X-ray diffraction and transmission electron microscope. In this alloy composition, 18R martensite structure was transformed to 6R structure by deformation. Parent phase, which had DO₃ structure, was transformed to 18R martensite structure, then it was transformed to 6R structure by further deformation. The procedure of phase change was same as low Al composition alloys. The amount of deformation that 6R structure was stable and peaks were detected by X-ray was about 40% of cold rolling

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The effect of Al addition on the interlamellar spacing of pearlite in ultra high carbon steels (UHCS) has been investigated. 0.32∼1.75wt%Al were added to 1.2%C-1.5% Cr-UHCS. Isothermal pearlitic transformation experiments were performed at undercoolings of 50℃, 100℃ and 130℃ below the eutectoid transformation temperature. When transformed at undercoolings of 100℃ and 130℃, the interlamellar spacing of pearlite decreased with Al contents. This fact resulted from the decrease of interfacial energy due to the reduction of lattice mismatch between ferrite and cementite by Al partitioning. However, at the undercoolling of 50℃, the interlamellar spacing was independent of Al contents due to dominant Cr partitioning.

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Hot upsetting experiments were carried out in the temperature range 700-950℃ on steel powder preforms presintered at 700℃. The influence of hot upsetting temperature on the stress connected with phase transformation and restoration mechanism was specially studied by investigating hot deformation behavior and microstructure analysis. Following conclusions were drawn on the basis of the present study. -A deep minimum and maximum in stress were found in the temperature range 800-900℃ for almost all powder preforms. -The flow stress during hot upsetting was directly related to α-γ phase transformation. -The flow stress during hot upsetting was dependent on the amounts of high-strength austenite and low-strength ferrite for carbon added powder preforms. -Major restoration mechanism during hat deformation in the ferrite range is dynamic recovery.

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Precipitation strengthening mechanisms using tensile test and transmission electron microscopy (TEM) were investigated in two alloys of Al-2.33Li-2.48Cu(-0.09Zr) and Al-2.39Li-1.50Cu(-0.09Zr). In both cases, primary strengthening originates from two different types of precipitates of δ` and T₁ phases. Retrogression technique has been employed in order to estimate the contribution of each types of precipitates. The strength of the alloys increased by applying a small amount of tensile stretch after the solution treatment prior to aging. This was shown to be primarily due to the enhancement of the nucleation rate of the T₁ phase. Results suggest that the chemical strengthening is the principle strengthening mechanism of the T, precipitates. Calculated interfacial energy of the edge of the T₁ phase was 2.82 J/㎡. Strengthening by δ` precipitates was best explained by the mechanism of the order strengthening in which the trailing dislocations pull off immediately from the encountering particles. The addition rule of the contributions from these distinctively different obstacles has been tested and was found to be best satisfied with the addition exponent, q=1. 4.

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As a first step to obtain a high purity vanadium, the purification procedure of commercial grade vanadium pentaoxide has been studied. The V₂O_5 has been converted to V(OH)₂F₃ by fusing with NH₄F· HF at 160℃ To eliminate insoluble impurites, the product has been leached out with hot water. The precipitation of NH₄VO₃ from filtered leaching solution is carried out by adjusting pH with NH₄OH. Redissolving the precipitate and stabilizing Si as a complex by adding NH₄F·HF are found to be effective to reduce the Si content. However, the rate of second precipitation is extremely slow. To improve the rate, the effect of seed and alcohol has been investigated. The addition of C₂H_5OH as a catalyst not only accelerates the rate of ppt but improves recovery up to 98%. All the products have been examined by microscope, X-ray diffraction and ICP to clarify the structure and contents of impurities.

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