발간논문

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continuous and interrupted torsion tests have been conducted in the temperature range of 320-520℃ at constant strain rates of 1.26-5.71×10^-3 sec^-1 on an Al-Cu-Mg alloy. During the continuous deformation, dynamic recrystallization was observed above 370℃ and the nuclcation of the recrystallization at dislocation clusters or adjacent to second phase particle. The presence of deformation substructure in the recrystallized grain provided a direct evidence that recrystallization had occurred during the deformation. In the interrupted tests, duration of the interruptions were 10, 20, or 40 sec at egual strain intervals of either 0.4 or 0.6. During the interrupted deformation, the major softening mechanism was static recovery and partially static recrystallization above 370℃. The degree of softening was augmented by increase in the temperature, the interruption strain, and the interruption time.

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Microstructures of rapidly quenched Al-Co alloys made by a melt spinner were investigated and in-situ decomposition behavior of the solidified microstructures were also studied. Two regions of microstructures were observed in the as-quenched strips; one was a chilled structure formed on the side facing the copper substrate and the other was a free surface structure on the opposite side The chill structure consisted of micrograins and fine precipitates, i.e. B phase, which are metastable and have (001)_(At),//[001]_B and (130)_(At)//[110]_B orientation relationship with Al matrix. The free surface structure was composed of large and stable Al_9Co₂ precipitates surrounded by microdendritic, eutectic and cell structures. Upon annealing it was found that the finer the micro-structure, the faster the decomposition accompanied by nucleation of the slowly growing precipitates. The microhardness of the as-quenched structure increased with increasing Co contents and with addition of the third elements, and the value decreased monotonically with aging time and temperature. Among the various third elements tried, Mn showed the most effective results in hardness increase.

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Creep behaviors of solution treated, solution and precipitation heat treated, and solution, precipitation and carburization treated Nimonic 86 alloys were compared. Solution treatments were carried out at 1150℃ for 2 hours and precipitation treatments were performed at 900℃ for 200 and 1000 hours. Carburization treatments were performed during precipitation treatment using carburizing atmosphere. Creep tests were carried out up to 1200 hours at 850 and 950℃. Precipitation heat treatment decreased the creep resistance compared to the solution treatment. and the carburization treatment significantly increased the creep resistance, especially at 950℃. The results were explained by the relative amounts, size, and distribution of carbide precipftates.

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Experiments were carried out to study the adsorption of silver from a cyanide solution on activated carbon. The tests were conducted on a variation of inital silver concentration (Co), carbon amount(W). mixing speed, particle size and adsorption temperature. The experimental data were found to fit Freundlich adsorption isotherm as well as Langmuir adsorption isotherm. It was found that the loading carpacity of the carbon was 20 ㎎ Ag/g carbon. The isosteric heat of adsorption was found to be 1.48 ㎉/g-mole, indicating physical adsorption. The experimental results were finally compared with the theoretical results obtained by the mathematical modeling equation. A correlation equation was also developed to predict the late of apparent adsorption. Good agreements were obtained.

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Precipitation behavior of carbides and texture change in a deep drawing sheet steel were studied by heat treating in a production scale continuous annealing line. Effect of annealing, quenching and overaging temperatures were investigated. The site of carbides precipitated during overaging treatments became larger and the Vickers hardness number decreased as the temperatures for quenching and overaging increased. After a overaging treatment at 350℃, finely dispersed plate-like carbides were precipitated in the matrix, white at overaging treatments of 400℃, carbides precipitated along grain boundaries in a form of film and within matrix in a form of coarse particles. The recrystallized structure showed a (111) type texture with the main component of (111) [1￣1￣2]. The(111) pole intensity and I_(222) I_(200) became higher as the annealing temperature increased within the α-phase region.

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The formation of solid solution compounds and age hardening phenomena in rapidly solidified Al-Zr-V alloys were studied. Variations in microstructure and microhardness during isochronal and isothermal aging heat treatment were investigated. rho composition of Al₃(Zr, V) compounds was studied by electron prove microanalyzer. The lattice parameter of metastable cubic Al₃Zr phase can be changed, so does the lattice mismatch between Al-matrix and Al₃(Zr, V), by solid solution of V in Al₃Zr phase. The control of the lattice constants of Al₃(Zr, V) phase was resulted in the improved peak hardness and thermal stability of rapidly solidified Al-Zr-V alloys.

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